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Twenty-five years ago, a pathogenic variant of the phosphate-regulating endopeptidase homolog X-linked (PHEX) gene was identified as the cause of X-linked hypophosphatemic rickets (XLH). Subsequently, the overproduction of fibroblast growth factor 23 (FGF23) due to PHEX defects has been found to be associated with XLH pathophysiology. However, the mechanism by which PHEX deficiency contributes to the upregulation of FGF23 and the function of PHEX itself remain unclear. To date, over 700 pathogenic variants have been identified in patients with XLH, and functional assays and genotype–phenotype correlation analyses based on pathogenic variant data derived from XLH patients have been reported. Genetic testing for XLH is useful for the diagnosis. Not only have single-nucleotide variants causing missense, nonsense, and splicing variants and small deletion/insertion variants causing frameshift/non-frameshift alterations been observed, but also gross deletion/duplication variants causing copy number variants have been reported as pathogenic variants in PHEX. With the development of new technologies including next generation sequencing, it is expected that an increasing number of pathogenic variants will be identified. This chapter aimed to summarize the genotype of PHEX and related analyses and discusses the pathophysiology of PHEX defects to seek clues on unsolved questions.

Background McCune-Albright syndrome (MAS) is caused by postzygotic somatic mutations of the GNAS gene. It is characterized by the clinical triad of fibrous dysplasia, cafe-au-lait skin spots, and endocrinological dysfunction. Myriad complications in MAS, including hepatobiliary manifestations, are also reported. Case summary This is a case of a 4-year-old boy who presented with MAS with neonatal cholestasis. He was suspected to have Alagille syndrome due to neonatal cholestasis with intrahepatic bile duct paucity in liver biopsy, peripheral pulmonary artery stenosis, and renal tubular dysfunction. By the age of 2 years, his cholestatic liver injury gradually improved, but he had repeated left femoral fractures. He did not exhibit endocrinological abnormality or cafe-au-lait skin spots. However, MAS was suspected due to fibrous dysplasia at the age of 4 years. No mutation was identified in the GNAS gene in the DNA isolated from the peripheral blood, but an activating point mutation (c.601C>T, p.Arg201Cys) was observed in the DNA extracted from the affected bone tissue and that extracted from the formalin-fixed paraffin-embedded liver tissue, which was obtained at the age of 1 mo. Conclusion MAS should be considered as a differential diagnosis for transient cholestasis in infancy.

An elevated serum alkaline phosphatase (ALP) level is one of the markers for the presence of rickets in children, but it is also associated with bone formation. However, its role in diagnosing genu varum in pediatric patients with vitamin D-deficient rickets is still unknown. To clarify the role of the serum ALP level in assessing the severity of genu varum, we retrospectively investigated this issue statistically using data on rickets such as serum intact parathyroid hormone (iPTH), 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, ALP, the level of creatinine as the percentage of the median according to age (%Cr), and the metaphyseal diaphyseal angle (MDA) in the lower extremities as an index of the severity of genu varum. A multiple regression analysis revealed that log ALP and %Cr values were negatively associated with MDA values. The former association was also confirmed by a linear mixed model, while iPTH was positively associated with MDA by path model analysis. To elucidate the association of ALP with MDA in the presence of iPTH, we investigated three-dimensional figures by neural network analysis. This indicated the presence of a biphasic association of ALP with MDA: the first phase increases while the second decreases MDA. The latter phenomenon is considered to be associated with the increase in bone formation due to the mechanical stress loaded on the lower extremities. These findings are important and informative for pediatricians to understand the significance of the serum ALP level in pediatric patients with genu varum caused by vitamin D deficiency.

