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Hypophosphatasia (HPP) is a congenital skeletal disease. Impairment of bone mineralization and seizures are due to a deficiency of tissue-nonspecific alkaline phosphatase (TNAP). Enzyme replacement therapy (ERT) is available as a highly successful treatment for pediatric-onset HPP. However, the potential for prenatal ERT has not been fully investigated to date. In this study, we assessed outcomes and maternal safety using a combinational approach with prenatal and postnatal administration of recombinant TNAP in Akp2−/− mice as a model of infantile HPP. For the prenatal ERT, we administered subcutaneous injections of recombinant TNAP to pregnant mice from embryonic day 11.5–14.5 until delivery, and then sequentially to Akp2−/− pups from birth to day 18. For the postnatal ERT, we injected Akp2−/− pups from birth until day 18. Prenatal ERT did not cause any ectopic mineralization in heterozygous maternal mice. Both prenatal and postnatal ERT preserved growth, survival rate and improved bone calcification in Akp2−/− mice. However, the effects of additional prenatal treatment to newborn mice appeared to be minimal, and the difference between prenatal and postnatal ERT was subtle. Further improvement of the prenatal ERT schedule and long-term observation will be required. The present paper sets a standard for such future studies.

Hypophosphatasia (HPP) ORPHA 436 is a rare disease with an autosomal recessive/autosomal dominant mode of inheritance due to mutations in the ALPL gene mapped on chromosome 1p36.12, encoding a nonspecific tissue isoenzyme alkaline phosphate (TNSALP). Currently, there are more than 400 known mutations in the ALPL gene. HPF is characterized by variability of manifestations from a mild course with minor damage to bones and teeth to severe forms with damage to the nervous system, lungs, and kidneys. In different countries, data on the prevalence of HPP differ, the average prevalence of severe forms is ~ 3.3 cases per 1 million newborns. In Europe, the prevalence of severe forms is 1: 300000 and moderately severe 1: 63701. The prevalence of mild HPP is thought to be much higher. The expected prevalence of severe forms in the Russian Federation is 1: 100000. GPP is diagnosed in patients of any age (with manifestation in utero, in childhood, or in adulthood).HPP is an orphan disease, occurring in patients with damage to many organs and systems: bone (osteoporosis, rickets, fractures, growth retardation), lungs (hypoplasia of the lungs, respiratory failure), central nervous system (vitamin B-dependent convulsions), kidney (calciuria, nephrocalcinosis, chronic kidney disease). In the absence of timely enzyme replacement therapy for severe forms of HPP, characterized by a progressive course, the prognosis for life is unfavorable. The only effective treatment for patients is enzyme replacement therapy in combination with symptomatic therapy. The article presents the features of the phenotype and genotype, clinical forms of HPP (perinatal severe, lethal, perinatal benign, infant, pediatric, adult, and odontohypophosphatasia), methods of early diagnosis, the strategy of pathogenetic enzyme replacement therapy of severe and moderate forms in pediatric and adult patients. In the absence of a timely diagnosis, pathogenetic treatment of GFF, there is a high risk of progression with disability and death.

Objectives With the advent of asfotase alfa, the enzyme replacement therapy (ERT) approved for hypophosphatasia (HPP), health care providers need to navigate management of ERT during critical illness. Case presentation We present the case of a young girl, treated with ERT for severe perinatal HPP, who had cardiorespiratory arrest in the setting of influenza A. Her life-saving treatment involving extra corporeal membrane oxygenation (ECMO) required a two-week interruption of ERT leading to persistent hypercalcemia and hyperphosphatemia. A three year old female presented with respiratory distress and blood tinged secretions. She was influenza A positive with bilateral opacities on chest X-ray (CXR). Worsening respiratory distress and bradycardic arrest required intubation, CPR and venoarterial ECMO cannulation. She remained on ECMO for 10 days with anticoagulation restrictions requiring her thrice-weekly subcutaneous ERT to be held. Hypercalcemia (12.3 mg/dL) and hyperphosphatemia (7.6 mg/dL) developed two weeks after restarting ERT and resolved six weeks later. Conclusions We highlight that the obligatory cessation of ERT while on ECMO led to the loss of functional TNSALP with a profound decrease in bone mineralization leading to excess circulating calcium and phosphorus. In cases where it is necessary to interrupt ERT, we advise close monitoring of calcium and phosphorous levels.

Hypophosphatasia is a rare metabolic inherited dento-osseous disorder. Although there is some available literature on various dental characteristics of hypophosphatasia patients, few reports focus on the effects of hypophosphatasia on the permanent dentition and prosthodontic rehabilitation, particularly in relation to the use of dental implants. This paper reports a case with hypophosphatasia and prosthodontic rehabilitation using dental implants with 7-year follow-up.

Hypophosphatasia (HPP) is an inherited skeletal disease characterized by defective bone and tooth mineralization due to a deficiency in tissue-nonspecific alkaline phosphatase (TNALP). Patients with the severe infantile form of HPP may appear normal at birth, but their prognosis is very poor. To develop a practical gene therapy for HPP, we endeavored to phenotypically correct TNALP knockout (Akp2−/−) mice through adeno-associated virus type 8 (AAV8) vector-mediated, muscle-directed, TNALP expression. Following treatment of neonatal Akp2−/− mice with a single intramuscular injection of ARU-2801 (AAV8-TNALP-D10-vector) at 1.0 × 1012 vector genomes/body, high plasma ALP levels (19.38 ± 5.02 U/mL) were detected for up to 18 months, and computed tomography analysis showed mature bone mineralization. Histochemical staining for ALP activity in the knee joint revealed ALP activity on the surface of the endosteal bone of mice. Throughout their lives, the surviving treated Akp2−/− mice exhibited normal physical activity and a healthy appearance, whereas untreated controls died within 3 weeks. No ectopic calcification or abnormal calcium metabolism was detected in the treated mice. These findings suggest that ARU-2801-mediated neonatal intramuscular gene therapy is both safe and effective, and that this strategy could be a practical option for treatment of the severe infantile form of HPP., Graphical abstract, We succeeded in treating hypophosphatasia (HPP) model mice by a single intramuscular injection of adeno-associated virus type 8 (AAV8) vector expressing tissue-nonspecific alkaline phosphatase (TNALP) without any adverse effects. This AAV8 vector-related enzyme replacement therapy is a practical and useful approach to treating HPP patients.

Summary There is limited understanding of how asfotase alfa affects mineral metabolism and bone turnover in adults with pediatric-onset hypophosphatasia. This study showed that adults with hypophosphatasia treated with asfotase alfa experienced significant changes in biochemical markers of bone and mineral metabolism, possibly reflecting enhanced bone remodeling of previously osteomalacic bone. Introduction Hypophosphatasia (HPP), due to a tissue nonspecific alkaline phosphatase (TNSALP) deficiency, can cause impaired bone mineralization and turnover. Although HPP may be treated with asfotase alfa, an enzyme replacement therapy, limited data are available on how treatment with asfotase alfa affects mineral metabolism and bone turnover in adults with HPP. Methods ALP substrates, bone turnover and mineral metabolism markers, and bone mineral density (BMD) data from EmPATHY, a single-center, observational study of adults (≥ 18 years) with pediatric-onset HPP treated with asfotase alfa (NCT03418389), were collected during routine clinical care and analyzed from baseline through 24 months of treatment. Results Data from 21 patients showed significantly increased ALP activity and reduced urine phosphoethanolamine (PEA)/creatinine (Cr) ratios after baseline through 24 months of asfotase alfa treatment. There were significant transient increases in parathyroid hormone 1-84 (PTH), osteocalcin, and procollagen type 1 N-propeptide (P1NP) levels at 3 and 6 months and in tartrate-resistant acid phosphatase 5b (TRAP5b) levels at 3 months, with a significant decrease in N-terminal telopeptide of type 1 collagen (NTX) levels at 24 months. Lumbar spine BMD T scores continuously increased during treatment. Conclusion Significant changes in bone turnover and mineral metabolism markers after asfotase alfa treatment suggest that treatment-mediated mineralization may enable remodeling and bone turnover on previously unmineralized surfaces. Urine PEA/Cr ratios may be a useful parameter in monitoring treatment during routine care. Supplementary Information The online version contains supplementary material available at 10.1007/s00198-021-06025-y.

