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The C1QBP protein (complement component 1 Q subcomponent‐binding protein), encoded by the C1QBP gene, is a multifunctional protein predominantly localized in the mitochondrial matrix. Biallelic variants have previously been shown to give rise to combined respiratory‐chain deficiencies with variable phenotypic presentation, severity, and age at onset, from intrauterine with a mostly lethal course, to a late‐onset mild myopathy. We present two fetuses, one male and one female, of first‐cousin parents, with severe intrauterine growth retardation, oligo/anhydramnios, edema, and cardiomyopathy as the most prominent prenatal symptoms. Both fetuses showed no copy number variants by chromosome microarray analysis. Analysis of a fibroblast culture from one of the fetuses showed deficiency of respiratory chain complex IV, and using exome sequencing, we identified homozygosity for a novel variant in C1QBP in both fetuses. To our knowledge, only six patients with pathogenic variants in C1QBP have been reported previously and with this report, we add a novel pathogenic variant in C1QBP found in two related fetuses.

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.

Objective To study the impact of gender, puberty, and pregnancy on the expression of POLG disease, one of the most common mitochondrial diseases known. Methods Clinical, laboratory, and genetic data were collected retrospectively from 155 patients with genetically confirmed POLG disease recruited from seven European countries. We used the available data to study the impact of gender, puberty, and pregnancy on disease onset and deterioration. Results We found that disease onset early in life was common in both sexes but there was also a second peak in females around the time of puberty. Further, pregnancy had a negative impact with 10 of 14 women (71%) experiencing disease onset or deterioration during pregnancy. Interpretation Gender clearly influences the expression of POLG disease. While onset very early in life was common in both males and females, puberty in females appeared associated both with disease onset and increased disease activity. Further, both disease onset and deterioration, including seizure aggravation and status epilepticus, appeared to be associated with pregnancy. Thus, whereas disease activity appears maximal early in life with no subsequent peaks in males, both menarche and pregnancy appear associated with disease onset or worsening in females. This suggests that hormonal changes may be a modulating factor. © 2020 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Mitochondrial disorders are one of the most common inherited metabolic disorders and are caused by variants in nuclear genes or the mitochondrial genome. Additionally, there is a large group of patients displaying clinical symptoms, where the genetic background is unknown. Mitochondrial disorders have a huge variety in their clinical presentation, making diagnostics challenging. Genomes of higher organisms contain around 95% non-protein-coding DNA. Recently, non-protein-coding sequences have been shown to affect gene expression in many cellular processes, including mitochondrial functioning. As these insights are not frequently incorporated in diagnostics we propose a workflow utilizing this knowledge for faster diagnostics of patients lacking a molecular diagnosis.

Background Reversible infantile respiratory chain deficiency (RIRCD) is a rare mitochondrial disorder associated with variable penetrance and partial to full remission of symptoms. Objective To describe features of maternally related individuals with a novel variant associated with RIRCD. Materials and methods Nine maternally related individuals aged 23 months to 64 years are described through physical examinations, muscle biopsies, histochemical and biochemical analyses, genome sequencing, and cerebral imaging. Results A homoplasmic mitochondrial transfer ribonucleic acid for glutamic acid (mt-tRNAGlu) m.14701C>T variant was identified in eight tested individuals out of nine maternally related individuals. Two individuals presented with hypotonia, muscle weakness, feeding difficulties and lactic acidosis at age 3–4 months, and improvement around age 15–23 months with mild residual symptoms at last examination. One individual with less severe symptoms had unknown age at onset and improved around age 4–5 years. Five individuals developed lipoma on the upper back, and one adult individual developed ataxia, while one was unaffected. Conclusions We have identified a novel homoplasmic mt-tRNAGlu m.14701C>T variant presenting with phenotypic and paraclinical features associated with RIRCD as well as ataxia and lipomas, which to our knowledge are new features associated to RIRCD.

