Clinical, Neuroimaging, and Metabolic Footprint of the Neurodevelopmental Disorder Caused by Monoallelic HK1 Variants.

Background and Objectives: Hexokinase 1 (encoded by HK1) catalyzes the first step of glycolysis, the adenosine triphosphate-dependent phosphorylation of glucose to glucose-6-phosphate. Monoallelic HK1 variants causing a neurodevelopmental disorder (NDD) have been reported in 12 individuals. Methods: We investigated clinical phenotypes, brain MRIs, and the CSF of 15 previously unpublished individuals with monoallelic HK1 variants and an NDD phenotype. Results: All individuals had recurrent variants likely causing gain-of-function, representing mutational hot spots. Eight individuals (c.1370C>T) had a developmental and epileptic encephalopathy with infantile onset and virtually no development. Of the other 7 individuals (n = 6: c.1334C>T; n = 1: c.1240G>A), 3 adults showed a biphasic course of disease with a mild static encephalopathy since early childhood and an unanticipated progressive deterioration with, e.g., movement disorder, psychiatric disease, and stroke-like episodes, epilepsy, starting in adulthood. Individuals who clinically presented in the first months of life had (near)-normal initial neuroimaging and severe cerebral atrophy during follow-up. In older children and adults, we noted progressive involvement of basal ganglia including Leigh-like MRI patterns and cerebellar atrophy, with remarkable intraindividual variability. The CSF glucose and the CSF/blood glucose ratio were below the 5th percentile of normal in almost all CSF samples, while blood glucose was unremarkable. This biomarker profile resembles glucose transporter type 1 deficiency syndrome; however, in HK1-related NDD, CSF lactate was significantly increased in all patients resulting in a substantially different biomarker profile. Discussion: Genotype-phenotype correlations appear to exist for HK1 variants and can aid in counseling. A CSF biomarker profile with low glucose, low CSF/blood glucose, and high CSF lactate may point toward monoallelic HK1 variants causing an NDD. This can help in variant interpretation and may aid in understanding the pathomechanism. We hypothesize that progressive intoxication and/or ongoing energy deficiency lead to the clinical phenotypes and progressive neuroimaging findings.

A Delphi Survey Study to Formulate Statements on the Treatability of Inherited Metabolic Disorders to Decide on Eligibility for Newborn Screening.

The Wilson and Jungner (W&J) and Andermann criteria are meant to help select diseases eligible for population-based screening. With the introduction of next-generation sequencing (NGS) methods for newborn screening (NBS), more inherited metabolic diseases (IMDs) can technically be included, and a revision of the criteria was attempted. This study aimed to formulate statements and investigate whether those statements could elaborate on the criterion of treatability for IMDs to decide on eligibility for NBS. An online Delphi study was started among a panel of Dutch IMD experts (EPs). EPs evaluated, amended, and approved statements on treatability that were subsequently applied to 10 IMDs. After two rounds of Delphi, consensus was reached on 10 statements. Application of these statements selected 5 out of 10 IMDs proposed for this study as eligible for NBS, including 3 IMDs in the current Dutch NBS. The statement: 'The expected benefit/burden ratio of early treatment is positive and results in a significant health outcome' contributed most to decision-making. Our Delphi study resulted in 10 statements that can help to decide on eligibility for inclusion in NBS based on treatability, also showing that other criteria could be handled in a comparable way. Validation of the statements is required before these can be applied as guidance to authorities.

Generation of three human induced pluripotent stem cell lines, LUMCi024-A, LUMCi025-A, and LUMCi026-A, from two patients with combined oxidative phosphorylation deficiency 8 and a related control.

Combined Oxidative Phosphorylation Deficiency 8 (COXPD8) is an autosomal recessive disorder causing lethal childhood-onset hypertrophic cardiomyopathy. Homozygous or compound heterozygous mutations in the nuclear-encoded mitochondrial alanyl-tRNA synthetase 2 (AARS2) gene underly the pathology. We generated induced pluripotent stem cells (hiPSCs) from two patients carrying the heterozygous compound c.1774 C>T, c.2188 G>A and c.2872 C>T AARS2 mutations, as well as a related healthy control carrying the c.2872 C>T AARS2 mutation. All hiPSC-lines expressed pluripotency markers, maintained a normal karyotype, and differentiated towards the three germ layer derivatives in vitro. These lines can be used to model COXPD8 or mitochondrial dysfunction.

