Wiedemann-Steiner syndrome as a major cause of syndromic intellectual disability: A study of 33 French cases.

Wiedemann-Steiner syndrome (WSS) is a rare syndromic condition in which intellectual disability (ID) is associated with hypertrichosis cubiti, short stature, and characteristic facies. Following the identification of the causative gene (KMT2A) in 2012, only 31 cases of WSS have been described precisely in the literature. We report on 33 French individuals with a KMT2A mutation confirmed by targeted gene sequencing, high-throughput sequencing or exome sequencing. Patients' molecular and clinical features were recorded and compared with the literature data. On the molecular level, we found 29 novel mutations. We observed autosomal dominant transmission of WSS in 3 families and mosaicism in one family. Clinically, we observed a broad phenotypic spectrum with regard to ID (mild to severe), the facies (typical or not of WSS) and associated malformations (bone, cerebral, renal, cardiac and ophthalmological anomalies). Hypertrichosis cubiti that was supposed to be pathognomonic in the literature was found only in 61% of our cases. This is the largest series of WSS cases yet described to date. A majority of patients exhibited suggestive features, but others were less characteristic, only identified by molecular diagnosis. The prevalence of WSS was higher than expected in patients with ID, suggesting than KMT2A is a major gene in ID.

Clinical and genetic characteristics of xeroderma pigmentosum in Nepal.

BACKGROUND: Little is known about xeroderma pigmentosum (XP) in Himalayan countries. OBJECTIVE: To describe clinical characteristics of XP in Nepal and investigate its genetic bases. METHODS: This study was carried out on all consecutive patients referred for XP to a Nepalese tertiary referral centre in 2014-2015. Clinical data were collected using a standardized questionnaire. DNA was extracted from salivary samples, and next-generation sequencing (NGS) was conducted using a panel covering all 8 known XP genes (classical XP (XP-A to XP-G) and XP variant) and a skin cancer modifier gene, the melanocortin 1 receptor gene (MC1R). RESULTS: Seventeen patients (median age: 15 years; range: 1-32) were included. Twelve had skin cancers (including a total of 8 squamous cell carcinomas, 60 basal cell carcinomas, ocular carcinomas requiring an orbital exenteration in 3 patients, but no melanoma). Fifteen patients carried the same homozygous non-sense XPC mutation c.1243C>T, p.R415X. A homozygous non-sense XPA mutation (p.W235X) was found in the only patient with a history of early severe sunburn reaction and associated neurological symptoms. Associated genetic alterations included heterozygous missense variants in XPD/ERCC2 gene and the presence of MC1R variant R163Q in 5 and 9 patients, respectively. CONCLUSION: Although not previously reported, XP seems frequent in Nepal. Patients often presented with a very severe phenotype after a long history of excessive sun exposure without knowledge of the disease. Fifteen of 17 had the same p.R415X XPC mutation, which seems very specific of XP in Nepal, suggesting a founder effect. NGS analyses frequently revealed associated genetic alterations which could play a modifier role in the clinical expression of the disease.

Brain imaging in mitochondrial respiratory chain deficiency: combination of brain MRI features as a useful tool for genotype/phenotype correlations.

Mitochondrial diseases are characterised by a broad clinical and genetic heterogeneity that makes diagnosis difficult. Owing to the wide pattern of symptoms in mitochondrial disorders and the constantly growing number of disease genes, their genetic diagnosis is difficult and genotype/phenotype correlations remain elusive. Brain MRI appears as a useful tool for genotype/phenotype correlations. Here, we summarise the various combinations of MRI lesions observed in the most frequent mitochondrial respiratory chain deficiencies so as to direct molecular genetic test in patients at risk of such diseases. We believe that the combination of brain MRI features is of value to support respiratory chain deficiency and direct molecular genetic tests.

[Aspect of brain MRI in mitochondrial respiratory chain deficiency. A diagnostic algorithm of the most common mitochondrial genetic mutations]. / Aspect en IRM cérébrale des maladies mitochondriales. Algorithme décisionnel des maladies mitochondriales les plus fréquentes.