Background Variants in POLG are one of the most common causes of inherited mitochondrial disease. Phenotypic classification of POLG disease has evolved haphazardly making it complicated and difficult to implement in everyday clinical practise. The aim of our study was to simplify the classification and facilitate better clinical recognition. Methods A multinational, retrospective study using data from 155 patients with POLG variants recruited from seven European countries. Results We describe the spectrum of clinical features associated with POLG variants in the largest known cohort of patients. While clinical features clearly form a continuum, stratifying patients simply according to age of onset—onset prior to age 12 years; onset between 12 and 40 years and onset after the age of 40 years, permitted us to identify clear phenotypic and prognostic differences. Prior to 12 years of age, liver involvement (87%), seizures (84%), and feeding difficulties (84%) were the major features. For those with onset between 12 and 40 years, ataxia (90%), peripheral neuropathy (84%), and seizures (71%) predominated, while for those with onset over 40 years, ptosis (95%), progressive external ophthalmoplegia (89%), and ataxia (58%) were the major clinical features. The earlier the onset the worse the prognosis. Patients with epilepsy and those with compound heterozygous variants carried significantly worse prognosis. Conclusion Based on our data, we propose a simplified POLG disease classification, which can be used to guide diagnostic investigations and predict disease course. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Mitochondrial acyl-coenzyme A species are emerging as important sources of protein modification and damage. Succinyl-CoA ligase (SCL) deficiency causes a mitochondrial encephalomyopathy of unknown pathomechanism. Here, we show that succinyl-CoA accumulates in cells derived from patients with recessive mutations in the tricarboxylic acid cycle (TCA) gene succinyl-CoA ligase subunit-β (SUCLA2), causing global protein hyper-succinylation. Using mass spectrometry, we quantify nearly 1,000 protein succinylation sites on 366 proteins from patient-derived fibroblasts and myotubes. Interestingly, hyper-succinylated proteins are distributed across cellular compartments, and many are known targets of the (NAD+)-dependent desuccinylase SIRT5. To test the contribution of hyper-succinylation to disease progression, we develop a zebrafish model of the SCL deficiency and find that SIRT5 gain-of-function reduces global protein succinylation and improves survival. Thus, increased succinyl-CoA levels contribute to the pathology of SCL deficiency through post-translational modifications., The pathomechanism of succinyl-CoA ligase (SCL) deficiency, a hereditary mitochondrial disease, is not fully understood. Here, the authors show that increased succinyl-CoA levels contribute to SCL pathology by causing global protein hyper-succinylation.

An intact and dynamic microtubule cytoskeleton is crucial for the development, differentiation, and maintenance of the mammalian cortex. Variants in a host of structural microtubulin-associated proteins have been identified to cause a wide spectrum of malformations of cortical development and alterations of microtubule dynamics have been recognized to cause or contribute to progressive neurodegenerative disorders. TBCD is one of the five tubulin-specific chaperones and is required for reversible assembly of the α-/β-tubulin heterodimer. Recently, variants in TBCD, and one other tubulin-specific chaperone, TBCE, have been identified in patients with distinct progressive encephalopathy with a seemingly broad clinical spectrum. Here, we report the clinical, neuroradiological, and neuropathological features in eight patients originating from the Faroe Islands, who presented with an early onset, progressive encephalopathy with features of primary neurodegeneration, and a homogenous clinical course. These patients were homozygous for a TBCD missense variant c.[3099C>G]; p.(Asn1033Lys), which we show has a high carrier frequency in the Faroese population (2.6%). The patients had similar age of onset as the previously reported patients (n = 24), but much shorter survival, which could be caused by either differences in supportive treatment, or alternatively, that shorter survival is intrinsic to the Faroese phenotype. We present a detailed description of the neuropathology and MR imaging characteristics of a subset of these patients, adding insight into the phenotype of TBCD-related encephalopathy. The finding of a Faroese founder variant will allow targeted genetic diagnostics in patients of Faroese descent as well as improved genetic counseling and testing of at-risk couples.