Paget's disease (PD) is characterized by increased numbers of abnormal osteoclasts (OCLs) that drive exuberant bone formation, but the mechanisms responsible for the increased bone formation remain unclear. We previously reported that OCLs from 70% of PD patients express measles virus nucleocapsid protein (MVNP), and that transgenic mice with targeted expression of MVNP in OCLs (MVNP mice) develop bone lesions and abnormal OCLs characteristic of PD. In this report, we examined if OCL‐derived sphingosine‐1‐phosphate (S1P) contributed to the abnormal bone formation in PD, since OCL‐derived S1P can act as a coupling factor to increase normal bone formation via binding S1P‐receptor‐3 (S1PR3) on osteoblasts (OBs). We report that OCLs from MVNP mice and PD patients expressed high levels of sphingosine kinase‐1 (SphK‐1) compared with wild‐type (WT) mouse and normal donor OCLs. SphK‐1 production by MVNP‐OCLs was interleukin‐6 (IL‐6)‐dependent since OCLs from MVNP/IL‐6 −/− mice expressed lower levels of SphK‐1. Immunohistochemistry of bone biopsies from a normal donor, a PD patient, WT and MVNP mice confirmed increased expression levels of SphK‐1 in OCLs and S1PR3 in OBs of the PD patient and MVNP mice compared with normal donor and WT mice. Further, MVNP‐OCLs cocultured with OBs from MVNP or WT mice increased OB‐S1PR3 expression and enhanced expression of OB differentiation markers in MVNP‐OBs precursors compared with WT‐OBs, which was mediated by IL‐6 and insulin‐like growth factor 1 secreted by MVNP‐OCLs. Finally, the addition of an S1PR3 antagonist (VPC23019) to WT or MVNP‐OBs treated with WT and MVNP‐OCL‐conditioned media (CM) blocked enhanced OB differentiation of MVNP‐OBs treated with MVNP‐OCL‐CM. In contrast, the addition of the SIPR3 agonist, VPC24191, to the cultures enhanced osterix and Col‐1A expression in MVNP‐OBs treated with MVNP‐OCL‐CM compared with WT‐OBs treated with WT‐OCL‐CM. These results suggest that IL‐6 produced by PD‐OCLs increases S1P in OCLs and S1PR3 on OBs, to increase bone formation in PD., Model for the effects of sphingosine kinase‐1/sphingosine‐1‐phosphate/S1P‐receptor‐3 (SphK‐1/S1P/S1PR3) in abnormal bone remodeling in Paget's disease (PD). Measles virus nucleocapsid protein (MVNP) in PD‐osteoclasts (OCLs) induces interleukin‐6 (IL‐6), which upregulates insulin‐like growth factor 1 (IGF‐1) and Sphk1. SphK‐1 enhances S1P levels in OCLs, and IL‐6 and IGF‐1 increase S1PR3 on osteoblast (OBs). S1P then increases OB differentiation and bone formation via enhanced S1PR3 expression on OBs.

Shumin Rui, Takuo Kubota, Yasuhisa Ohata, Kenichi Yamamoto, Makoto Fujiwara, Shinji Takeyari, Keiichi Ozono, Phosphate promotes osteogenic differentiation through non-canonical Wnt signaling pathway in human mesenchymal stem cells, Bone, 2022, 164, 16525., Background: Phosphate is indispensable in osteogenesis and mineralization. However, mechanisms by which phosphate enhances osteogenic differentiation are not fully understood. In this study, we studied the effect of phosphate on osteogenic differentiation as well as signaling pathways induced by phosphate in the process. Method: Induced human bone marrow-derived mesenchymal stem cells differentiation into osteoblasts by the change of media containing β-glycerophosphate (GP), 1 mM inorganic phosphate, or 3 mM inorganic phosphate (Pi). The differentiation of osteoblasts was verified by the expression of osteoblast differentiation markers and calcium deposition. RNA sequencing was performed to assess transcriptome in the early stage of osteogenic differentiation. Results: Osteogenic differentiation and mineralization were promoted in the 3 mM Pi group compared to those in the GP and 1 mM Pi groups on day 7 of culture. RNA sequencing revealed that the gene expressions involved in osteogenesis and the components in the Wnt signaling pathway was increased in 3 mM Pi group compared with those in the GP on day 7. Analysis with qPCR and Western blot suggested upregulation of components in the non-canonical Wnt signaling pathway, including WNT5b and phosphorylated-c-Jun in the 3 mM Pi group on day 7. WNT11 mRNA expression was increased in the 2 induction groups on day 7. Inhibition of WNT5b by siRNA experiment attenuated the components in non-canonical Wnt signaling expression, including WNT5b, WNT11 and ROR2 mRNA expression and phosphorylated-c-Jun protein expression. In addition, osteogenic differentiation and mineralization were partly decreased in 3 mM Pi group on day 7 by the inhibition of WNT5b. Conclusion: Pi promoted osteogenic differentiation through the up-regulation of the non-canonical Wnt signaling pathway, including WNT5b, WNT11, p-c-Jun/c-Jun, in the early stage of differentiation. These findings provide a new perspective into the association of Pi and the non-canonical Wnt signaling pathway during osteogenic differentiation.

Hypophosphatasia (HPP; OMIM 241510, 241500, and 146300) is an inherited metabolic disease characterized by defects of bone and tooth mineralization, which is caused by loss-of-function mutations in the ALPL gene encoding tissue non-specific alkaline phosphatase (TNSALP). In the last three decades, several studies have focused on the genotype-phenotype correlation in hypophosphatasia (HPP). In particular, functional tests based on in vitro analysis for the residual enzymatic activities of mutations have revealed a clear but imperfect genotype-phenotype correlation, suggesting that multiple potential factors modulate the phenotype. One of the missense variants identified in the tissue non-specific alkaline phosphatase (ALPL) gene, c.787T>C, has been considered as a benign polymorphism in HPP; however, its pathogenicity and role in disease manifestation remain controversial. We here report our recent experience of three unrelated families harboring the c.787T>C variant, suggesting clinical implications regarding the controversial pathogenicity of c.787T>C. First, despite the lack of obvious clinical phenotypes, homozygous c.787T>C would decrease the serum level of ALP activity. Second, c.‍787T>C might deteriorate phenotypes of a patient harboring another ALPL variant, especially one that has thus far presumed to be benign, e.g., the c.1144G>A variant. These cases contribute to the recent advances in understanding HPP to facilitate clinical recognition of more subtle phenotypes, further providing insights into the pathogenesis of HPP.