Mitochondrial diseases are due to deficiency of the respiratory chain and are characterized by a broad clinical and genetic heterogeneity that makes diagnosis difficult. Some clinical presentations are highly suggestive of given gene mutations, allowing rapid genetic diagnosis. However, owing to the wide pattern of symptoms in mitochondrial disorders and the constantly growing number of disease genes, their genetic diagnosis is frequently difficult and genotype/phenotype correlations remain elusive. For this reason, brain MRI appears as a useful tool for genotype/phenotype correlations. Here, we report the most frequent neuroradiological signs in mitochondrial respiratory chain deficiency and we propose a diagnostic algorithm based on neuroimaging features, so as to direct molecular genetic tests in patients at risk of mitochondrial respiratory chain deficiency. This algorithm is based on the careful analysis of five areas on brain MRI: (1) basal ganglia (hyperintensities on T2 or calcifications); (2) cerebellum (hyperintensities on T2 or atrophy); (3) brainstem (hyperintensities on T2 or atrophy); (4) white matter (leukoencephalopathy); (5) cortex (sub-tentorial atrophy); (6) stroke-like episodes. We believe that the combination of brain MRI features is of value to support respiratory chain deficiency and direct molecular genetic tests.

A constant and similar assembly defect of mitochondrial respiratory chain complex I allows rapid identification of NDUFS4 mutations in patients with Leigh syndrome.

Isolated complex I deficiency is a frequent cause of respiratory chain defects in childhood. In this study, we report our systematic approach with blue native PAGE (BN-PAGE) to study mitochondrial respiratory chain assembly in skin fibroblasts from patients with Leigh syndrome and CI deficiency. We describe five new NDUFS4 patients with a similar and constant abnormal BN-PAGE profile and present a meta-analysis of the literature. All NDUFS4 mutations that have been tested with BN-PAGE result in a constant and similar abnormal assembly profile with a complete loss of the fully assembled complex I usually due to a truncated protein and the loss of its canonical cAMP dependent protein kinase phosphorylation consensus site. We also report the association of abnormal brain MRI images with this characteristic BN-PAGE profile as the hallmarks of NDUFS4 mutations and the first founder NDUFS4 mutations in the North-African population.

A common pattern of brain MRI imaging in mitochondrial diseases with complex I deficiency.

OBJECTIVE: To identify a consistent pattern of brain MRI imaging in primary complex I deficiency. Complex I deficiency, a major cause of respiratory chain dysfunction, accounts for various clinical presentations, including Leigh syndrome. Human complex I comprises seven core subunits encoded by mitochondrial DNA (mtDNA) and 38 core subunits encoded by nuclear DNA (nDNA). Moreover, its assembly requires six known and many unknown assembly factors. To date, no correlation between genotypes and brain MRI phenotypes has been found in complex I deficiencies. DESIGN AND SUBJECTS: The brain MRIs of 30 patients carrying known mutation(s) in genes involved in complex I were retrospectively collected and compared with the brain MRIs of 11 patients carrying known mutations in genes involved in the pyruvate dehydrogenase (PDH) complex as well as 10 patients with MT-TL1 mutations. RESULTS: All complex I deficient patients showed bilateral brainstem lesions (30/30) and 77% (23/30) showed anomalies of the putamen. Supratentorial stroke-like lesions were only observed in complex I deficient patients carrying mtDNA mutations (8/19) and necrotising leucoencephalopathy in patients with nDNA mutations (4/5). Conversely, the isolated stroke-like images observed in patients with MT-TL1 mutations, or the corpus callosum malformations observed in PDH deficient patients, were never observed in complex I deficient patients. CONCLUSION: A common pattern of brain MRI imaging was identified with abnormal signal intensities in brainstem and subtentorial nuclei with lactate peak as a clue of complex I deficiency. Combining clinico-biochemical data with brain imaging may therefore help orient genetic studies in complex I deficiency.

[Strategy in diagnosis of mitochondrial diseases]. / Stratégie diagnostique dans les maladies mitochondriales.