Hypophosphatasia is a rare metabolic disease resulting from variant(s) in the gene encoding tissue-nonspecific isozyme of alkaline phosphatase. In this 13-week, Phase 2a, multicenter, randomized, open-label, dose-response study (ClinicalTrials.gov: NCT02797821), the pharmacokinetics of asfotase alfa, an enzyme replacement therapy approved for the treatment of hypophosphatasia, was assessed in adult patients with pediatric-onset hypophosphatasia. In total, 27 adults were randomized 1:1:1 to a single subcutaneous dose of asfotase alfa (0.5, 2.0, or 3.0 mg/kg) during Week 1. From Weeks 3 to 9, patients received 0.5, 2.0, or 3.0 mg/kg subcutaneously 3 times per week (equivalent to 1.5, 6.0, or 9.0 mg/kg/wk, respectively). Noncompartmental analysis revealed exposure (maximum concentration in the dosing interval and area under the concentration-time curve from time zero to infinity) to asfotase alfa increased between single- and multiple-dose administration and with increasing doses; however, extensive interindividual variability was observed in the concentration-versus-time profiles within each dose cohort. Median terminal elimination half-life was ∼5 days following multiple-dose administration, with steady state achieved by ∼Day 29. Dose-normalized exposure data indicated that asfotase alfa activity was approximately dose-proportional within the studied dose range. Additionally, dose-normalized exposure was comparable across body mass index categories of

Hypophosphatasia (HPP) is caused by loss‐of‐function mutations in the ALPL gene that encodes tissue‐nonspecific alkaline phosphatase (TNAP), whose deficiency results in the accumulation of extracellular inorganic pyrophosphate (PPi), a potent mineralization inhibitor. Skeletal and dental hypomineralization characterizes HPP, with disease severity varying from life‐threatening perinatal or infantile forms to milder forms that manifest in adulthood or only affect the dentition. Enzyme replacement therapy (ERT) using mineral‐targeted recombinant TNAP (Strensiq/asfotase alfa) markedly improves the life span, skeletal phenotype, motor function, and quality of life of patients with HPP, though limitations of ERT include frequent injections due to a short elimination half‐life of 2.28 days and injection site reactions. We tested the efficacy of a single intramuscular administration of adeno‐associated virus 8 (AAV8) encoding TNAP‐D10 to increase the life span and improve the skeletal and dentoalveolar phenotypes in TNAP knockout (Alpl −/−) mice, a murine model for severe infantile HPP. Alpl −/− mice received 3 × 1011 vector genomes/body of AAV8‐TNAP‐D10 within 5 days postnatal (dpn). AAV8‐TNAP‐D10 elevated serum ALP activity and suppressed plasma PPi. Treatment extended life span of Alpl −/− mice, and no ectopic calcifications were observed in the kidneys, aorta, coronary arteries, or brain in the 70 dpn observational window. Treated Alpl −/− mice did not show signs of rickets, including bowing of long bones, enlargement of epiphyses, or fractures. Bone microstructure of treated Alpl −/− mice was similar to wild type, with a few persistent small cortical and trabecular defects. Histology showed no measurable osteoid accumulation but reduced bone volume fraction in treated Alpl −/− mice versus controls. Treated Alpl −/− mice featured normal molar and incisor dentoalveolar tissues, with the exceptions of slightly reduced molar enamel and alveolar bone density. Histology showed the presence of cementum and normal periodontal ligament attachment. These results support gene therapy as a promising alternative to ERT for the treatment of HPP. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Hypophosphatasia (HPT) and cleidocranial dysplasia (CCD) are rare genetic disorders characterized by both defective ossification and bone mineralization. Patients usually present with craniosynostosis and cranial defects which in many cases require surgical repair. There is only 1 reported case of combined HPT and CCD in the literature. Our reported case involves a 3.5-year-old girl with concomitant homozygous CCD and heterozygous HPT. The child had an extended cranial defect since birth which improved with the administration of Strensiq and was followed until preschool age. Bone defects were relatively minor on revaluation. Due to the limited final defect, we decided not to intervene. In HPT-CCD patients, bone defects are overestimated due to osteomalacia, and thus, management strategy should be less aggressive. They should undergo surgical repair with cranioplasty with the use of cement and/or titanium meshes in case of extended final defects.

The article presents a clinical case report of hypophosphatasia, a rare congenital genetically determined disease diagnosed in a boy at the age of 3 years and 6 months. The diagnostic search took more than 2 years before the correct diagnosis was made, which is explained by the rarity of the disease and the lack of doctors awareness about it. The pathology was suspected on the basis of a combination of clinical evidence and characteristic complaints (early loss of primary teeth with an unchanged root, rickets-like skeletal deformities, motility disorders) in combination with a pathologically low level of alkaline phosphatase. The detection of mutations characteristic of the disease in the ALPL gene in the boy, his mother and father made it possible to finally confirm the diagnosis. The patient received a 7-month course of enzyme replacement therapy with Asfotase alfa, which significantly slowed down the progression of the disease and was not accompanied by the development of side effects. A feature of the patient's disease is the involvement of the urinary system in the pathological process, which is manifested by hypercalciuria, nephrocalcinosis and decreased renal function.

Background Hypophosphatasia (HPP), a rare metabolic disease, can be inherited in an autosomal recessive (biallelic) or an autosomal dominant (monoallelic) manner. Most of the severe, early-onset, frequently lethal HPP in infants is acquired through recessive inheritance; less severe, later-onset, typically nonlethal HPP phenotypes are acquired through either dominant or recessive inheritance. HPP's variable clinical presentation arises from >400 identified ALPL pathogenic variants with likely variable penetrance, especially with autosomal dominant inheritance. This post hoc analysis investigated the relationship between ALPL variant state (biallelic and monoallelic) and clinical outcomes with asfotase alfa in HPP. Methods Data were pooled from two phase 2, randomized, open-label studies in adolescents and adults with HPP; one study evaluated the efficacy and safety of different doses of asfotase alfa (n = 25), and the other assessed the pharmacodynamics and safety of asfotase alfa (n = 19). Patients were grouped by ALPL variant state (biallelic or monoallelic). Available data from both studies included ALPL pathogenic variant state, Baseline characteristics, HPP-specific medical history, and Baseline TNSALP substrate levels (inorganic pyrophosphate [PPi] and pyridoxal 5′-phosphate [PLP]) concentrations). Clinical outcomes over 5 years of treatment were available from only the efficacy and safety study. Results In total, 44 patients with known variant status were included in the pooled analysis (biallelic, n = 30; monoallelic, n = 14). The most common pathogenic variant was c.571G > A (p.Glu191Lys) in biallelic patients (allele frequency: 19/60) and c.1133A > T (p.Asp378Val) in monoallelic patients (allele frequency: 7/28). Median (min, max) Baseline PPi concentrations were significantly higher in patients with a biallelic vs monoallelic variant state (5.3 [2.2, 12.1] vs 4.3 [3.5, 7.4] μM; P = 0.0113), as were Baseline PLP concentrations (221.4 [62.4, 1590.0] vs 75.1 [28.8, 577.0] ng/mL; P = 0.0022). HPP-specific medical history was generally similar between biallelic and monoallelic patients in terms of incidence and type of manifestations; notable exceptions included fractures, which were more common among monoallelic patients, and delayed walking and bone deformities such as abnormally shaped chest and head and bowing of arms or legs, which were more common among biallelic patients. Data from the efficacy and safety study (n = 19) showed that median PPi and PLP concentrations were normalized over 5 years of treatment in patients with both variant states. Median % predicted distance walked on the 6-Minute Walk Test remained within the normal range for monoallelic patients over 4 years of treatment, and improved from below normal ( Conclusions Although patients with biallelic variants had significantly higher Baseline PPi and PLP levels than monoallelic variants, both groups generally showed similar pretreatment Baseline clinical characteristics. Treatment with asfotase alfa for up to 5 years normalized TNSALP substrate concentrations and improved functional outcomes, with no clear differences between biallelic and monoallelic variant states. This study suggests that patients with HPP have significant disease burden, regardless of ALPL variant state.