Achondroplasia (ACH) is a skeletal dysplasia that presents with limb shortening, short stature, and characteristic facial configuration. ACH is caused by mutations of the FGFR3 gene, leading to constantly activated FGFR3 and activation of its downstream intracellular signaling pathway. This results in the suppression of chondrocyte differentiation and proliferation, which in turn impairs endochondral ossification and causes short-limb short stature. ACH also causes characteristic clinical symptoms, including foramen magnum narrowing, ventricular enlargement, sleep apnea, upper airway stenosis, otitis media, a narrow thorax, spinal canal stenosis, spinal kyphosis, and deformities of the lower extremities. Although outside Japan, papers on health supervision are available, they are based on reports and questionnaire survey results. Considering the scarcity of high levels of evidence and clinical guidelines for patients with ACH, clinical practical guidelines have been developed to assist both healthcare professionals and patients in making appropriate decisions in specific clinical situations. Eleven clinical questions were established and a systematic literature search was conducted using PubMed/MEDLINE. Evidence-based recommendations were developed, and the guidelines describe the recommendations related to the clinical management of ACH. We anticipate that these clinical practice guidelines for ACH will be useful for healthcare professionals and patients alike.

The oculocerebrorenal disorder of Lowe syndrome is an X-linked mutation in the gene oculocerebrorenal syndrome of Lowe 1 (OCRL), characterized by the triad of congenital cataracts, severe intellectual impairment, and renal tubular dysfunction. Manifestations of phenotype in female carriers and patients are extremely rare. We present a female case with congenital cataracts, severe intellectual impairment, sensorineural hearing loss, and renal tubular dysfunction as Lowe syndrome. A 9-year-old Japanese girl visited our hospital due to prolonged proteinuria. Her renal biopsy revealed diffuse mesangium proliferation, sclerosis and dilatation of renal tubules, and mild IgA deposition in the mesangial region. Furthermore, she had congenital cataracts, severe intellectual impairment, and sensorineural hearing loss. Genetic screening did not identify mutations of the ORCL gene encoding inositol polyphosphate 5-phosphatase (IPP-5P) (46 XX, female). However, we found the reduction of enzyme activity of IPP-5P to 50% of the normal value. Furthermore, her renal function had deteriorated to renal failure within a decade. Finally, she received peritoneal dialysis and renal transplantation. We present the oculocerebrorenal phenotype of Lowe syndrome in a female patient with reduced activity of IPP-5P without OCRL gene mutation.

HDR syndrome is characterized by the triad of primary hypoparathyroidism, sensorineural hearing loss and renal malformation with widely variable manifestations. It is an autosomal dominant inherited disease caused by a mutation of the GATA3 (NM_001002295.2), which is located on chromosome 10p14. Congenital heart disease, such as tetralogy of Fallot, a typical complication of DiGeorge syndrome, is a rare complication of HDR syndrome. We herein report a case of HDR syndrome coexisting tetralogy of Fallot with a novel mutation, c.964C > T (p.Gln322*). This case suggested that the screening of renal involvement should be carefully performed in patients with a phenotypic combination of hypoparathyroidism and sensorineural hearing loss, to facilitate the early diagnosis of HDR syndrome. In addition, when the deletion of chromosome 22q11.2 is not detected by a fluorescence in situ hybridization analysis in patients exhibiting the partial phenotype of DiGeorge syndrome, the possibility of HDR syndrome should be considered and the renal function should be repeatedly evaluated.

Hypophosphatasia (HPP; OMIM 241510, 241500, and 146300) is an inherited metabolic disease characterized by defects of bone and tooth mineralization, which is caused by loss-of-function mutations in the ALPL gene encoding tissue non-specific alkaline phosphatase (TNSALP). In the last three decades, several studies have focused on the genotype-phenotype correlation in hypophosphatasia (HPP). In particular, functional tests based on in vitro analysis for the residual enzymatic activities of mutations have revealed a clear but imperfect genotype-phenotype correlation, suggesting that multiple potential factors modulate the phenotype. One of the missense variants identified in the tissue non-specific alkaline phosphatase (ALPL) gene, c.787TC, has been considered as a benign polymorphism in HPP; however, its pathogenicity and role in disease manifestation remain controversial. We here report our recent experience of three unrelated families harboring the c.787TC variant, suggesting clinical implications regarding the controversial pathogenicity of c.787TC. First, despite the lack of obvious clinical phenotypes, homozygous c.787TC would decrease the serum level of ALP activity. Second, c.787TC might deteriorate phenotypes of a patient harboring another ALPL variant, especially one that has thus far presumed to be benign, e.g., the c.1144GA variant. These cases contribute to the recent advances in understanding HPP to facilitate clinical recognition of more subtle phenotypes, further providing insights into the pathogenesis of HPP.