In most patients with intellectual disability (ID), the etiology is unknown, but lately several de novo variants have been associated with ID. One of the involved genes, CUX2, has twice been reported to be affected by a de novo variant c.1768G>A; p.(Glu590Lys) in patients with ID or epileptic encephalopathy. CUX2 is expressed primarily in nervous tissues where it may act as a transcription factor involved in neural specification. Here we describe a third case who was diagnosed with epilepsy including general and myoclonic seizures, moderate to severe cognitive disability, and infantile autism. The patient was heterozygous for the c.1768G>A; p.(Glu590Lys) variant in CUX2 identified by whole exome sequencing. These findings strongly suggest a causal impact of this variant and add to our understanding of a subset of patients with ID, seizures, and autism spectrum disorder as well as suggest an important role for the CUX2 gene in human brain function.

BackgroundLeigh syndrome is a phenotypically and genetically heterogeneous mitochondrial disorder. While some genetic defects are associated with well-described phenotypes, phenotype-genotype correlations in Leigh syndrome are not fully explored.ObjectiveWe aimed to identify phenotype-genotype correlations in Leigh syndrome in a large cohort of systematically evaluated patients.MethodsWe studied 96 patients with genetically confirmed Leigh syndrome diagnosed and followed in eight European centres specialising in mitochondrial diseases.ResultsWe found that ataxia, ophthalmoplegia and cardiomyopathy were more prevalent among patients with mitochondrial DNA defects. Patients with mutations in MT-ND and NDUF genes with complex I deficiency shared common phenotypic features, such as early development of central nervous system disease, followed by high occurrence of cardiac and ocular manifestations. The cerebral cortex was affected in patients with NDUF mutations significantly more often than the rest of the cohort. Patients with the m.8993T>G mutation in MT-ATP6 gene had more severe clinical and radiological manifestations and poorer disease outcome compared with patients with the m.8993T>C mutation.ConclusionOur study provides new insights into phenotype-genotype correlations in Leigh syndrome and particularly in patients with complex I deficiency and with defects in the mitochondrial ATP synthase.

The hypomyelinating leukodystrophies (HMLs) encompass the X-linked Pelizaeus-Merzbacher disease (PMD) caused by PLP1 mutations and known as the classical form of HML as well as Pelizaeus-Merzbacher-like disease (PMLD) (Online Mendelian Inheritance in Man [OMIM] 608804 and OMIM 260600) due to GJC2 mutations. In addition, mutations in at least 10 other genes are known to cause HMLs. In 2008, an Israeli family with clinical and neuroimaging findings similar to those found in PMD was reported. The patients were found to have a homozygous missense mutation in HSPD1, encoding the mitochondrial heat-shock protein 60 (Hsp60), and the disorder was defined as the autosomal recessive mitochondrial Hsp60 chaperonopathy (MitCHAP-60) disease. We here report the first case of this severe neurodegenerative disease since it was first described. Given the fact that the families carried the same mutation our patient probably belongs to the same extended family as the Israeli family. In conclusion, the MitCHAP-60 disease should be considered as a rare differential diagnosis in HML.

Autosomal-recessive albinism is a hypopigmentation disorder with a broad phenotypic range. A substantial fraction of individuals with albinism remain genetically unresolved, and it has been hypothesized that more genes are to be identified. By using homozygosity mapping of an inbred Faroese family, we identified a 3.5 Mb homozygous region (10q22.2–q22.3) on chromosome 10. The region contains five protein-coding genes, and sequencing of one of these, C10orf11, revealed a nonsense mutation that segregated with the disease and showed a recessive inheritance pattern. Investigation of additional albinism-affected individuals from the Faroe Islands revealed that five out of eight unrelated affected persons had the nonsense mutation in C10orf11. Screening of a cohort of autosomal-recessive-albinism-affected individuals residing in Denmark showed a homozygous 1 bp duplication in C10orf11 in an individual originating from Lithuania. Immunohistochemistry showed localization of C10orf11 in melanoblasts and melanocytes in human fetal tissue, but no localization was seen in retinal pigment epithelial cells. Knockdown of the zebrafish (Danio rerio) homolog with the use of morpholinos resulted in substantially decreased pigmentation and a reduction of the apparent number of pigmented melanocytes. The morphant phenotype was rescued by wild-type C10orf11, but not by mutant C10orf11. In conclusion, we have identified a melanocyte-differentiation gene, C10orf11, which when mutated causes autosomal-recessive albinism in humans.