Zusammenfassung Hintergrund Die Hypophosphatasie (HPP) ist eine genetische Erkrankung, die durch eine oder mehrere Mutationen im Gen für alkalische Phosphatase (ALP) verursacht wird, verantwortlich für die Kodierung der gewebespezifischen ALP und für den Mineralisierungsprozess. Ziel der Arbeit Bestimmung der Prävalenz der HPP bei rheumatologischen Patienten. Material und Methoden Retrospektive Analyse der Krankenakten aller erwachsener Patienten mit pathologisch erniedrigten gesamt ALP-Werten ( Ergebnisse Bei 60 von 2289 Patienten (2,62 %) zeigten sich pathologisch niedrige ALP-Werte, bei 30 von ihnen (1,31 %) wurden persistierend niedrige ALP-Werte festgestellt. Bei 19 dieser 30 Patienten wurde ein Gentest für ALP-Genmutationen durchgeführt. Sieben der 19 Patienten (36,84 %) hatten HPP-Zeichen (Insuffizienzfrakturen oder schlechter Zahnstatus seit der Kindheit), alle mit pathologischer ALP-Mutation. Drei dieser Patienten (15,78 %) hatten jeweils eine Insuffizienzfraktur mit normwertiger Knochendichtemessung in der Vorgeschichte. Insgesamt 13 von 19 Patienten wiesen (68,42 %) Mutationen im ALP-Gen auf. Interessanterweise wurde keine Assoziation mit einer Chondrokalzinose festgestellt. Diskussion Die HPP scheint eine unterdiagnostizierte Erkrankung mit einem höheren Anteil betroffener Patienten, welche in der Rheumatologie vorstellig werden, zu sein. Daher sollten zukünftige Studien darauf abzielen, ein Diagnostikprotokoll in der klinischen Praxis zu entwickeln.

Pyridoxal 5′-phosphate (PLP), the active cofactor form of vitamin B6 is required by over 160 PLP-dependent (vitamin B6) enzymes serving diverse biological roles, such as carbohydrates, amino acids, hemes, and neurotransmitters metabolism. Three key enzymes, pyridoxal kinase (PL kinase), pyridoxine 5′-phosphate oxidase (PNPO), and phosphatases metabolize and supply PLP to PLP-dependent enzymes through the salvage pathway. In born errors in the salvage enzymes are known to cause inadequate levels of PLP in the cell, particularly in neuronal cells. The resulting PLP deficiency is known to cause or implicated in several pathologies, most notably seizures. One such disorder, PNPO-dependent neonatal epileptic encephalopathy (NEE) results from natural mutations in PNPO and leads to null or reduced enzymatic activity. NEE does not respond to conventional antiepileptic drugs but may respond to treatment with the B6 vitamers PLP and/or pyridoxine (PN). In born errors that lead to PLP deficiency in cells have also been reported in PL kinase, however, to date none has been associated with epilepsy or seizure. One such pathology is polyneuropathy that responds to PLP therapy. Phosphatase deficiency or hypophosphatasia disorder due to pathogenic mutations in alkaline phosphatase is known to cause seizures that respond to PN therapy. In this article, we review the biochemical features of in born errors pertaining to the salvage enzyme’s deficiency that leads to NEE and other pathologies. We also present perspective on vitamin B6 treatment for these disorders, along with attempts to develop zebrafish model to study the NEE syndrome in vivo.

Background Premature exfoliation of the deciduous teeth is a common manifestation in childhood patients with hypophosphatasia (HPP), which is an autosomal inherited disease caused by ALPL mutations. Dysplasia of the cementum, dentin, and alveolar bone has been proposed to be the main reasons for the exfoliation of teeth, while the extraordinarily complex intracellular mechanisms remain elusive. Dental pulp stem cells (DPSCs) have been demonstrated to successfully regenerate functional pulp-dentin-like tissue. Dental pulp cells derived from HPP patients impaired mineralization; however, insight into the deeper mechanism is still unclear. Methods The effects of ALPL on odontoblastic differentiation of DPSCs from HPP patient were assessed by Alizarin Red staining, immunofluorescent staining, Western blot and RT-PCR, and micro-CT assays. Result Here, we found DPSCs from HPP patient exhibited low ALP activity and impaired odontoblastic differentiation. Meanwhile, we found that loss of function of ALPL reduced phosphorylation of GSK3β in DPSCs. While GSK3β rephosphorylation improved odontoblastic differentiation of HPP DPSCs with LiCl treatment. Finally, we demonstrated systemic LiCl injection ameliorated tooth-associated defects in ALPL+/− mice by enhanced phosphorylation of GSK3β in the teeth. Conclusions Our study indicates that ALPL regulates odontoblastic differentiation of DPSCs and provides useful information for understanding how ALPL deficiency led to tooth dysplasia and, ultimately, may inform efforts at improvement tooth defects in HPP patients.

Hypophosphatasia (HPP) is an inherited skeletal disorder that features early exfoliation of primary teeth as a major dental manifestation. A 6Y4M Japanese girl diagnosed with childhood HPP came to our clinic. Deep probing depth for all teeth and severe mobility of primary incisors were observed. At 7Y1M, the mandibular central incisors received a traumatic injury, with no treatment performed and slight mobility observed thereafter. Such traumatic injuries were repeated, thus mouthguards (MGs) to protect weak periodontal tissue were applied, which helped to maintain stable conditions. Use of a MG may be helpful for HPP patients.

The purpose of the present cohort study was a quantitative assessment of the enamel, dentin, and alveolar bone mineral density (BMD) using Cone Beam Computed Tomography (CBCT) scans in patients with X-linked hypophosphatemic rickets (HLHR) and hypophosphatasia (HPP) and a comparison with the data obtained from the control group. Methods and Results: The unrepresentative, non-random sample included 30 CBCT scans of children with genetically and biochemically confirmed XLHR (OMIM #307800) and HPP (OMIM: 146300, 241510, 241500, and 146300). X-ray examination and dental care were carried out in the Radiology Diagnostics Department and Pediatric Dentistry Department at Moscow State University of Medicine and Dentistry named after AI Evdokimov. The mineral density of calcified tissues (enamel, dentin, and alveolar bone) was evaluated using i-CAT Vision TM software options on reconstructed CBCT axial views. The images of all XLHR and HPP patients visualized large pulp chambers with prominent pulp horns extending to the dentin-enamel junction. The present study revealed poor alveolar bone mineralization in patients with HPP and XLHR. Analysis of CBCT scans showed a significant dentine hypodensity in XLHR patients, which may contribute to the emergence of multiple, spontaneous, periapical abscesses spreading rapidly in the jawbone. Conclusion: Data obtained could be used for planning dental treatment of patients with XLHR and HPP.