Congenital generalized lipodystrophy type 4 (CGL4) is a rare disease caused by mutations in the gene polymerase I and transcript release factor (PTRF), the main symptoms of which are systemic reductions in adipose tissue and muscular dystrophy. The strategy of treating CGL4 is to improve the insulin resistance and hypertriglyceridemia that result from systemic reductions in adipose tissue. Metreleptin, a synthetic analog of human leptin, is effective against generalized lipodystrophies; however, there are no reports of the use of metreleptin in the treatment of CGL4. Herein, we discuss the treatment of a six-year-old boy diagnosed with CGL4 due to a homozygous mutation in PTRF with metreleptin. His serum triglyceride level and homeostasis model assessment of insulin resistance (HOMA-IR) value decreased after two months of metreleptin treatment. However, the efficacy of metreleptin gradually decreased, and the treatment was suspended because anaphylaxis occurred after the dosage administered was increased. Subsequently, his serum triglyceride level and HOMA-IR value significantly increased. Anti-metreleptin-neutralizing antibodies were detected in his serum, which suggested that these antibodies reduced the efficacy of metreleptin and caused increased hypersensitivity. Thus, metreleptin appeared to be efficacious in the treatment of CGL4 in the short term, although an adverse immune response resulted in treatment suspension. Further studies are needed to evaluate metreleptin treatments for CGL4.

X-linked hypophosphatemia (XLH) is the most common form of heritable hypophosphatemic rickets. We encountered a 4-year-old boy with a novel variant in the phosphate-regulating neutral endopeptidase homolog X-linked (PHEX) gene who presented with a short stature, genu valgum, and scaphocephaly. The same mutation was identified in his mother and sister; however, the patient presented with a more severe case.

X-linked hypophosphatemic rickets (XLH) is an inheritable type of rickets caused by inactivating variants in the phosphate regulating endopeptidase homolog X-linked (PHEX) gene, which results in the overproduction of fibroblast growth factor 23 (FGF23). The mechanism by which PHEX impairment leads to FGF23 overproduction is unknown. Because little is known regarding the genotype-phenotype correlation in Japanese XLH, we summarized the available clinical and genetic data and analyzed the genotype-phenotype relationships using 3-dimensional (3D) structure modeling to clarify the XLH pathophysiology. We retrospectively reviewed the clinical features and performed genetic analysis of 39 Japanese patients with XLH from 28 unrelated pedigrees carrying any known or novel PHEX variant. To predict changes in the 3D structure of mutant PHEX, we constructed a putative 3D model of each mutant and evaluated the effect of structural alteration by genotype-phenotype correlation analysis. Genetic analysis revealed 23 PHEX variants, including eight novel variants. They were associated with high i-FGF23 levels, hypophosphatemia, phosphaturia, high alkaline phosphatase levels, and short stature. No gene dosage effect or genotype-phenotype correlation was observed when truncating and non-truncating variants were compared. However, the conservation of the zinc-binding site and cavity in PHEX had an impact on the elevation of i-FGF23 levels. Via genotype-phenotype relationship analysis using 3D modeling, we showed that the zinc-binding site and cavity in PHEX can play a critical role in its function. These findings provide new genetic clues for investigating the function of PHEX and the pathogenesis of XLH.

A 40-year-old Japanese woman presented to our hospital with general fatigue and muscle weakness. She had a history of premature loss of deciduous teeth at 4 years old, her serum alkaline phosphatase (ALP) activity was as low as 91 U/L, and radiologic studies revealed thoracic deformity and sacroiliac calcification. Genetic sequencing revealed a heterozygous c.1559delT mutation in the tissue non-specific alkaline phosphatase gene (ALPL). Based on these findings, she was diagnosed with hypophosphatasia (HPP), and treatment with asfotase alfa, a recombinant human tissue-nonspecific alkaline phosphatase (TNSALP), was initiated. After six months of treatment with asfotase alfa, improvements were observed in the SF-36 score, six-minute walk distance, and grasping power. Although the overdiagnosis needs to be avoided, HPP should be considered in patients with undiagnosed musculoskeletal symptoms and a low serum ALP activity.

We report that transgenic mice expressing measles virus nucleocapsid protein (MVNP) in osteoclasts (OCLs) (MVNP mice) are Paget's disease (PD) models and that OCLs from patients with PD and MVNP mice express high levels of OCL-derived IGF1 (OCL-IGF1). To determine OCL-IGF1's role in PD and normal bone remodeling, we generated WT and MVNP mice with targeted deletion of Igf1 in OCLs (Igf1-cKO) and MVNP/Igf1-cKO mice, and we assessed OCL-IGF1's effects on bone mass, bone formation rate, EphB2/EphB4 expression on OCLs and osteoblasts (OBs), and pagetic bone lesions (PDLs). A total of 40% of MVNP mice, but no MVNP/Igf1-cKO mice, had PDLs. Bone volume/tissue volume (BV/TV) was decreased by 60% in lumbar vertebrae and femurs of MVNP/Igf1-cKO versus MVNP mice with PDLs and by 45% versus all MVNP mice tested. Bone formation rates were decreased 50% in Igf1-cKO and MVNP/Igf1-cKO mice versus WT and MVNP mice. MVNP mice had increased EphB2 and EphB4 levels in OCLs/OBs versus WT and MVNP/Igf1-cKO, with none detectable in OCLs/OBs of Igf1-cKO mice. Mechanistically, IL-6 induced the increased OCL-IGF1 in MVNP mice. These results suggest that high OCL-IGF1 levels increase bone formation and PDLs in PD by enhancing EphB2/EphB4 expression in vivo and suggest OCL-IGF1 may contribute to normal bone remodeling.