Mitochondrial diseases (MD) are the most frequent metabolic disorders. They have in common a respiratory chain deficiency. Clinical presentation of MD is very heterogeneous and the major physiological functions may be affected. Diagnosis is complex due to the potential involvement of two genomes (nuclear or mitochondrial DNA), the large number of candidate genes to screen and the small number of patients reported for each type of MD. Clinical presentation, trait of inheritance, cerebral imaging (MRI and CT-Scan) and specialized biochemical investigations are good indicators, but identification of causing mutation(s) is the clue to confirm diagnosis. Task is huge and progress in diagnosis of MD should come from genotype-phenotype correlations studies and from major technical improvements in molecular diagnosis. Exhaustive study of mitochondrial DNA is the first necessary step that is now possible with methods like Surveyor and Affymetrix resequencing chip. Combination of data including clinical informations, cerebral imaging, respiratory chain deficiency and/or assembly profile of respiratory chain complexes (BN-PAGE profile) may contribute for orientation for nuclear DNA studies. Elucidation of the genetic bases of MD is important for patients: identification of causing mutation(s) allows offering genetic counselling and possibility of prenatal diagnosis.

Posterior fossa imaging in 158 children with ataxia.

OBJECTIFS: To propose a MRI cerebellar algorithm that may be applied to guide genetic/malformative or biochemical investigations for patients with cerebellar ataxia. PATIENTS AND METHODS: Cerebral MRI of 158 patients with cerebellar ataxia and no supratentorial abnormality were examined according to a new categorization system based on posterior fossa imaging. The clinical and radiological findings were confronted to biochemical and/or genetic results using the MR cerebellar algorithm. Seven groups of cerebellar MRI pattern were described: vermian dysgenesis (n=27), cerebellar hypoplasia (n=15), hemispheric cerebellar dysgenesis (n=6), unilateral hemispheric atrophy (n=5), global cerebellar atrophy (n=84), signal abnormalities (n=11) and normal MRI (n=10). Cerebellar hypoplasia, vermian dysgenesis and hemispheric cerebellar dysgenesis groups were classified as malformative disorders. Global atrophy and signal abnormality groups were classified as metabolic disorders. RESULTS: In the vermian dysgenesis group, a specific genetic diagnosis was obtained in eight children (8/27) and all of the mutated genes (AHI1 (JBS3), CEP290 (JBS5), TMEM67 (JBS6), and RPGRIP1L (JBS7)) are involved in primary cilia function. In the group of pontocerebellar hypoplasia specific genetic diagnosis was obtained in one patient (PCH2) (1/15). Thus, nine of 42 children classified as malformative disorder had a molecular diagnosis. Global atrophy and signal abnormality groups were classified as metabolic disorders, specific biochemical was obtained in 46/95 children. In global atrophy group, respiratory chain deficiency was diagnosed in 18 children (18/84). In 21 children a congenital disorders of glycosylation type 1a (CDG Ia) was diagnosed (21/84) and infantile neuroaxonale dystrophy (INAD) was diagnosed in one child. In signal abnormalities group, specific biochemical diagnosis was obtained in six out of 11 children, five children with respiratory chain deficiency and one child with sulphite oxidase deficiency. In hemispheric cerebellar dysgenesis and normal MRI groups, no biological diagnosis was found for any of the patients. In the group of unilateral hemispheric atrophy, we hypothesized a clastic prenatal injury. CONCLUSION: The proposed MR cerebellar algorithm was useful to guide genetic/malformative or biochemical investigations, allowing an etiological diagnosis in 55 children.

The first founder DGUOK mutation associated with hepatocerebral mitochondrial DNA depletion syndrome.