Hypophosphatasia (HPP) is a rare inherited disease affecting bone and dental mineralization due to loss-of-function mutations in the ALPL gene encoding the tissue nonspecific alkaline phosphatase (TNSALP). Prenatal benign HPP (PB HPP) is a rare form of HPP characterized by in utero skeletal manifestations that progressively improve during pregnancy but often still leave symptoms after birth. Because the prenatal context limits the diagnostic tools, the main difficulty for clinicians is to distinguish PB HPP from perinatal lethal HPP, the most severe form of HPP. We previously attempted to improve genotype phenotype correlation with the help of a new classification of variants based on functional testing. Among 46 perinatal cases detected in utero or in the neonatal period for whose ALPL variants could be classified, imaging alone was thought to clearly diagnose severe lethal HPP in 35 cases, while in 11 cases, imaging abnormalities could not distinguish between perinatal lethal and BP HPP. We show here that our classification of ALPL variants may improve the ability to distinguish between perinatal lethal and PB HPP in utero.

Approximately half of individuals with hypophosphatasemia (low levels of serum alkaline phosphatase) have hypophosphatasia, a rare genetic disease in which patients may have stress fractures, bone and joint pain, or premature tooth loss. We developed a predictive model based on specific biomarkers of this disease to better diagnose this condition. Hypophosphatasemia is a condition in which low levels of alkaline phosphatase (ALP) are detected in the serum. Some individuals presenting with this condition may have a rare genetic disease called hypophosphatasia (HPP), which involves mineralization of the bone and teeth. Lack of awareness of HPP and its nonspecific symptoms make this genetic disease difficult to diagnose. We developed a predictive model based on biomarkers of HPP such as ALP and pyridoxal 5′-phosphate (PLP), because clinical manifestations sometimes are not recognized as symptoms of HPP. We assessed 325,000 ALP results between 2010 and 2015 to identify individuals suspected of having HPP. We performed univariate and multivariate analyses to characterize the relationship between hypophosphatasemia and HPP. Using several machine learning algorithms, we developed several models based on biomarkers and compared their performance to determine the best model. The final cohort included 45 patients who underwent a genetic test. Half (23 patients) showed a mutation of the ALPL gene that encodes the tissue-nonspecific ALP enzyme. ALP (odds ratio [OR] 0.61, 95% confidence interval [CI] 0.3–0.8, p = 0.01) and PLP (OR 1.06, 95% CI 1.01–1.15, p = 0.04) were the only variables significantly associated with the presence of HPP. Support vector machines and logistic regression were the machine learning algorithms that provided the best predictive models in terms of classification (area under the curve 0.936 and 0.844, respectively). Given the high probability of a misdiagnosis, its nonspecific symptoms, and a lack of awareness of serum ALP levels, it is difficult to make a clinical diagnosis of HPP. Predictive models based on biomarkers are necessary to achieve a proper diagnosis. Our proposed machine learning approaches achieved reasonable performance compared to traditional statistical methods used in biomedicine, increasing the likelihood of properly diagnosing such a rare disease as HPP.

Hypophosphatasia (HPP) is a rare inherited metabolic disorder characterized by deficient activity of alkaline phosphatase, causing defective mineralization of bones and teeth. The symptoms vary from no symptoms to stillbirth or skeletal manifestations. Since 2015, asfotase alfa, an enzyme replacement treatment, has been approved for pediatric use in some jurisdictions. We describe the clinical outcome of asfotase alfa therapy in an adolescent patient with childhood HPP. The patient was diagnosed with HPP at 13 months. She had a history of hypertonia and failure to thrive from age 3 months. During childhood the patient experienced chronic skeletal pain, requiring daily use of analgesics and school absences. Her plasma pyridoxal-5-phosphate was elevated at >2500 mmol/L, phosphoethanolamine at 11 μM, and ALP decreased at 25 U/L. On the visual analog scale (VAS), a scale used to determine pain intensity, she stated an average of 7 (maximum 10) at age 13. She had no abnormalities on radiography. At age 13 the patient was started on asfotase alfa 1 mg/kg given subcutaneously 6 times weekly. Three months after treatment the patient had a decreased P-pyridoxal-5-phosphate level of 41 mmol/L, used fewer analgesics, and a lower average VAS-score. At every follow-up, she continued to exhibit improved biochemical values, along with lower VAS-scores. In conclusion, asfotase alfa significantly improved the patient's quality of life. This case suggests an association between children with HPP without radiographic abnormalities, but a debilitating pain phenotype, and a significant pain reduction on enzyme replacement therapy. Thus, this therapy should be considered in such patients.

In recent years, new treatment options for both common and rare bone diseases have become available. The sclerostin antibody romosozumab is the most recently approved drug for the therapy of postmenopausal osteoporosis. Its anabolic capacity makes it a promising treatment option for severe osteoporosis. Other sclerostin antibodies for the treatment of rare bone diseases such as osteogenesis imperfecta are currently being investigated. For rare bone diseases such as X‑linked hypophosphatemia (XLH) and hypophosphatasia (HPP), specific therapies are now also available, showing promising data in children and adults with a severe disease course. However, long-term data are needed to assess a sustained benefit for patients.Neue therapeutische Möglichkeiten zur Therapie der Osteoporose, aber auch seltener Knochenerkrankungen stehen neuerdings zu Verfügung. Der Sclerostin-Antikörper Romosozumab wurde unlängst zur Behandlung der postmenopausalen Osteoporose zugelassen. Durch seine osteoanabole Wirkung scheint Romosozumab eine vielversprechende Therapieoption der schweren Osteoporose zu sein. Andere Sclerostin-Antikörper werden derzeit bei seltenen Knochenerkrankungen wie der Osteogenesis imperfecta untersucht. Für den Phosphatdiabetes („X-linked hypophosphatemia“, XLH) und die Hypophosphatasie (HPP) stehen nun spezifische Therapien zur Verfügung, die in den bisherigen Studien überzeugende Ergebnisse zeigten. Langzeitdaten sind jedoch erforderlich, um das Risiko-Nutzen-Profil abschätzen zu können.

Hypophosphatasia (HPP) is a rare hereditary metabolic disease resulting from the loss-of-function mutation in the ALPL gene encoding tissue-nonspecific alkaline phosphatase (ALP). Clinical presentations are polymorphic and manifest themselves differently depending on the age of disease onset and severity. The occurrence of mild disease, including adult HPP, is challenging to assess due to the high heterogeneity of clinical signs and a lower diagnosis rate. Doctors’ awareness of HPP is the fundamental factor affecting its detection rate. This paper reviews the conclusions of the Expert Council on HPP diagnosis and potentialities to improve diagnosis. Ten experts from various Russian regions participated in panel sessions. Each member shared the experience and established practice on the diagnosis of orphan diseases in his/her region and gave suggestions to optimize the diagnostic approach to HPP. The result was the development of a management algorithm and routing of patients from identifying symptoms to decision making on prescribing enzyme-replacement therapy and subsequent follow-up at every level of medical care . KEYWORDS: hypophosphatasia, alkaline phosphatase, orphan diseases, ALPL, enzyme-replacement therapy, routing. FOR CITATION: Zakharova E.Yu., Varlamova T.V., Voronin S.V. et al. Unsolved diagnostic issues of hypophosphatasia: Expert Council. Russian Medical Inquiry. 2021;5(9):605–614 (in Russ.). DOI: 10.32364/2587-6821-2021-5-9-605-614.