Isolated complex II deficiency is a rare cause of mitochondrial disease and bi-allelic mutations in SDHB have been identified in only a few patients with complex II deficiency and a progressive neurological phenotype with onset in infancy. On the other hand, heterozygous SDHB mutations are a well-known cause of familial paraganglioma/pheochromocytoma and renal cell cancer. Here, we describe two additional patients with respiratory chain deficiency due to bi-allelic SDHB mutations. The patients’ clinical, neuroradiological, and biochemical phenotype is discussed according to current knowledge on complex II and SDHB deficiency and is well in line with previously described cases, thus confirming the specific neuroradiological presentation of complex II deficiency that recently has emerged. The patients’ genotype revealed one novel SDHB mutation, and one SDHB mutation, which previously has been described in heterozygous form in patients with familial paraganglioma/pheochromocytoma and/or renal cell cancer. This is only the second example in the literature where one specific SDHx mutation is associated with both recessive mitochondrial disease in one patient and familial paraganglioma/pheochromocytoma in others. Due to uncertainties regarding penetrance of different heterozygous SDHB mutations, we argue that all heterozygous SDHB mutation carriers identified in relation to SDHB-related leukoencephalopathy should be referred to relevant surveillance programs for paraganglioma/pheochromocytoma and renal cell cancer. The diagnosis of complex II deficiency due to SDHB mutations therefore raises implications for genetic counselling that go beyond the recurrence risk in the family according to an autosomal recessive inheritance.

Nemaline rods are the pathologic hallmark of nemaline myopathy, but they have also been described as a secondary phenomenon in a variety of other disorders. Nemaline rods have not been reported in pyruvate carboxylase deficiency before. Here we present a patient with pyruvate carboxylase deficiency and nemaline rods detected on muscle biopsy. The nemaline rods may be due to cellular energy shortage and altered energy metabolism in pyruvate carboxylase deficiency, similar to that in the previously reported patients. The mechanism of nemaline rod formation may be associated with the role of pyruvate carboxylase in cellular energy pathways.

Aim: The aim of the study was to identify the genetic background for Aicardi–Goutieres syndrome (AGS) in the Faroe Islands. Methods: Four patients with AGS were identified. The patients had a variable phenotype, from a severe prenatal form with intrauterine foetal death to a milder phenotype, albeit still with an early onset, within the first 2–3 months. Results: A genome-wide search for homozygosity revealed one single 15.6 Mb region of homozygosity on chromosome 13, which included RNASEH2B, where a splice site mutation c.322-3C>G was identified. Screening of 170 anonymous Faroese controls revealed a carrier frequency of approximately 1.8%, corresponding to an incidence of AGS in the Faroe Islands of around 1 in 12 300. Conclusion: The previously identified RNASEH2B mutations comprise altogether 20 mutations (missense, nonsense and splice site) with all patients harbouring at least one missense mutation. The severe phenotype of the Faroese patients compared with the previously reported patients with RNASEH2B mutations may be caused by the presence of two null alleles (although some residual normal splicing cannot be ruled out), whereas patients with one or two missense mutations may have some, albeit abnormal, RNASEH2B proteins, and hence some residual activity of RNASEH2B, explaining their milder phenotype.

Usher syndrome (USH) is the most common genetic disease that causes both deafness and blindness. USH is divided into three types, USH1, USH2 and USH3, depending on the age of onset, the course of the disease, and on the degree of vestibular dysfunction. By homozygosity mapping of a consanguineous Danish family of Dutch descent, we have identified a novel locus for a rare USH3-like syndrome. The affected family members have a unique association of retinitis pigmentosa, progressive hearing impairment, vestibular dysfunction, and congenital cataract. The phenotype is similar, but not identical to that of USH3 patients, as congenital cataract has not been reported for USH3. By homozygosity mapping, we identified a 7.3 Mb locus on chromosome 15q22.2-23 with a maximum multipoint LOD score of 2.0. The locus partially overlaps with the USH1 locus, USH1H, a novel unnamed USH2 locus, and the non-syndromic deafness locus DFNB48.