The impact of gender, puberty, and pregnancy in patients with POLG disease.

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.

Autosomal recessive limb-girdle and Miyoshi muscular dystrophies in the Netherlands: The clinical and molecular spectrum of 244 patients.

In this retrospective study, we conducted a clinico-genetic analysis of patients with autosomal recessive limb-girdle muscular dystrophy (LGMD) and Miyoshi muscular dystrophy (MMD). Patients were identified at the tertiary referral centre for DNA diagnosis in the Netherlands and included if they carried two mutations in CAPN3, DYSF, SGCG, SGCA, SGCB, SGCD, TRIM32, FKRP or ANO5 gene. DNA was screened by direct sequencing and multiplex ligand-dependent probe amplification (MLPA) analysis. A total of 244 patients was identified; 68 LGMDR1/LGMD2A patients with CAPN3 mutations (28%), 67 sarcoglycanopathy patients (LGMDR3-5/LGMD2C-E) (27%), 64 LGMDR12/LGMD2L and MMD3 patients with ANO5 mutations (26%), 25 LGMDR2/LGMD2B and MMD1 with DYSF mutations (10%), 21 LGMDR9/LGMD2I with FKRP mutations (9%) and one LGMDR8/LGMD2H patient with TRIM32 mutations (<1%). The estimated minimum prevalence of AR-LGMD and MMD in the Netherlands amounted to 14.4 × 10-6 . Thirty-three novel mutations were identified. A wide range in age of onset (0-72 years) and loss of ambulation (5-74 years) was found. Fifteen patients (6%) initially presented with asymptomatic hyperCKemia. Cardiac abnormalities were found in 35 patients (17%). Non-invasive ventilation was started in 34 patients (14%). Both cardiac and respiratory involvement occurs across all subtypes, stressing the need for screening in all included subtypes.

Molybdenum cofactor deficiency: Identification of a patient with homozygote mutation in the MOCS3 gene.

We describe the clinical presentation and 17 years follow up of a boy, born to consanguineous parents and presenting with intellectual disability (ID), autism, "marfanoid" dysmorphic features, and moderate abnormalities of sulfite metabolism compatible with molybdenum cofactor deficiency, but normal sulfite oxidase activity in cultured skin fibroblasts. Genomic exome analysis revealed a homozygous MOCS3 missense mutation, leading to a p.Ala257Thr substitution in the highly conserved ubiquitin-like-domain of the protein. MOCS3 is the third protein, besides MOCS1 and MOCS2, involved in the biosynthesis of the molybdenum cofactor and has a dual ubiquitin-like function in tRNA thiolation. It is plausible that the phenotype results from deficiency of this dual function, not only from defective synthesis of molybdenum cofactor, which would explain similarities and differences from the MOCS1 and MOCS2-related disorders. This observation should encourage testing of additional ID patients with mild abnormalities of sulfite metabolism for MOCS3 mutations.

Succinate-CoA ligase deficiency due to mutations in SUCLA2 and SUCLG1: phenotype and genotype correlations in 71 patients.