Hypophosphatasia (HPP) is a rare skeletal dysplasia characterized by impaired bone mineralization, caused by loss-of-function mutations in the tissue-nonspecific alkaline phosphatase (TNSALP) gene. Enzyme replacement therapy (ERT) by administration of asfotase alfa was reported to improve the survival rate, bone mineralization, and short stature in the severe form of HPP. However, the effect of asfotase alfa in improving the skeletal phenotypes for the mild form of HPP has not been elucidated. We report a case with perinatal benign HPP who had compound heterozygous mutations of p.F327L and p.R30X in the TNSALP gene. No hypomineralization was seen in the radiographs from the neonatal period, but bowing of the femurs and ulnares bilaterally was persistent. ERT was administered during the age of 7.8 to 10.8 yr, although there was an interruption in the treatment for one year. The bowed femurs and ulnares were not improved by the treatment with asfotase alfa at the age of 10.8 yr. Bone mineral density of the lumbar spine was between –0.5 and –1.0 of the z-score, and the patient’s height was about –2.0 SD during the treatment. Asfotase alfa might have a limited effect in improving the bowed limbs in perinatal benign hypophosphatasia.

he authors present the latest data on the hypophosphatasia (HPP) management in children. Hypophosphatasia is a rare genetic disease caused by deficiency of tissue-specific alkaline phosphatase due to mutation in the ALPL gene. The article covers all the features of epidemiology, etiology and pathogenesis, detailed stages of differential diagnostics. Treatment guidelines for pediatric patients are provided, they are based on the principles of evidence-based medicine. Special attention was given to the only effective method of hypophosphatasia management —enzyme replacement therapy (ERT). This material is the clinical guideline draft for the management of patients with hypophosphatasia prepared by the Union of Pediatricians of Russia and the Association of Medical Geneticists.

Introduction: Hypophosphatasia is a systemic bone disease characterized by inhibition of bone mineralization due to mutations in the ALPL gene that results in a deficiency of tissue nonspecific alkaline phosphatase. The perinatal form is the most severe. In the past, this form was lethal, although human recombinant enzyme replacement therapy has now been developed and licensed, which improves survival. Perinatal hypophosphatasia is usually suggested on antenatal ultrasonography with undermineralization of the long bones, skull, and thoracic cavity. In the UK, antenatal ultrasonography for fetal anomalies is conducted at mid-gestation (i.e., 18–21 weeks gestational age), and if normal, no further routine scans are performed. Usually, this would identify abnormalities in bone mineralization suggestive of perinatal hypophosphatasia. Cases: We describe 2 cases of perinatal hypophosphatasia where mid-gestation ultrasonography was normal. In the first case, where a previous pregnancy had been terminated for perinatal hypophosphatasia, third trimester ultrasonography revealed skeletal features of hypophosphatasia. In the second case, the diagnosis of perinatal hypophosphatasia was made only immediately after birth. Conclusion: We conclude that serial antenatal ultrasonography or antenatal genetic testing should be considered in all pregnancies with a positive family history of hypophosphatasia, as mid-gestation ultrasonography cannot reliably exclude perinatal hypophosphatasia. This is especially important given that effective enzyme replacement therapy is now available.

Hypophosphatasia (HPP) is an inborn error of metabolism caused by loss-of-function mutations in the biomineralization-associated alkaline phosphatase gene, encoding tissue-nonspecific alkaline phosphatase (TNSALP). Symptoms include skeletal hypomineralization and extra-skeletal manifestations such as pyridoxine (B6)-responsive seizures due to impaired cerebral B6 passage. Since the introduction of enzyme replacement therapy (ERT), skeletal manifestations and B6-responsive seizures were reported to improve significantly. Nevertheless, there is an increasing evidence of B6-independent neurological manifestation of HPP including HPP-associated encephalopathy. Here, we present for the first time the brain alterations of an infant with neonatal HPP who died of neurological complications at the age of 5 months despite early initiation of ERT. CSF analysis showed normal concentrations of biogenic amines reflecting sufficient intracellular B6 availability. Postmortem histopathology revealed severe, localized affection of the cerebral cortex including cortical lesions in layers 2 and 3 in direct proximity to TNSALP-expressing neurons and hippocampal sclerosis. Our findings confirm that TNSALP deficiency may lead to a severe encephalopathy. We hypothesize that HPP-associated encephalopathy resistant to currently available ERT may develop in addition and probably independently of typical B6-responsive seizures in some patients. Prospective, controlled studies with close neurological follow-up including brain imaging are needed to identify patients at risk for severe neurological symptoms despite ERT.

Alkaline phosphatase activity is a parameter included in biochemical liver test. These isoenzymes are of various cellular origin inducing physiological variations on age and sex. The alkaline phosphatase activity standardization as well as numerous international studies have made it possible to standardize the pediatric reference values. The hyperphosphatasemia etiologies are very well know but the hypophosphatasemia are hardly explored and can allow the diagnosis of pathologies including hypophosphatasia, a rare treatable disease.

Infants presenting with multiple fractures without a plausible accident history need to be evaluated for child abuse or underlying predisposing conditions such as osteogenesis imperfecta and hypophosphatasia. We present a case of infantile hypophosphatasia with multiple unexplained fractures but otherwise normal radiographs in the setting of biochemical and genetic evidence of hypophosphatasia. Standard screening tests for hypophosphatasia include serum alkaline phosphatase level and genetic testing. Despite the presented case’s positive biochemical and genetic testing, the case did not have any other radiologic finding suggesting infantile hypophosphatasia, such as severe bone mineralization deficits and rickets. While patients with hypophosphatasia can have increased bone fragility, this has been reported in the context of radiologic abnormalities of the skeleton. Thus, this case is potentially the first reported infantile hypophosphatasia case presenting with no findings of rickets on radiographs, raising concern that the fractures and especially the radius head dislocation might be due to physical abuse.

Hypophosphatasia (HPP) is a rare inborn error of metabolism due to a decreased activity of tissue nonspecific alkaline phosphatase (TNSALP). As the onset and severity of HPP are heterogenous, it can be challenging to determine the pathogenicity of detected rare ALPL variants in symptomatic patients. We aimed to characterize patients with rare ALPL variants to propose which patients can be diagnosed with adult HPP. We included 72 patients with (1) clinical symptoms of adult HPP or positive family history and (2) low TNSALP activity and/or high pyridoxal 5′-phosphate (PLP) levels, who underwent ALPL gene sequencing. The patients were analyzed and divided into three groups depending on ALPL variant pathogenicity according to the classification of the American College of Medical Genetics and Genomics (ACMG). Reported pathogenic (n = 34 patients), rare (n = 17) and common (n = 21) ALPL variants only were found. Muscular complaints were the most frequent symptoms (> 80%), followed by bone affection (> 50%). Tooth involvement was significantly more common in patients with pathogenic or rare ALPL variants. Seven rare variants could be classified as likely pathogenic (ACMG class 4) of which five have not yet been described. Inconclusive genetic findings and less specific symptoms make diagnosis difficult in cases where adult HPP is not obvious. As not every pathogenic or rare ALPL variant leads to a manifestation of HPP, only patients with bone complications and at least one additional complication concerning teeth, muscle, central nervous and mental system, repeated low TNSALP activity and high PLP levels should be diagnosed as adult HPP if rare ALPL gene variants of ACMG class 4 or higher support the diagnosis.