Background Cone-rod dystrophy is a retinal dystrophy with early loss of cone photoreceptors and a parallel or subsequent loss of rod photoreceptors. It may be syndromic, but most forms are non-syndromic with autosomal dominant, autosomal recessive or X-linked recessive inheritance. Methods and results We identified a small consanguineous family with six patients with cone-rod dystrophy from the Faroe Islands. Homozygosity mapping revealed a single homozygous locus of 4.2 Mb on chromosome 10q23.1–q23.2, encompassing 11 genes. All patients were homozygous for a 1-bp duplication in PCDH21, c.524dupA, which results in a frameshift and a premature stop codon (p.Q175QfsX47). Conclusion To our knowledge, this is the first report of mutations in PCDH21 as a cause of human disease. PCDH21 is highly expressed in the retinal photoreceptor cells. It encodes protocadherin 21, which belongs to the cadherin superfamily of large cell surface proteins characterised by a variable number of extracellular cadherin domains. A PCDH21 knockout mouse model has previously shown loss of photoreceptor cells and abnormal cone and rod function, similar to the findings in the patients.

Mitochondrial DNA depletion, encephalomyopathic form, with methylmalonic aciduria is associated with mutations in SUCLA2, the gene encoding a beta subunit of succinate-CoA ligase, where 17 patients have been reported. Mutations in SUCLG1, encoding the alpha subunit of the enzyme, have been reported in only one family, where a homozygous 2 bp deletion was associated with fatal infantile lactic acidosis. We here report a patient with a novel homozygous missense mutation in SUCLG1, whose phenotype is similar to that of patients with SUCLA2 mutations.

The pyruvate dehydrogenase (PDH) complex is a mitochondrial multienzyme that catalyses the irreversible oxidative decarboxylation of pyruvate to acetyl-CoA. We report four novel PDHA1 mutations in patients with pyruvate dehydrogenase deficiency. Analysis of PDH activity showed decreased activity in fibroblasts from all four patients, around 16-52% of mean control, similar to what has been found in previous studies. Two of the mutations were missense mutations: c.616G>A (p.Glu206Lys) and c.457A>G (p.Met153Val), one was a 3 bp in-frame deletion: c.429_431delAGG (p.Gly143del), and one was a 65 bp duplication: c.900-6_958dup65. cDNA analysis of the 65 bp duplication showed a small amount of normal transcript in addition to the transcript corresponding to the duplication. The small amount of normal transcript likely explains the survival of the patient, who was a boy. The duplication and one of the missense mutations were associated with decreased amounts of E(1)α And E(1)β protein on western blot analysis, whereas the other two mutations were associated with normal amounts. This study adds four novel mutations to the around 90 reported mutations in PDHA1 (HGMD PDHA1 mutation database). The phenotypes of patients with PDH deficiency have been divided into three groups: a neonatal form with severe lactic acidosis, a form observed only in males and characterized by episodes of ataxia with relapses associated with hyperlactataemia, and an infantile form with hypotonia, lethargy, onset of seizures or dystonia, psychomotor retardation, in some cases Leigh-like lesions and mild to moderate hyperlactataemia. The four patients reported here all belong to the latter group, which is the largest.

We describe two brothers with Chudley-McCullough syndrome who are 5 and 17 years old. They were born to healthy consanguineous parents of Pakistani descent. They had severe sensorineural deafness and neuroimaging showed corpus callosum agenesis and other structural brain abnormalities. The Chudley-McCullough syndrome is an autosomal recessive disorder, first described by Chudley et al. [1997: Am J Med Genet 68:350-356]. The original description of the syndrome includes hydrocephalus due to obstruction of the foramen of Monro and early-onset severe to profound sensorineural deafness. We review the findings in the two patients we describe, four children reported in the literature and two patients reported by Hendriks et al. [1999: Am J Med Genet 86:183-186] with sensorineural deafness, corpus callosum agenesis, and interhemispheric cysts, who may well have Chudley-McCullough syndrome. All patients had sensorineural deafness. The neuroimagings of all eight patients showed colpocephaly, which is most likely caused by corpus callosum agenesis. Three patients had other structural brain abnormalities: cortical dysplasia and gray matter heterotopia. We suggest a revision of the clinical description since the most likely basic developmental defect is corpus callosum agenesis and not foramen of Monro obstruction.