Objective IGF2 is a paternally expressed growth-promoting gene. Here, we report five cases with IGF2 mutations and review IGF2 mutation-positive patients described in the literature. We also compare clinical features between patients with IGF2 mutations and those with H19/IGF2:IG-DMR epimutations. Results We recruited five cases with IGF2 mutations: case 1 with a splice site mutation (c.–6–1G>C) leading to skipping of exon 2 and cases 2–5 with different missense mutations (p.(Cys70Tyr), p.(Cys71Arg), p.(Cys33Ser), and p.(Cys45Ser)) affecting cysteine residues involved in the S-S bindings. All the mutations resided on the paternally inherited allele, and the mutation of case 5 was present in a mosaic condition. Clinical assessment revealed Silver–Russell syndrome (SRS) phenotype with Netchine–Harbison scores of ≥5/6 in all the apparently nonmosaic 14 patients with IGF2 mutations (cases 1–4 described in this study and 10 patients reported in the literature). Furthermore, compared with H19/IGF2:IG-DMR epimutations, IGF2 mutations were associated with low frequency of hemihypoplasia, high frequency of feeding difficulty and/or reduced body mass index, and mild degree of relative macrocephaly, together with occasional development of severe limb malformations, high frequency of cardiovascular anomalies and developmental delay, and low serum IGF-II values. Conclusions This study indicates that IGF2 mutations constitute a rare but important cause of SRS. Furthermore, while both IGF2 mutations and H19/IGF2:IG-DMR epimutations lead to SRS, a certain degree of phenotypic difference is observed between the two groups, probably due to the different IGF2 expression pattern in target tissues.

Basal cell nevus syndrome (BCNS) is a rare, multisystem, autosomal dominant disorder that is characterized by various phenotypes, including multiple basal cell carcinomas of the skin, odontogenic keratocysts of the jaws, and occasionally cleft lip and/or palate. In this report, we describe a 6-year-old Japanese girl with a novel heterozygous nonsense mutation in PTCH1 who exhibited rare craniofacial phenotypes, such as oligodontia and a short-tooth root.

Paget’s disease (PD) is characterized by focal and dramatic bone resorption and formation. Treatments that target osteoclasts (OCLs) block both pagetic bone resorption and formation; therefore, PD offers key insights into mechanisms that couple bone resorption and formation. Here, we evaluated OCLs from 3 patients with PD and determined that measles virus nucleocapsid protein (MVNP) was expressed in 70% of these OCLs. Moreover, transgenic mice with OCL-specific expression of MVNP (MVNP mice) developed PD-like bone lesions that required MVNP-dependent induction of high IL-6 expression levels in OCLs. In contrast, mice harboring a knockin of p62P394L (p62-KI mice), which is the most frequent PD-associated mutation, exhibited increased bone resorption, but not formation. Evaluation of OCLs from MVNP, p62-KI, and WT mice revealed increased IGF1 expression in MVNP-expressing OCLs that resulted from the high IL-6 expression levels in these cells. IL-6, in turn, increased the expression of coupling factors, specifically ephrinB2 on OCLs and EphB4 on osteoblasts (OBs). IGF1 enhanced ephrinB2 expression on OCLs and OB differentiation. Importantly, ephrinB2 and IGF1 levels were increased in MVNP-expressing OCLs from patients with PD and MVNP-transduced human OCLs compared with levels detected in controls. Further, anti-IGF1 or anti-IGF1R blocked Runx2 and osteocalcin upregulation in OBs cocultured with MVNP-expressing OCLs. These results suggest that in PD, MVNP upregulates IL-6 and IGF1 in OCLs to increase ephrinB2-EphB4 coupling and bone formation.

Osteogenesis imperfecta (OI) is a heritable brittle bone disease mainly caused by mutations in the two type I collagen genes. Collagen synthesis is a complex process including trimer formation, glycosylation, secretion, extracellular matrix (ECM) formation, and mineralization. Using OI patient-derived fibroblasts and induced pluripotent stem cells (iPSCs), we investigated the effect of 4-phenylbutyric acid (4-PBA) on collagen synthesis to test its potential as a new treatment for OI. Endoplasmic reticulum (ER) retention of type I collagen was observed by immunofluorescence staining in OI patient-derived fibroblasts with glycine substitution and exon skipping mutations. Liquid chromatography–mass spectrometry analysis revealed excessive glycosylation of secreted type I collagen at the specific sites in OI cells. The misfolding of the type I collagen triple helix in the ECM was demonstrated by the incorporation of heat-dissociated collagen hybridizing peptide in OI cells. Type I collagen was produced excessively by OI fibroblasts with a glycine mutation, but this excessive production was normalized when OI fibroblasts were cultured on control fibroblast-derived ECM. We also found that mineralization was impaired in osteoblasts differentiated from OI iPSCs. In summary, treatment with 4-PBA normalizes the excessive production of type I collagen, reduces ER retention, partially improves misfolding of the type I collagen helix in ECM, and improves osteoblast mineralization. Thus, 4-PBA may improve not only ER retention, but also type I collagen synthesis and mineralization in human cells from OI patients.