We report clinical and radiological features of a patient born with an isolated skull malformation of caput membranaceum and partial bicoronal craniosynostosis with a novel, de novo heterozygous missense variant in ZIC1 [NM_003412.3:c.1183C>G, p.(Pro395Ala)]. Caput membranaceum, or boneless skull, is a rare manifestation of skull ossification defect. It can result from an isolated, enlarged parietal foramina or it can present as part of skeletal dysplasia syndromes associated with poor mineralization such as hypophosphatasia, osteogenesis imperfecta type II, and Saethre-Chotzen syndrome. Their causative genes are well described. ZIC1, Zinc Finger protein of the cerebellum 1 (OMIM #600470) belongs to ZIC family genes, each encoding a Cys2 His2-type zinc finger domain-containing transcription factors. Recent studies have shown that pathogenic variants in ZIC1 have deleterious effect in developing human central nerves system and skull bone. ZIC1 related clinical conditions are reported and include cerebellum malformation, Dandy-Walker malformation, spinal dysraphism, microcephaly, and craniosynostosis with associated intellectual disability. To-date, there is no report of pathogenic variant in ZIC1 causing isolated caput membranaceum. Our observation adds to the clinical spectrum of ZIC1 related skull malformation.

Summary In adult hypophosphatasia (HPP) patients, elevated lumbar spine dual X-ray absorptiometry (DXA) values are associated with markers of disease severity and disease-specific fracture risk while femoral bone mineral density (BMD), being largely unaffected by the disease severity, may still be useful to monitor other causes of increased fracture risk due to low BMD. Introduction Hypophosphatasia (HPP) is a rare inherited metabolic disorder due to deficient activity of the tissue-nonspecific alkaline phosphatase (TNAP). Clinical manifestation in adult HPP patients is manifold including an increased risk for fractures, but data regarding clinical significance of DXA measurement and associations with fracture risk and disease severity is scarce. Methods Retrospective single-center analysis of DXA scans in patients with confirmed HPP (documented mutation, clinical symptoms, low alkaline phosphatase activity). Further data evaluation included disease-related fractures, laboratory results (alkaline phosphatase, pyridoxalphosphate, phosphoethanolamine), and medical history. Results Analysis included 110 patients (84 female, mean age of 46.2 years) of whom 37.3% (n = 41) were harboring two mutations. Average T-Score level at the lumbar spine was − 0.1 (SD 1.9), and mean total hip T-Score was − 1.07 (SD 0.15). Both lower ALP activity and higher substrate levels (pyridoxalphosphate and phosphoethanolamine) were significantly correlated with increased lumbar spine T-Score levels (p < 0.001) while BMD at the hip was not affected by indicators of disease severity. Increased lumbar spine BMD was significantly associated with an increased risk for HPP-related fractures, prevalent in 22 (20%) patients (p < 0.001) with 21 of them having biallelic mutations. Conclusion BMD in adult HPP patients is not systematically reduced. Conversely, increased lumbar spine BMD appears to be associated with severely compromised mineralization and increased risk for HPP-related fractures while BMD at the hip appears unaffected by indicators of disease severity, suggesting suitability of this anatomic location for assessing and discerning disorders with increased fracture risk owing to reduced BMD like osteoporosis. Trial registration number German register for clinical studies (DRKS00014022) Date of registration 02/10/2018 – retrospectively registered Electronic supplementary material The online version of this article (10.1007/s00198-020-05612-9) contains supplementary material, which is available to authorized users.

PURPOSE OF REVIEW: The skeletal system provides an important role to support body structure and protect organs. The complexity of its architecture and components makes it challenging to deliver the right amount of the drug into bone regions, particularly avascular cartilage lesions. In this review, we describe the recent advance of bone-targeting methods using bisphosphonates, polymeric oligopeptides, and nanoparticles on osteoporosis and rare skeletal diseases. RECENT FINDINGS: Hydroxyapatite (HA), a calcium phosphate with the formula Ca(10)(PO(4))(6)(OH)(2), is a primary matrix of bone mineral that includes a high concentration of positively charged calcium ion and is found only in bone. This unique feature makes HA a general targeting moiety to the entire skeletal system. We have applied bone-targeting strategy using acidic amino acid oligopeptides into lysosomal enzymes, demonstrating the effects of bone-targeting enzyme replacement therapy and gene therapy on bone and cartilage lesions in inherited skeletal disorders. Virus or no-virus gene therapy using techniques of engineered capsid or nanomedicine has been studied preclinically for skeletal diseases. SUMMARY: Efficient drug delivery into bone lesions remains an unmet challenge in clinical practice. Bone targeting therapies based on gene transfer can be potential as new candidates for skeletal diseases.

Background Perinatal and infantile hypophosphatasia (HPP) are associated with respiratory failure and respiratory complications. Effective management of such complications is of key clinical importance. In some infants with HPP, severe tracheobronchomalacia (TBM) contributes to respiratory difficulties. The objective of this study is to characterize the clinical features, investigations and management in these patients. Methods We report a case series of five infants with perinatal HPP, with confirmed TBM, who were treated with asfotase alfa and observed for 3–7 years. Additionally, we reviewed respiratory function data in a subgroup of patients with perinatal and infantile HPP included in the clinical trials of asfotase alfa, who required high-pressure respiratory support (positive end-expiratory pressure [PEEP] ≥6 cm H2O and/or peak inspiratory pressure ≥18 cm H2O) during the studies. Results The case series showed that TBM contributed significantly to respiratory morbidity, and prolonged respiratory support with high PEEP was required. However, TBM improved over time, allowing weaning of all patients from ventilator use. The review of clinical trial data included 20 patients and found a high degree of heterogeneity in PEEP requirements across the cohort; median PEEP was 8 cm H2O at any time and some patients presented with high PEEP (≥8 cm H2O) over periods of more than 6 months. Conclusion In infants with HPP presenting with persistent respiratory complications, it is important to screen for TBM and initiate appropriate respiratory support and treatment with asfotase alfa at an early stage. Trial registration ClinicalTrials.gov numbers: NCT00744042, registered 27 August 2008; NCT01205152, registered 17 September 2010; NCT01176266, registered 29 July 2010.

Purpose of review The goal of this review is to give an overview of diagnosis and up-to-date management of major pediatric metabolic bone diseases that are associated with bone fragility, including nutritional rickets, hypophosphatemic rickets, osteogenesis imperfecta, Ehlers--Danlos syndrome, Marfan's syndrome, hypophosphatasia, osteopetrosis and skeletal fluorosis. Recent findings During the past decade, a number of advanced treatment options have been introduced and shown to be an effective treatment in many metabolic bone disorders, such as burosumab for hypophosphatemic rickets and asfotase alfa for hypophosphatasia. On the other hand, other disorders, such as nutritional rickets and skeletal fluorosis continue to be underrecognized in many regions of the world. Genetic disorders of collagen-elastin, such as osteogenesis imperfecta, Ehlers--Danlos syndrome and Marfan's syndrome are also associated with skeletal fragility, which can be misdiagnosed as caused by non-accidental trauma/child abuse. Summary It is essential to provide early and accurate diagnosis and treatment for pediatric patients with metabolic bone disorders in order to maintain growth and development as well as prevent fractures and metabolic complications.