Objective: To compare clinical characteristics of patients with sporadic hemiplegic migraine (SHM) with those of patients with migraine with typical aura (MA) and patients with familial hemiplegic migraine (FHM).Methods: The authors used a computer search of Denmark’s National Patient Register to screen the population for patients with migraine with aura with motor weakness, and also examined case records from headache clinics and private practicing neurologists and placed advertisements. The authors screened patients and their relatives with a semi-structured validated telephone interview. All recruited patients were then interviewed by a physician and given a neurologic examination.Results: A total of 105 patients with SHM were identified. Seventy-two percent had four typical aura symptoms: visual, sensory, aphasic, and motor. All had at least two symptoms present during SHM attacks. A gradual progression and sequential appearance of aura symptoms was typical; compared with MA, the duration of each aura symptom was usually prolonged and bilateral motor symptoms were more frequent. Of the patients with SHM, 72% fulfilled the criteria for basilar migraine during SHM attacks. The aura was usually followed by headache, as is common in FHM but not MA.Conclusions: Patients with sporadic hemiplegic migraine had clinical symptoms identical to familial hemiplegic migraine and significantly different from migraine with typical aura. Sporadic hemiplegic migraine is a separate entity, and should be classified with familial hemiplegic migraine.

Recently, two research groups reported that mutations in RMND1 were associated with encephalopathy, elevated lactate, hypotonia, and in some patients seizures or myoclonia in individuals from two consanguineous families. A combined respiratory chain deficiency and a defect in mitochondrial protein translation was found. In this study, we report two siblings who are compound heterozygous for the mutations, c.713A>G and c.1003delG, in RMND1. Respiratory chain enzymatic analysis and BN-PAGE showed a combined OXPHOS deficiency. Western blot analysis indicated normal levels of RMND1, but the assembly of the RMND1 homopolymeric complex was highly impaired. The two siblings had a markedly milder phenotype and longer survival compared to previously reported patients. In addition, they had renal failure and hearing impairment. These two newly described patients contribute to delineation of the clinical spectrum associated with RMND1 aberrations.

3-methylglutaconic aciduria (3-MGA-uria) is a nonspecific finding associated with mitochondrial dysfunction, including defects of oxidative phosphorylation. 3-MGA-uria is classified into five groups, of which one, type IV, is genetically heterogeneous. Here we report five children with a form of type IV 3-MGA-uria characterized by cataracts, severe psychomotor regression during febrile episodes, epilepsy, neutropenia with frequent infections, and death in early childhood. Four of the individuals were of Greenlandic descent, and one was North American, of Northern European and Asian descent. Through a combination of homozygosity mapping in the Greenlandic individuals and exome sequencing in the North American, we identified biallelic variants in the caseinolytic peptidase B homolog (CLPB). The causative variants included one missense variant, c.803C>T (p.Thr268Met), and two nonsense variants, c.961A>T (p.Lys321(∗)) and c.1249C>T (p.Arg417(∗)). The level of CLPB protein was markedly decreased in fibroblasts and liver of affected individuals. CLPB is proposed to function as a mitochondrial chaperone involved in disaggregation of misfolded proteins, resulting from stress such as heat denaturation.