BACKGROUND: The encephalomyopathic mtDNA depletion syndrome with methylmalonic aciduria is associated with deficiency of succinate-CoA ligase, caused by mutations in SUCLA2 or SUCLG1. We report here 25 new patients with succinate-CoA ligase deficiency, and review the clinical and molecular findings in these and 46 previously reported patients. PATIENTS AND RESULTS: Of the 71 patients, 50 had SUCLA2 mutations and 21 had SUCLG1 mutations. In the newly-reported 20 SUCLA2 patients we found 16 different mutations, of which nine were novel: two large gene deletions, a 1 bp duplication, two 1 bp deletions, a 3 bp insertion, a nonsense mutation and two missense mutations. In the newly-reported SUCLG1 patients, five missense mutations were identified, of which two were novel. The median onset of symptoms was two months for patients with SUCLA2 mutations and at birth for SUCLG1 patients. Median survival was 20 years for SUCLA2 and 20 months for SUCLG1. Notable clinical differences between the two groups were hepatopathy, found in 38% of SUCLG1 cases but not in SUCLA2 cases, and hypertrophic cardiomyopathy which was not reported in SUCLA2 patients, but documented in 14% of cases with SUCLG1 mutations. Long survival, to age 20 years or older, was reported in 12% of SUCLA2 and in 10% of SUCLG1 patients. The most frequent abnormality on neuroimaging was basal ganglia involvement, found in 69% of SUCLA2 and 80% of SUCLG1 patients. Analysis of respiratory chain enzyme activities in muscle generally showed a combined deficiency of complexes I and IV, but normal histological and biochemical findings in muscle did not preclude a diagnosis of succinate-CoA ligase deficiency. In five patients, the urinary excretion of methylmalonic acid was only marginally elevated, whereas elevated plasma methylmalonic acid was consistently found. CONCLUSIONS: To our knowledge, this is the largest study of patients with SUCLA2 and SUCLG1 deficiency. The most important findings were a significantly longer survival in patients with SUCLA2 mutations compared to SUCLG1 mutations and a trend towards longer survival in patients with missense mutations compared to loss-of-function mutations. Hypertrophic cardiomyopathy and liver involvement was exclusively found in patients with SUCLG1 mutations, whereas epilepsy was much more frequent in patients with SUCLA2 mutations compared to patients with SUCLG1 mutations. The mutation analysis revealed a number of novel mutations, including a homozygous deletion of the entire SUCLA2 gene, and we found evidence of two founder mutations in the Scandinavian population, in addition to the known SUCLA2 founder mutation in the Faroe Islands.

The expanding phenotype of COL4A1 and COL4A2 mutations: clinical data on 13 newly identified families and a review of the literature.

Two proα1(IV) chains, encoded by COL4A1, form trimers that contain, in addition, a proα2(IV) chain encoded by COL4A2 and are the major component of the basement membrane in many tissues. Since 2005, COL4A1 mutations have been known as an autosomal dominant cause of hereditary porencephaly. COL4A1 and COL4A2 mutations have been reported with a broader spectrum of cerebrovascular, renal, ophthalmological, cardiac, and muscular abnormalities, indicated as "COL4A1 mutation-related disorders." Genetic counseling is challenging because of broad phenotypic variation and reduced penetrance. At the Erasmus University Medical Center, diagnostic DNA analysis of both COL4A1 and COL4A2 in 183 index patients was performed between 2005 and 2013. In total, 21 COL4A1 and 3 COL4A2 mutations were identified, mostly in children with porencephaly or other patterns of parenchymal hemorrhage, with a high de novo mutation rate of 40% (10/24). The observations in 13 novel families harboring either COL4A1 or COL4A2 mutations prompted us to review the clinical spectrum. We observed recognizable phenotypic patterns and propose a screening protocol at diagnosis. Our data underscore the importance of COL4A1 and COL4A2 mutations in cerebrovascular disease, also in sporadic patients. Follow-up data on symptomatic and asymptomatic mutation carriers are needed for prognosis and appropriate surveillance.

Germline activating AKT3 mutation associated with megalencephaly, polymicrogyria, epilepsy and hypoglycemia.

Activating germ-line and somatic mutations in AKT3 (OMIM 611223) are associated with megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome (MPPH; OMIM # 615937) and megalencephaly-capillary malformation (MCAP; OMIM # 602501). Here we report an individual with megalencephaly, polymicrogyria, refractory epilepsy, hypoglycemia and a germline AKT3 mutation. At birth, head circumference was 43 cm (5 standard deviations above the mean). No organomegaly was present, but there was generalized hypotonia, joint and skin laxity, developmental delay and failure to thrive. At 6 months of age the patient developed infantile spasms that were resistant to antiepileptic polytherapy. Recurrent hypoglycemia was noted during treatment with adrenocorticotropic hormone but stabilized upon introduction of continuous, enriched feeding. The infantile spasms responded to the introduction of a ketogenic diet, but the hypoglycemia recurred until the diet was adjusted for increased resting energy expenditure. A novel, de novo AKT3 missense variant (exon 5; c.548T>A, p.(V183D)) was identified and shown to activate AKT3 by in vitro functional testing. We hypothesize that the sustained hypoglycemia in this patient is caused by increased glucose utilization due to activation of AKT3 signaling. This might explain the efficacy of the ketogenic diet in this individual.

Severe presentation of WDR62 mutation: is there a role for modifying genetic factors?