Basal cell nevus syndrome (BCNS) is a rare, multisystem, autosomal dominant disorder that is characterized by various phenotypes, including multiple basal cell carcinomas of the skin, odontogenic keratocysts of the jaws, and occasionally cleft lip and/or palate. In this report, we describe a 6-year-old Japanese girl with a novel heterozygous nonsense mutation in PTCH1 who exhibited rare craniofacial phenotypes, such as oligodontia and a short-tooth root.

Acrodysostosis is characterized by distinctive facial features and severe brachydactyly. Mutations in PRKAR1A or PDE4D are known to be responsible for this disease. Cases of hormonal resistance have been reported, particularly in patients with PRKAR1A mutations. The physical characteristics and endocrine function of pseudohypoparathyroidism type Ia is known to resemble acrodysostosis. We report the case of a 4-yr-old patient with a PRKAR1A mutation. He had characteristic facies with an upturned nose and cone-shaped epiphyses of most phalanges. These findings have not been reported as extensive for cases of pseudohypoparathyroidism type Ia. He also had TSH resistance from birth. We performed endocrinological stimulation tests to further evaluate his endocrine status. These examinations revealed resistance to TSH and PTH, but there was normal secretion of ACTH, GH, and cortisol. An Ellsworth-Howard test resulted in normal urinary cAMP excretion. This response differs from that of pseudohypoparathyroidism type Ia. In summary, the constellation of an upturned nose, cone-shaped epiphyses of most if not all phalanges, and PTH resistance with a normal urinary cAMP response may satisfactorily enable clinical diagnosis of acrodysostosis.

The serum levels of calcium (Ca) and phosphate are maintained higher in the fetus than in the pregnant mother, especially in late gestation, to meet the demands of fetal bone development. In order to maintain this fetal stage-specific mineral homeostasis, the placenta plays a critical role through active transcellular mineral transport. Although the molecular mechanism of transplacental Ca transport has been well studied, little is known about the transport mechanism of phosphate and magnesium. Maternal mineral homeostasis is also altered during pregnancy to supply minerals to the fetus. In the lactating mother, osteocytic osteolysis is suggested to be involved in the supply of minerals to the baby. The levels of some calcitropic and phosphotropic (Ca- and phosphate-regulating, respectively) hormones in the fetus are also different from those in the adult. The PTH level in the fetus is lower than that in the mother and nonpregnant adult. It is suggested, however, that low fetal PTH plays an important role in fetal mineral metabolism. The concentration of PTHrP in the fetus is much higher than that of PTH and plays a critical role in perinatal Ca homeostasis. Uncovering the molecular mechanisms for fetal stage-specific mineral metabolism will lead to better management of perinatal patients with mineral abnormalities.

Pneumocystis jiroveci pneumonia (PCP) is a serious complication in patients receiving chemotherapy or hematopoietic stem cell transplantation. Current recommendations for trimethoprim-sulfamethoxazole (TMP-SMZ) dosing as PCP prophylaxis in immunocompromised patients are based on either daily dosing or dosing three consecutive days per week. We report our experience of prophylaxis with TMP-SMZ twice daily on two non-consecutive days per week in 145 immunocompromised children with hematologic disorders, cancer, or metabolic disorders following chemotherapy or hematopoietic stem cell transplantation. There were no breakthrough cases of PCP. We therefore conclude our prophylaxis regimen is effective against PCP in immunocompromised children.

Fibroblast growth factor 23 (FGF23) functions in an endocrine fashion and requires α-Klotho to exert its effects on the target organs. We have recently demonstrated that the human placenta also expresses α-Klotho, which led us to hypothesize that FGF23 may exert effects on the placenta. Immunohistochemical analysis demonstrated the expression of FGF receptor 1 (FGFR1) as well as that of α-Klotho in the feto-maternal interface of both mouse and human normal-term placentas, which suggested that these areas might be receptive to FGF23. Therefore, we next investigated whether FGF23 has some roles in the placenta using Hyp mice with high levels of circulating FGF23. Hyp and wild-type (WT) females were mated with WT males, and the mothers and their male fetuses were analyzed. FGF23 levels in Hyp mothers were elevated. FGF23 levels were about 20-fold higher in Hyp fetuses than in Hyp mothers, whereas WT fetuses from Hyp mothers exhibited low levels of FGF23, as did fetuses from WT mothers. We analyzed the placental gene expression and found that the expression of Cyp24a1 encoding 25OHD-24-hydroxylase, a target gene for FGF23 in the kidney, was increased in the placentas of fetuses from Hyp mothers compared with fetuses from WT mothers. In an organ culture of WT placentas, treatment with plasma from Hyp mothers markedly increased the expression of Cyp24a1, which was abolished by the simultaneous addition of anti-FGF23 neutralizing antibody. The direct injection of recombinant FGF23 into WT placentas induced the expression of Cyp24a1. The increase in the placental expression of Cyp24a1 in fetuses from Hyp mothers resulted in decreased plasma 25-hydroxyvitamin D levels. These results suggest that increased levels of circulating FGF23 in pathological conditions such as Hyp mice exerts direct effects on the placenta and affects fetal vitamin D metabolism via the regulation of Cyp24a1 expression.