Background: Leigh syndrome is a progressive neurodegenerative disorder, associated with primary or secondary dysfunction of the mitochondrial oxidative phosphorylation. Despite the fact that Leigh syndrome is the most common phenotype of mitochondrial disorders in children, longitudinal natural history data is missing. This study was undertaken to assess the phenotypic and genotypic spectrum of patients with Leigh syndrome, characterise the clinical course and identify predictors of survival in a large cohort of patients. Methods: This is a retrospective study of patients with Leigh syndrome that have been followed at eight centers specialising in mitochondrial diseases in Europe; Gothenburg, Rotterdam, Helsinki, Copenhagen, Stockholm, Brussels, Bergen and Oulu. Results: A total of 130 patients were included (78 males; 52 females), of whom 77 patients had identified pathogenic mutations. The median age of disease onset was 7 months, with 80.8% of patients presenting by the age of 2 years. The most common clinical features were abnormal motor findings, followed by abnormal ocular findings. Epileptic seizures were reported in 40% of patients. Approximately 44% of patients experienced acute exacerbations requiring hospitalisation during the previous year, mainly due to infections. The presence of pathological signs at birth and a history of epileptic seizures were associated with higher occurrence of acute exacerbations and/or relapses. Increased lactate in the cerebrospinal fluid was significantly correlated to a more severe disease course, characterised by early onset before 6 months of age, acute exacerbations and/or relapses, as well as brainstem involvement. 39% of patients had died by the age of 21 years, at a median age of 2.4 years. Disease onset before 6 months of age, failure to thrive, brainstem lesions on neuroimaging and intensive care treatment were significantly associated with poorer survival. Conclusions: This is a multicenter study performed in a large cohort of patients with Leigh syndrome. Our data help define the natural history of Leigh syndrome and identify novel predictors of disease severity and long-term prognosis. publishedVersion

We have investigated seven patients with the type B form of pyruvate carboxylase (PC) deficiency. Mutation analysis revealed eight mutations, all novel. In a patient with exon skipping on cDNA analysis, we identified a homozygous mutation located in a potential branch point sequence, the first possible branch point mutation in PC. Two patients were homozygous for missense mutations (with normal protein amounts on western blot analysis), and two patients were homozygous for nonsense mutations. In addition, a duplication of one base pair was found in a patient who also harboured a splice site mutation. Another splice site mutation led to the activation of a cryptic splice site, shown by cDNA analysis.All patients reported until now with at least one missense mutation have had the milder type A form of PC deficiency. We thus report for the first time two patients with homozygous missense mutations with the severe type B deficiency, clinically indistinguishable from other patients with type B form of PC deficiency.The mutations found here are novel; it is noteworthy that four Turkish patients did not have any mutations in common, despite the rarity of PC deficiency. There is thus no evidence for recurrent mutations in the Turkish or other populations.

Contains fulltext : 81004.pdf (Publisher’s version ) (Closed access) Contiguous gene syndromes affecting the mitochondrial oxidative phosphorylation system have been rarely reported. Here, we describe a patient with apparent mitochondrial encephalomyopathy accompanied by several unusual features, including dysmorphism and hepatopathy, caused by a homozygous triple gene deletion on chromosome 5. The deletion encompassed the NDUFAF2, ERCC8 and ELOVL7 genes, encoding complex I assembly factor 2 (also known as human B17.2L), a protein of the transcription-coupled nucleotide excision repair (TC-NER) machinery, and a putative elongase of very long-chain fatty acid synthesis, respectively. Detailed evaluation of cultured skin fibroblasts revealed disturbed complex I assembly, depolarization of the mitochondrial membrane, elevated cellular NAD(P)H level, increased superoxide production and defective TC-NER. ELOVL7 mRNA was not detectable in these cells and no alterations in fatty acid synthesis were found. By means of baculoviral complementation we were able to restore the aberrations, thereby establishing causative links between genotype and cell-physiological phenotype. This first chromosomal microdeletion illustrates that beside primary defects in mitochondrial genes also additional genes possibly contribute to the disease phenotype, providing an additional explanation for the broad clinical symptoms associated with these disorders.

Fatal infantile lactic acidosis is a severe metabolic disorder characterized by the onset of lactic acidosis within the 1st d of life and early death. We found a combined respiratory-chain enzyme deficiency associated with mitochondrial DNA (mtDNA) depletion in a small consanguineous family with this disorder. To identify the disease-causing gene, we performed single-nucleotide polymorphism homozygosity mapping and found homozygous regions on four chromosomes. DNA sequencing revealed a homozygous 2-bp deletion in SUCLG1, a gene that encodes the alpha subunit of the Krebs-cycle enzyme succinate-coenzyme A ligase (SUCL). The mtDNA depletion is likely explained by decreased mitochondrial nucleoside diphosphate kinase (NDPK) activity resulting from the inability of NDPK to form a complex with SUCL.