Mutations in WDR62 are associated with primary microcephaly; however, they have been reported with wide phenotypic variability. We report on six individuals with novel WDR62 mutations who illustrate this variability and describe three in greater detail. Of the three, one lacks neuromotor development and has severe pachygyria on MRI, another has only delayed speech and motor development and moderate polymicrogyria, and the third has an intermediate phenotype. We observed a rare copy number change of unknown significance, a 17q25qter duplication, in the first severely affected individual. The 17q25 duplication included an interesting candidate gene, tubulin cofactor D (TBCD), crucial in microtubule assembly and disassembly. Sequencing of the non-duplicated allele showed a TBCD missense mutation, predicted to cause a deleterious p.Phe1121Val substitution. Sequencing of a cohort of five patients with WDR62 mutations, including one with an identical mutation and different phenotype, plus 12 individuals with diagnosis of microlissencephaly and another individual with mild intellectual disability (ID) and a 17q25 duplication, did not reveal TBCD mutations. However, immunostaining with tubulin antibodies of cells from patients with both WDR62 and TBCD mutation showed abnormal tubulin network when compared to controls and cells with only the WDR62 mutation. Therefore, we propose that genetic factors contribute to modify the severity of the WDR62 phenotype and, although based on suggestive evidence, TBCD could function as one of such factors.

ACTA2 mutation with childhood cardiovascular, autonomic and brain anomalies and severe outcome.

Thoracic aortic aneurysm and dissection (TAAD) are associated with connective tissue disorders like Marfan syndrome and Loeys-Dietz syndrome, caused by mutations in the fibrillin-1, the TGFß-receptor 1- and -2 genes, the SMAD3 and TGFß2 genes, but have also been ascribed to ACTA2 gene mutations in adults, spread throughout the gene. We report on a novel de novo c.535C>T in exon 6 leading to p.R179C aminoacid substitution in ACTA2 in a toddler girl with primary pulmonary hypertension, persistent ductus arteriosus, extensive cerebral white matter lesions, fixed dilated pupils, intestinal malrotation, and hypotonic bladder. Recently, de novo ACTA2 R179H substitutions have been associated with a similar phenotype and additional cerebral developmental defects including underdeveloped corpus callosum and vermis hypoplasia in a single patient. The patient here shows previously undescribed abnormal lobulation of the frontal lobes and position of the gyrus cinguli and rostral dysplasis of the corpus callosum; she died at the age of 3 years during surgery due to vascular fragility and rupture of the ductus arteriosus. Altogether these observations support a role of ACTA2 in brain development, especially related to the arginine at position 179. Although all previously reported patients with R179H substitution successfully underwent the same surgery at younger ages, the severe outcome of our patient warns against the devastating effects of the R179C substitution on vasculature.

Exome sequencing reveals a novel Moroccan founder mutation in SLC19A3 as a new cause of early-childhood fatal Leigh syndrome.

Leigh syndrome is an early onset, often fatal progressive neurodegenerative disorder caused by mutations in the mitochondrial or nuclear DNA. Until now, mutations in more than 35 genes have been reported to cause Leigh syndrome, indicating an extreme genetic heterogeneity for this disorder, but still only explaining part of the cases. The possibility of whole exome sequencing enables not only mutation detection in known candidate genes, but also the identification of new genes associated with Leigh syndrome in small families and isolated cases. Exome sequencing was combined with homozygosity mapping to identify the genetic defect in a Moroccan family with fatal Leigh syndrome in early childhood and specific magnetic resonance imaging abnormalities in the brain. We detected a homozygous nonsense mutation (c.20C>A; p.Ser7Ter) in the thiamine transporter SLC19A3. In vivo overexpression of wild-type SLC19A3 showed an increased thiamine uptake, whereas overexpression of mutant SLC19A3 did not, confirming that the mutation results in an absent or non-functional protein. Seventeen additional patients with Leigh syndrome were screened for mutations in SLC19A3 using conventional Sanger sequencing. Two unrelated patients, both from Moroccan origin and one from consanguineous parents, were homozygous for the same p.Ser7Ter mutation. One of these patients showed the same MRI abnormalities as the patients from the first family. Strikingly, patients receiving thiamine had an improved life-expectancy. One patient in the third family deteriorated upon interruption of the thiamine treatment and recovered after reinitiating. Although unrelated, all patients came from the province Al Hoceima in Northern Morocco. Based on the recombination events the mutation was estimated to have occurred 1250-1750 years ago. Our data shows that SLC19A3 is a new candidate for mutation screening in patients with Leigh syndrome, who might benefit from high doses of thiamine and/or biotin. Especially, Moroccan patients with Leigh syndrome should be tested for the c.20C>A founder mutation in SLC19A3.