1,25 dihydroxy vitamin D3 (1,25D) plays multiple roles in normal and malignant cell functions, including cell differentiation and proliferation, and is a regulator of bone metastasis. However, the role of 1,25D in multiple myeloma (MM) is poorly characterized. We previously showed that TAF12, a member of the TFIID transcription complex, acts as a co-activator for vitamin D receptor (VDR) mediated transcription to increase 1,25D responsivity. Further, we reported that IL-6 can increase TAF12 levels in bone marrow stromal cells (BMSC). Since IL-6 is upregulated in the MM microenvironment, we assessed TAF12 levels in BMSC from 13 MM patients and 10 normals. TAF12 protein levels were significantly increased (25x) in MM BMSC compared to normal. Further, co-culture of BMSC from 3 normals with primary human MM cells significantly increased TAF12 levels in the normal BMSC. Similarly, when 5TGM-1 murine MM cells were inoculated intratibially into C57BL/KaLwRij mice and bone marrow cells collected 3 weeks later, TAF12 protein levels in MM exposed BMSC were significantly increased compared to PBS injected control mice. We then assessed if increased TAF12 levels persisted in normal BMSC (SAKA-T cells) after they were co-cultured with JJN3 MM cells and subsequently cultured in the absence of MM cells. We found that increased TAF12 levels persisted for at least 2 weeks after removal of MM cells, consistent with our findings that BMSC from MM patients express elevated TAF12 levels in the absence of MM cells. To determine if IL-6 contributes to the increased TAF12 levels induced by MM cells, we co-cultured SAKA-T cells with JJN3 MM cells in the presence or absence of anti-IL-6. Anti-IL-6 blocked the increase in TAF12 levels in these co-cultures. We then tested if the increased TAF12 levels enhance the 1,25D responsivity of BMSC. Addition of 1,25D (10-10 - 10-8 M) greatly increased expression of RANKL mRNA and VCAM-1 protein in MM BMSC compared to normals. The increased RANKL and VCAM-1 in MM BMSC treated with 1,25D correlated with increased osteoclast (OCL) formation, MM cell growth and adhesion of MM cells. When human OCL precursors and MM or normal BMSC were co-cultured with 1,25D with/without osteoprotegerin (OPG), OCL numbers were significantly increased in co-cultures of MM BMSC treated with 1,25D compared to normal, and the increase was blocked by OPG. Further, co-culture of JJN3 cells with normal or MM BMSC and 1,25D for 6 hours followed by removal of non-adherent MM cells, demonstrated that the number of MM cells adherent to BMSC was significantly increased with 1,25D treatment of MM BMSC co-cultures compared to normal BMSC. In addition, when JJN3 cells were co-cultured with normal or MM BMSC and 1,25D, JJN3 cells numbers were significantly increased in co-cultures with MM BMSC compared to normal BMSC. Finally, we determined if high levels of TAF12 in MM BMSC increased their 1,25D responsivity. We knocked-down (k/d) TAF12 with a siRNA in normal and MM BMSC, and found that TAF12 k/d in MM or normal BMSC decreased the levels of VCAM 1 induced by 1,25D compared to control siRNA transduced cells. To further investigate this effect, we assessed if TAF12 levels affected the stability of VDR in the presence of 1,25D, using TAF12 heterozygous or WT mouse BMSC. VDR half-life was decreased approximately 50% in TAF12 heterozygous BMSC compared with WT. These results show that MM cells increase expression of TAF12 in BMSC that is mediated by IL-6. BMSCs expressing high TAF12 levels have greater responsivity to 1,25D that enhances RANKL and VCAM-1 expression to induce osteoclastogenesis, MM cell growth and MM cell adhesion. These results further suggest that blocking TAF12 -VDR interactions may be a potential therapeutic target for MM bone disease. Disclosures Roodman: Amgen: Consultancy.