Using genetic, clinical, biochemical, and radiographic assessment and bioinformatic approaches, we present an unusual case of adult HPP caused by a novel de novo heterozygous nonsense mutation in the alkaline phosphatase (ALPL). Hypophosphatasia (HPP) is caused by genetic alterations of the ALPL gene, encoding the tissue-nonspecific isozyme of alkaline phosphatase (TNSALP). Here, the purpose was to perform clinical and molecular investigation in a 36-year-old Caucasian woman suspected to present adult HPP. Medical and dental histories were obtained for the proposita and family members, including biochemical, radiographic, and dental assessments. ALPL mutational analysis was performed by the Sanger sequencing method, and the functional impact prediction of the identified mutations was assessed by bioinformatic methods. We identified a novel heterozygous nonsense mutation in the ALPL gene (NM_000478.6:c.768G>A; W[TGG]>*[TGA]) associated with spontaneous vertebral fracture, severe back pain, musculoskeletal pain, low bone density, and short-rooted permanent teeth loss. Functional prediction analysis revealed that the Trp256Ter mutation led to a complete loss of TNSALP crown domain and extensive loss of other functional domains (calcium-binding domain, active site vicinity, and zinc-binding site) and over 60% loss of homodimer interface residues, suggesting that the mutant TNSALP molecules are nonfunctional and form unstable homodimers. Genotyping of the ALPL in the proposita’s parents, sister, and niece revealed that in this case, HPP occurred due to a de novo mutation. The present study describes a novel genotype-phenotype and structure-function relationship for HPP, contributing to a better molecular comprehension of HPP etiology and pathophysiology.

SUMMARY Hypophosphatasia (HPP) is a rare disease with a high mortality rate in its severe forms. It is caused by mutations within the gene encoding the tissue-nonspecific alkaline phosphatase (TNSALP), an enzyme responsible for bone mineralization. In 2015, the Food and Drug Administration approved the use of asfotase alfa, the first medication showing benefit in the treatment of HPP. We describe a case with a 2-year follow-up of the first Brazilian child treated with asfotase alfa. A 5-year-old boy, born to consanguineous parents, was diagnosed with HPP at the age of 20 months. During prenatal ultrasonography, polyhydramnios and shortening of long bones were detected. After birth, he presented delayed motor development, repeated respiratory infections, and bone deformities. At the age of 2 years and 8 months, he started walking and had already lost his primary teeth. He had reduced levels of alkaline phosphatase (ALP), elevated levels of pyridoxal 5’-phosphate (PLP), and a p.Ala33Val (c.98C>T) missense mutation in homozygosis in the TNSALP gene. His parents and sister also had reduced ALP levels, high PLP levels, and the same mutation in heterozygosis. His father and sister were healthy, and his mother was diagnosed with rickets in childhood, which resulted in short physical stature and lower limb deformities. The patient was started on asfotase alfa at the age of 2 years and 10 months. After 2 years of treatment, he improved his motor skills, had no further episodes of severe respiratory infection, and showed improved radiological findings of rickets, without any severe side effect.

Beyond its functions in locomotion, support and protection of vital organs, bone also interacts with other organs to adjust mineral balance in response to physiological requirements. Bone remodelling is a continuous process of bone resorption and formation for the purpose of maintaining healthy bone mass and growth. Any derangement in this process can cause bone disorders with important clinical consequences. The most prominent features of bone diseases in children include early bone fractures, deformities and pain, which can persist and worsen later in life if an accurate and timely diagnosis is not achieved. Biochemical and genetic testing usually help to discriminate the aetiology of the disease, which determines the subsequent management and follow-up. This review focuses on major genetic metabolic bone diseases in children, their pathophysiological mechanisms, the potential therapeutic interventions and the possible consequences in adulthood of the disease and its treatments.

The most frequent dental signs of hypophosphatasia in children are premature loss of primary teeth, decrease in height of alveolar bone, and malocclusions. Enzyme replacement therapy with Asfotase alfa might be associated with stabilization of dental status.

Hypophosphatasia, a rare genetic disease affecting bone metabolism, is characterized by decreased activity of tissue non-specific alkaline phosphatase (TNAP). The gene encoding TNAP (ALPL) has considerable allelic heterogeneity, which could explain different degrees of enzyme activity resulting in a wide clinical variability. We report the case of a preterm newborn in whom a corneal opacity was detected at birth. Blood tests performed to investigate this finding showed low alkaline phosphatase concentrations. The corneal opacity disappeared within a week but alkaline phosphatase remained persistently low. With persistently decreased levels of alkaline phosphatase, upon suspicion of hypophosphatasia, plain radiography detected changes suggestive of rickets. Sequencing of the ALPL gene revealed a heterozygous variant that has not been described in the literature to date. Our patient’s condition may be an atypical neonatal form of the syndrome, with a mild phenotype, very different from the classic neonatal form, which can lead to severe skeletal disease and respiratory failure. However, it could also be an early diagnosis of the childhood form, which is associated with a better prognosis.

Low serum alkaline phosphatase (sALP)-hypophosphatasemia-is a characteristic of hypophosphatasia (HPP), but related to several clinical conditions. Here, we evaluated the frequency, persistency and the etiology of hypophosphatasemia in children. In retrospective analyses of sALP measurements from children, evaluated according to in-house constructed age- and sex-specific reference ranges, patients with no normal sALP measurement (Unresolved hypophosphatasemia) were invited for reanalysis. Prospectively, ALP substrates, pyridoxal-5-phosphate (PLP), and phosphoethanolamine (PEA) were measured in patients with persistent hypophosphatasemia. Radiographs and ALPL gene sequencing for HPP were performed to the cases with elevated PEA and/or PLP. From 130,340 sALP measurements of 93,162 patients, hypophosphatasemia was detected in 1404 samples from 867 patients (0.9%). Among them, 745 had at least one normal sALP values in laboratory records, grouped as transient hypophosphatasemia. 75 out of 122 patients with unresolved hypophosphatasemia could be reanalyzed for sALP, of whom PLP and PEA measurements were required in 37 due to persistent hypophosphatasemia. Both PEA and PLP were elevated in 4 patients, and ALPL gene analysis showed heterozygous mutations in 3 patients and homozygous in 1 patient. Elevated PEA with normal PLP were detected in 3 patients, and one had a heterozygous ALPL mutation. Anemia was the most common diagnosis, and upper respiratory tract infections and chronic diseases were more common in transient and unresolved hypophosphatasemia, respectively. In conclusion, reflected persistent hypophosphatasemia frequency was 1/1552 (0.06%) in this large pediatric cohort and, ALPL gene mutations were detected in 13.5% (5/37) of the studied cases. Although biochemical hypophosphatasemia is not uncommon, clinically significant HPP is rare.

Objective of the Paper: to describe a clinical case of paediatric hypophosphatasia (HPP) and identify clinical signs, most characteristic of the paediatric HPP form. Key Points. HPP is an congenital rickets-like disease caused by reduced activity of tissue-nonspecific alkaline phosphatase (ALP). According to the time of manifestation, there are perinatal, infant, paediatric, and adult HPPs. The article describes a clinical case of paediatric HPP in a 3.5-year old boy. HPP was diagnosed due to reduced ALP and characteristic X-ray findings. The diagnosis was confirmed with DNA testing: compound heterozygous mutation in с.571 G>A/с.144_148dup of ALPL was found. Conclusion. Typical findings in paediatric HPP are growth retardation and muscular hypotonia, motor retardation; gait disturbances, myalgia, marked fatigue causing limited period of walking; rachitic deformations, premature loss of milk teeth with unchanged roots, respiratory disturbances, and frequent bronchopulmonary disorders. Keywords: hypophosphatasia, children, alkaline phosphatase.