COX19 mediates the transduction of a mitochondrial redox signal from SCO1 that regulates ATP7A-mediated cellular copper efflux.

SCO1 and SCO2 are metallochaperones whose principal function is to add two copper ions to the catalytic core of cytochrome c oxidase (COX). However, affected tissues of SCO1 and SCO2 patients exhibit a combined deficiency in COX activity and total copper content, suggesting additional roles for these proteins in the regulation of cellular copper homeostasis. Here we show that both the redox state of the copper-binding cysteines of SCO1 and the abundance of SCO2 correlate with cellular copper content and that these relationships are perturbed by mutations in SCO1 or SCO2, producing a state of apparent copper overload. The copper deficiency in SCO patient fibroblasts is rescued by knockdown of ATP7A, a trans-Golgi, copper-transporting ATPase that traffics to the plasma membrane during copper overload to promote efflux. To investigate how a signal from SCO1 could be relayed to ATP7A, we examined the abundance and subcellular distribution of several soluble COX assembly factors. We found that COX19 partitions between mitochondria and the cytosol in a copper-dependent manner and that its knockdown partially rescues the copper deficiency in patient cells. These results demonstrate that COX19 is necessary for the transduction of a SCO1-dependent mitochondrial redox signal that regulates ATP7A-mediated cellular copper efflux.

Non-random mtDNA segregation patterns indicate a metastable heteroplasmic segregation unit in m.3243A>G cybrid cells.

Many pathogenic mitochondrial DNA mutations are heteroplasmic, with a mixture of mutated and wild-type mtDNA present within individual cells. The severity and extent of the clinical phenotype is largely due to the distribution of mutated molecules between cells in different tissues, but mechanisms underpinning segregation are not fully understood. To facilitate mtDNA segregation studies we developed assays that measure m.3243A>G point mutation loads directly in hundreds of individual cells to determine the mechanisms of segregation over time. In the first study of this size, we observed a number of discrete shifts in cellular heteroplasmy between periods of stable heteroplasmy. The observed patterns could not be parsimoniously explained by random mitotic drift of individual mtDNAs. Instead, a genetically metastable, heteroplasmic mtDNA segregation unit provides the likely explanation, where stable heteroplasmy is maintained through the faithful replication of segregating units with a fixed wild-type/m.3243A>G mutant ratio, and shifts occur through the temporary disruption and re-organization of the segregation units. While the nature of the physical equivalent of the segregation unit remains uncertain, the factors regulating its organization are of major importance for the pathogenesis of mtDNA diseases.

COL4A2 mutation associated with familial porencephaly and small-vessel disease.

Familial porencephaly, leukoencephalopathy and small-vessel disease belong to the spectrum of disorders ascribed to dominant mutations in the gene encoding for type IV collagen alpha-1 (COL4A1). Mice harbouring mutations in either Col4a1 or Col4a2 suffer from porencephaly, hydrocephalus, cerebral and ocular bleeding and developmental defects. We observed porencephaly and white matter lesions in members from two families that lack COL4A1 mutations. We hypothesized that COL4A2 mutations confer genetic predisposition to porencephaly, therefore we sequenced COL4A2 in the family members and characterized clinical, neuroradiological and biochemical phenotypes. Genomic sequencing of COL4A2 identified the heterozygous missense G1389R in exon 44 in one family and the c.3206delC change in exon 34 leading to frame shift and premature stop, in the second family. Fragmentation and duplication of epidermal basement membranes were observed by electron microscopy in a c.3206delC patient skin biopsy, consistent with abnormal collagen IV network. Collagen chain accumulation and endoplasmic reticulum (ER) stress have been proposed as cellular mechanism in COL4A1 mutations. In COL4A2 (3206delC) fibroblasts we detected increased rates of apoptosis and no signs of ER stress. Mutation phenotypes varied, including porencephaly, white matter lesions, cerebellar and optic nerve hypoplasia and unruptured carotid aneurysm. In the second family however, we found evidence for additional factors contributing to the phenotype. We conclude that dominant COL4A2 mutations are a novel major risk factor for familial cerebrovascular disease, including porencephaly and small-vessel disease with reduced penetrance and variable phenotype, which might also be modified by other contributing factors.