Fibroblast growth factor-23 (FGF23) is well established to play crucial roles in the regulation of phosphate homeostasis. X-linked hypophosphatemic rickets (XLH) is characterized by impaired mineralization and growth retardation associated with elevated circulating FGF23 levels. Administration of phosphate and calcitriol is effective in improving growth retardation, but is not sufficient to fully reverse impaired growth, suggesting the existence of a disease-specific mechanism in the development of growth retardation in addition to dysregulated phosphate metabolism. However, the precise mechanisms of growth retardation in XLH remain elusive. Here, we postulated that FGF23 suppressed chondrocyte proliferation in the presence of soluble α-Klotho (sKL). In vitro and ex vivo studies revealed that FGF23 formed a protein complex with sKL through KL1 internal repeat and suppressed the linear growth of metatarsals in the presence of sKL, which was antagonized by co-incubation with neutralizing antibodies against FGF23 or by knocking-down FGFR3 expression. Additionally, FGF23 binding to FGFR3 was enhanced in the presence of sKL. Histologically, the length of the proliferating zone was diminished and was associated with decreased chondrocyte proliferation. FGF23/sKL suppressed Indian hedgehog (Ihh) expression and administration of Ihh protein partially rescued the suppressive effect of FGF23/sKL on metatarsal growth. Intraperitoneal administration of sKL in Hyp mice, a murine model for XLH, caused a decrease in the length of the proliferating zone associated with decreased chondrocyte proliferation without altering circulating phosphate levels. These findings suggest that suppression of chondrocyte proliferation by FGF23 could have a causative role in the development of growth retardation in XLH. Background: The role of elevated FGF23 in the development of growth retardation associated with X-linked hypophosphatemic rickets (XLH) remains elusive. Results: FGF23 suppresses chondrocyte proliferation in cooperation with soluble α-Klotho. Conclusion: Elevated FGF23 could have a causative role in the development of growth retardation in XLH. Significance: This may provide insights into the unrecognized function of FGF23 signaling in chondrocyte biology.

A 10-yr-old boy visited Minoh City Hospital complaining of gross hematuria. Laboratory investigations revealed hypercalcemia, hypophosphatemia, and elevated serum levels of parathyroid hormone. A stone was found in the right ureter with drip infusion pyelography. A parathyroid adenoma was successfully diagnosed with computed tomography, ultrasonography, and methoxy-2-isobutyl isonitrile (MIBI) scintigraphy. Multiple endocrine neoplasia was ruled out by normal results of endocrine laboratory examinations. Extracorporeal shock wave lithotripsy was performed to treat the urolithiasis, and the parathyroid adenoma was surgically removed. Primary hyperparathyroidism is rare in childhood; however, this case suggests that gross hematuria is an important sign of hyperparathyroidism.

Osteocytes express multiple genes involved in mineral metabolism including PHEX, FGF23, DMP1 and FAM20C. In Hyp mice, a murine model for X-linked hypophosphatemia (XLH), Phex deficiency results in the overproduction of FGF23 in osteocytes, which leads to hypophosphatemia and impaired vitamin D metabolism. In this study, to further clarify the abnormality in osteocytes of Hyp mice, we obtained detailed gene expression profiles in osteoblasts and osteocytes isolated from the long bones of 20-week-old Hyp mice and wild-type (WT) control mice. The expression of Fgf23, Dmp1, and Fam20c was higher in osteocytic cells than in osteoblastic cells in both genotypes, and was up-regulated in Hyp cells. Interestingly, the up-regulation of these genes in Hyp bones began before birth. On the other hand, the expression of Slc20a1 encoding the sodium/phosphate (Na+/Pi) co-transporter Pit1 was increased in osteoblasts and osteocytes from adult Hyp mice, but not in Hyp fetal bones. The direct effects of extracellular Pi and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on isolated osteoblastic and osteocytic cells were also investigated. Twenty-four-hour treatment with 10-8 M 1,25(OH)2D3 increased the expression of Fgf23 in WT osteoblastic cells but not in osteocytic cells. Dmp1 expression in osteocytic cells was increased due to the 24-hour treatment with 10 mM Pi and was suppressed by 10-8 M 1,25(OH)2D3 in WT osteocytic cells. We also found the up-regulation of the genes for FGF1, FGF2, their receptors, and Egr-1 which is a target of FGF signaling, in Hyp osteocytic cells, suggesting the activation of FGF/FGFR signaling. These results implicate the complex gene dysregulation in osteoblasts and osteocytes of Hyp mice, which might contribute to the pathogenesis.

We describe a three-generation family with tall stature, scoliosis and macrodactyly of the great toes and a heterozygous p.Val883Met mutation in Npr2, the gene that encodes the CNP receptor NPR2 (natriuretic peptide receptor 2). When expressed in HEK293A cells, the mutant Npr2 cDNA generated intracellular cGMP (cyclic guanosine monophosphate) in the absence of CNP ligand. In the presence of CNP, cGMP production was greater in cells that had been transfected with the mutant Npr2 cDNA compared to wild-type cDNA. Transgenic mice in which the mutant Npr2 was expressed in chondrocytes driven by the promoter and intronic enhancer of the Col11a2 gene exhibited an enhanced production of cGMP in cartilage, leading to a similar phenotype to that observed in the patients. In addition, blood cGMP concentrations were elevated in the patients. These results indicate that p.Val883Met is a constitutive active gain-of-function mutation and elevated levels of cGMP in growth plates lead to the elongation of long bones. Our findings reveal a critical role for NPR2 in skeletal growth in both humans and mice, and may provide a potential target for prevention and treatment of diseases caused by impaired production of cGMP.