This article provides an overview of the current knowledge on hypophosphatasia—a rare genetic disease of very variable presentation and severity—with a special focus on adolescents and adults. It summarizes the available information on the many known mutations of tissue-nonspecific alkaline phosphatase (TNSALP), the epidemiology and clinical presentation of the disease in adolescents and adults, and the essential diagnostic clues. The last section reviews the therapeutic approaches, including recent reports on enzyme replacement therapy (EnzRT).

S.A. Boykov1, I.Yu. Chernyak1, N.S. Shatokhina1, E.Yu. Gurkina2, N.A. Borodina3, E.F. Chelabova3, S.A. Epoeva3 1Children’s Regional City Hospital, Krasnodar, Russian Federation 2V.A. Almazov National Medical Research Center, St. Petersburg, Russian Federation 3Children’s Hospital of the city of Armavir, Armavir, Russian Federation Hypophosphatasia (HPP) is a rare multisystem inherited metabolic disorder caused by mutations in ALPL gene that encodes tissue nonspecific alkaline phosphatase responsible for bone mineralization. HPP is characterized by impaired bone mineralization, skeletal abnormalities, and systemic manifestations which result in significant morbidity and mortality. Clinical presentations of HPP vary greatly. Early (perinatal and infantile) HPP is characterized by the most severe symptoms, i.e., respiratory and neurological disorders are of crucial importance being the leading causes of death. Progressive skeletal impairment, rickets-like deformities, reduced mobility, and severe disability are typical of childhood-onset HPP. The biochemical hallmark of HPP is low alkaline phosphatase (ALP) activity. HPP diagnosis is verified by clinical symptoms in combination with persistently low ALP activity (adjusted for age and sex). Molecular genetic test to identify ALPL gene mutation is performed as needed. Three case reports addresses authors’ experience with the diagnosis and treatment for HPP. Keywords: hypophosphatasia, case series, alkaline phosphatase, impaired bone mineralization, asfotase alfa. For citation: Boykov S.A., Chernyak I.Yu., Shatokhina N.S. et al. Hypophosphatasia in children. Three faces of one disease. Russian Journal of Woman and Child Health. 2020;3(2):136–141. DOI: 10.32364/2618-8430-2020-3-2-136-141.

Hypophosphatasia (HPP) is a rare genetic skeletal disorder that occurs due to mutation in the ALPL gene. It is characterized by defective bone and teeth mineralization. Odontohypophosphatasia is the mildest form of HPP that affects only the dental tissues, manifests as early exfoliation of teeth, defective cementum formation, reduced alveolar bone height, and enlarged pulp chamber. We report a case of an 8-year-old female who presented only with dental findings of HPP. HPP was suspected due to reduced serum alkaline phosphatase level, reduced alveolar bone height, and enlarged pulp chamber. The cemental defects were identified by the ground section of the exfoliated tooth and measured using Image J software. Thus, we arrived at the final diagnosis of Odontohypophosphatasia.

Skeletal mineralization is initiated in matrix vesicles (MVs), the small extracellular vesicles derived from osteoblasts and chondrocytes. Calcium and inorganic phosphate (Pi) taken up by MVs form hydroxyapatite crystals, which propagate on collagen fibrils to mineralize the extracellular matrix. Insufficient calcium or phosphate impairs skeletal mineralization. Because active vitamin D is necessary for intestinal calcium absorption, vitamin D deficiency is a significant cause of rickets/osteomalacia. Chronic hypophosphatemia also results in rickets/osteomalacia. Excessive action of fibroblast growth factor 23 (FGF23), a key regulator of Pi metabolism, leads to renal Pi wasting and impairs vitamin D activation. X-linked hypophosphatemic rickets (XLH) is the most common form of hereditary FGF23-related hypophosphatemia, and enhanced FGF receptor (FGFR) signaling in osteocytes may be involved in the pathogenesis of this disease. Increased extracellular Pi triggers signal transduction via FGFR to regulate gene expression, implying a close relationship between Pi metabolism and FGFR. An anti-FGF23 antibody, burosumab, has recently been developed as a new treatment for XLH. In addition to various forms of rickets/osteomalacia, hypophosphatasia (HPP) is characterized by impaired skeletal mineralization. HPP is caused by inactivating mutations in tissue-nonspecific alkaline phosphatase, an enzyme rich in MVs. The recent development of enzyme replacement therapy using bone-targeting recombinant alkaline phosphatase has improved the prognosis, motor function, and quality of life in patients with HPP. This links impaired skeletal mineralization with various conditions, and unraveling its pathogenesis will lead to more precise diagnoses and effective treatments.

Hypophosphatasia (HPP) is highly variable in clinical expression and is generally classified into six subtypes. Although it would be beneficial to be able to predict the clinical course from the ALPL genotype, studies on this issue are limited. Here, we aimed to clarify the features of Japanese HPP and the relationships between genotype and clinical manifestations. We analyzed 98 unrelated Japanese patients to investigate the percentage of each clinical form, frequently detected mutations, and the relationship between the genotype and phenotype. Some of the identified mutants were characterized by transfection experiments. Perinatal severe form was the most frequent (45.9%), followed by perinatal benign form (22.4%). Among the 196 alleles, p.Leu520ArgfsX86 (c.1559delT) was detected in 89 alleles, and p.Phe327Leu (c.979T>C) was identified in 23 alleles. All of the homozygotes for p.Leu520ArgfsX86 were classified into perinatal severe form, and patients carrying p.Phe327Leu in one of the alleles were classified into perinatal benign or odonto HPP. Twenty of the 22 patients with perinatal benign HPP were compound heterozygous for p.Phe327Leu and another mutation. Most patients with odonto HPP were found to be monoallelic heterozygotes for dominant-negative mutations or compound heterozygotes with mutants having residual activity. The high prevalence of p.Leu520ArgfsX86 and p.Phe327Leu mutations might underlie the high rate of perinatal severe and perinatal benign forms, respectively, in Japanese HPP. Although ALPL genotyping would be beneficial for predicting the clinical course to an extent, the observed phenotypical variability among patients sharing the same genotypes suggests the presence of modifiers.

Objective To review the diagnosis and clinical course of a woman with hypophosphatasia who is being treated with newly approved enzyme replacement therapy, asfotase alfa. Methods Clinical and laboratory data are presented. Results This is a unique report of a woman with debilitating adult-onset hypophosphatasia who was successfully diagnosed with low alkaline phosphatase (ALP) levels and elevated vitamin B6 levels. Treatment with asfotase alfa resolved her chronic bony pain symptoms and quadrupled her daily pedometer step count. Furthermore, whole body scans before and after treatment showed less focal uptake overall, suggesting fracture healing after enzyme replacement therapy. Conclusion Improvement in patient reported symptoms, daily pedometer count, and whole body scans was noted after treatment of adult-onset hypophosphatasia with asfotase alfa enzyme replacement therapy. The significance of increased ALP levels after treatment is currently unknown.

Hypophosphatasia (HPP) is a rare hereditary metabolic disease characterized by defective bone and dental mineralization, systemic complications that lead to disability of patients. HPP is classified into six forms according to the age of onset and severity of its clinical picture. The disease is caused by a reduced activity of the tissue nonspecific alkaline phosphatase (TNSALP) and elevated concentrations of pyrophosphates. Asfotase alfa is the only pathogenetic enzyme replacement therapy with recombinant human bone-targeted TNSALP approved for treatment of patients with perinatal, infantile and juvenile‐onset HPP. This treatment is associated with improved skeletal mineralization, respiratory function and overall survival in infants and young children with life-threatening hypophosphatasia. The world experience in application of recombinant alkaline phosphatase in adults is very limited. We present a clinical case that describes the first Russian experience in the use of asfotase alfa in an 18-year-old patient with late diagnosis of childhood-onset HPP.