We have identified 12 patients with autosomal recessive mitochondrial encephalomyopathy with elevated methylmalonic acid. The disorder has a high incidence of 1 in 1700 in the Faroe Islands due to a founder effect, and a carrier frequency of 1 in 33. The symptoms comprise hypotonia, muscle atrophy, hyperkinesia, severe hearing impairment and postnatal growth retardation. Neuroimaging showed demyelination and central and cortical atrophy, including atrophy of the basal ganglia, and some of the patients fulfilled the criteria for Leigh syndrome. Urine and plasma methylmalonic acid were elevated. Homozygosity mapping with the Affymetrix 10 K array revealed a homozygous region on chromosome 13q14 harbouring the SUCLA2 gene. Mutations in SUCLA2 were recently shown to cause a similar disorder in a small Israeli family. Mutation analysis identified a novel splice site mutation in SUCLA2, IVS4 + 1G --> A, leading to skipping of exon 4. The SUCLA2 gene encodes the ATP-forming beta subunit of the Krebs cycle enzyme succinyl-CoA ligase. The hallmark of the condition, elevated methylmalonic acid, can be explained by an accumulation of the substrate of the enzyme, succinyl-CoA, which in turn leads to elevated methylmalonic acid, because the conversion of methylmalonyl-CoA to succinyl-CoA is inhibited.

We present three patients with SURF1 mutations. In addition to Leigh syndrome all patients had hypertrichosis, a clinical sign that is not usually associated with Leigh syndrome. The hypertrichosis was not congenital and it was mainly distributed on the extremities and forehead. In addition to our three patients, we have identified five patients in the literature with hypertrichosis and Leigh syndrome due to SURF1 mutations. Since most patients had onset of hypertrichosis before the diagnosis of Leigh syndrome was made, we suggest that clinicians consider Leigh syndrome in patients with, for example, psychomotor retardation or other unspecific symptoms in combination with hypertrichosis.

Eiken syndrome is a rare autosomal recessive skeletal dysplasia. We identified a truncation mutation in the C-terminal cytoplasmic tail of the parathyroid hormone (PTH)/PTH-related peptide (PTHrP) type 1 receptor (PTHR1) gene as the cause of this syndrome. Eiken syndrome differs from Jansen and Blomstrand chondrodysplasia and from enchondromatosis, which are all syndromes caused by PTHR1 mutations. Notably, the skeletal features are opposite to those in Blomstrand chondrodysplasia, which is caused by inactivating recessive mutations in PTHR1. To our knowledge, this is the first description of opposite manifestations resulting from distinct recessive mutations in the same gene.

Contains fulltext : 89368.pdf (Publisher’s version ) (Closed access) We investigated the genetic basis for a global and uniform decrease in mitochondrial translation in fibroblasts from patients in two unrelated pedigrees who developed Leigh syndrome, optic atrophy, and ophthalmoplegia. Analysis of the assembly of the oxidative phosphorylation complexes showed severe decreases of complexes I, IV, and V and a smaller decrease in complex III. The steady-state levels of mitochondrial mRNAs, tRNAs, and rRNAs were not reduced, nor were those of the mitochondrial translation elongation factors or the protein components of the mitochondrial ribosome. Using homozygosity mapping, we identified a 1 bp deletion in C12orf65 in one patient, and DNA sequence analysis showed a different 1 bp deletion in the second patient. Both mutations predict the same premature stop codon. C12orf65 belongs to a family of four mitochondrial class I peptide release factors, which also includes mtRF1a, mtRF1, and Ict1, all characterized by the presence of a GGQ motif at the active site. However, C12orf65 does not exhibit peptidyl-tRNA hydrolase activity in an in vitro assay with bacterial ribosomes. We suggest that it might play a role in recycling abortive peptidyl-tRNA species, released from the ribosome during the elongation phase of translation.