Nonsense mutations in CABC1/ADCK3 cause progressive cerebellar ataxia and atrophy.

Hereditary ataxias are genetic disorders characterized by uncoordinated gait and often poor coordination of hands, speech, and eye movements. Frequently, atrophy of the cerebellum occurs. Many ataxias are autosomal dominant, but autosomal recessive (AR) disease occurs as well. Homozygosity mapping in a consanguineous family with three affected children with progressive cerebellar ataxia and atrophy revealed a candidate locus on chromosome 1, containing the CABC1/ADCK3 (the chaperone, ABC1 activity of bc1 complex homologue) gene. CABC1/ADCK3 is the homologue of the yeast Coq8 gene, which is involved in the ubiquinone biosynthesis pathway. Mutation analysis of this gene showed a homozygous nonsense mutation (c.1042C>T, p.R348X). Eight additional patients with AR cerebellar ataxia and atrophy were screened for mutations in the CABC1/ADCK3 gene. One patient was compound heterozygous for the same c.1042C>T mutation and a second nonsense mutation (c.1136T>A, p.L379X). Both mutations created a premature stop codon, triggering nonsense mediated mRNA decay as the pathogenic mechanism. We found no evidence of a Dutch founder for the c.1042C>T mutation in AR ataxia. We report here the first nonsense mutations in CABC1 that most likely lead to complete absence of a functional CABC1 protein. Our results indicate that CABC1 is an important candidate for mutation analysis in progressive cerebellar ataxia and atrophy on MRI to identify those patients, who may benefit from CoQ10 treatment.

Aortic distensibility alterations in adults with m.3243A>G MELAS gene mutation.

PRINCIPLES: MELAS, or mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes is a new distinctive clinical entity. The current study was designed to assess ascending aortic elasticity in adult patients with MELAS syndrome and in gene carriers, and to compare the results with age- and gender-matched healthy controls. METHODS: The study comprised eight patients with MELAS syndrome and four asymptomatic gene carriers. All subjects underwent complete 2-dimensional transthoracic echocardiography, and systolic and diastolic ascending aortic diameters (SD and DD respectively) were recorded in M-mode 3 cm above the aortic valve from a parasternal long-axis view. Aortic elastic properties were calculated using aortic data and forearm blood pressure values. RESULTS: SD and DD of MELAS patients and gene carriers were enlarged compared with controls. Aortic stiffness index was increased (16.4+/-3.7 vs 3.6+/-1.1, p=0.00001), while aortic strain (0.035+/-0.012% vs 0.146+/-0.050%, p=0.00002) and aortic distensibility (1.03+/-0.30 cm2/dynes 10(-6) vs 4.70+/-1.69 cm2/dynes 10(-6), p=0.0002) were decreased in MELAS patients compared with controls. Aortic elastic properties of gene carriers were between MELAS patients and controls. CONCLUSIONS: Increased ascending aortic stiffness and enlarged aortic dimensions suggesting vascular remodelling were found in MELAS patients as compared with controls.

Phenotypic consequences of a novel SCO2 gene mutation.

SCO2 is a cytochrome c oxidase (COX) assembly gene. Mutations in the SCO2 gene have been associated with fatal infantile cardioencephalomyopathy. We report on the phenotype of a novel SCO2 mutation in two siblings with fatal infantile cardioencephalomyopathy. The index patient died of heart failure at 25 days of age. Muscle biopsy was performed for histology and biochemical study of the oxidative phosphorylation system complexes. The entire coding region of the SCO2 gene was sequenced. Autopsy was performed on the index patient and on a female sibling delivered at 23 weeks of gestation following termination of pregnancy during which amniocentesis and genetic testing had been performed. Muscle biopsy and biochemical analysis of heart and skeletal muscle detected a severe isolated COX-IV deficiency. Pathologic findings in both patients confirmed hypertrophic cardiomyopathy. Sequencing of the SCO2 gene showed compound heterozygous mutation; the common E140K mutation and a novel W36X nonsense mutation. Newborns with a combination of hypotonia and cardiomyopathy should be evaluated for multiple congenital anomaly syndromes, inborn errors of metabolism and mitochondrial derangements, and may require extensive diagnostic testing. Mutations in the SCO2 gene are a cause of prenatal-onset hypertrophic cardiomyopathy.