Deoxyguanosine kinase (dGK) deficiency is a frequent cause of mitochondrial DNA depletion associated with a hepatocerebral phenotype. In this study, we describe a new splice site mutation in the DGUOK gene and the clinical, radiologic, and genetic features of these DGUOK patients. This new DGUOK homozygous mutation (c.444-62C>A) was identified in three patients from two North-African consanguineous families with combined respiratory chain deficiencies and mitochondrial DNA depletion in the liver. Brain MRIs are normal in DGUOK patients in the literature. Interestingly, we found subtentorial abnormal myelination and moderate hyperintensity in the bilateral pallidi in our patients. This new mutation creates a cryptic splice site in intron 3 (in position -62) and is predicted to result in a larger protein with an in-frame insertion of 20 amino acids. In silico analysis of the putative impact of the insertion shows serious clashes in protein conformation: this insertion disrupts the alpha5 helix of the dGK kinase domain, rendering the protein unable to bind purine deoxyribonucleosides. In addition, a common haplotype that segregated with the disease in both families was detected by haplotype reconstruction with 10 markers (microsatellites and SNPs), which span 4.6 Mb of DNA covering the DGUOK locus. In conclusion, we report a new DGUOK splice site mutation that provide insight into a critical protein domain (dGK kinase domain) and the first founder mutation in a North-African population.

Multiple OXPHOS deficiency in the liver of a patient with CblA methylmalonic aciduria sensitive to vitamin B(12).

An adult patient with methylmalonic aciduria due to defective cobalamin synthesis (CblA) responsive to vitamin B(12) presented suddenly with severe visual impairment ascribed to optic atrophy followed by a fatal multiorgan failure and lactic acidosis but low methylmalonic acid in plasma and urine. Multiple deficiency of oxidative phosphorylation was found in the patient's liver. We suggest that patients with B(12)-sensitive methylmalonic aciduria who have a milder clinical course should be carefully monitored for long-term complications.

Spinocerebellar ataxia 7 (SCA7).

Spinocerebellar ataxia 7 (SCA7) is a progressive autosomal dominant neurodegenerative disorder characterized clinically by cerebellar ataxia associated with progressive macular dystrophy. The disease affects primarily the cerebellum and the retina, but also many other CNS structures as the disease progresses. SCA7 is caused by expansion of an unstable trinucleotide CAG repeat encoding a polyglutamine tract in the corresponding protein, ataxin-7. Normal SCA7 alleles contain 4-35 CAG repeats, whereas pathological alleles contain from 36-306 CAG repeats. SCA7 has a number of features in common with other diseases with polyglutamine expansions: (i) the appearance of clinical symptoms above a threshold number of CAG repeats (>35); (ii) a correlation between the size of the expansion and the rate of progression of the disease: the larger the repeat, the faster the progression; (iii) instability of the repeat sequence (approximately 12 CAG/transmission) that accounts for the marked anticipation of approximately 20 years/generation. The CAG repeat sequence is particularly unstable and de novo mutations can occur during paternal transmissions of intermediate size alleles (28-35 CAG repeats). This can explain the persistence of the disease in spite of the anticipation that should have resulted in its extinction.

Normal oxidative phosphorylation in intestinal smooth muscle of childhood chronic intestinal pseudo-obstruction.

BACKGROUND: Chronic intestinal pseudo-obstruction (CIPO) is a severe disease of the digestive tract motility. In pediatric population, CIPO remains of unknown origin for most patients. Chronic intestinal pseudo-obstruction is also a common feature in the course of mitochondrial oxidative phosphorylation disorders related for some patients to mutations in TYMP, POLG1, mtDNA tRNA(leu(UUR)) or tRNA(lys) genes. We hypothesized that CIPOs could be the presenting symptom of respiratory chain enzyme deficiency and thus we investigated oxidative phosphorylation in small bowel and/or colon smooth muscle of primary CIPO children. METHODS: We studied eight children with CIPO and 12 pediatric controls. We collected clinical, radiological and pathological data and measured respiratory chain enzymatic activity in isolated smooth muscle of the small bowel and/or the colon. We also sequenced TYMP, POLG, mtDNA tRNA(leu(UUR)) and tRNA(lys) genes. KEY RESULTS: Neither pathological nor radiological data were in favor of a mitochondrial dysfunction. No respiratory chain enzyme deficiency was detected in CIPO children. In myogenic CIPO, respiratory enzymes and citrate synthase activities were increased in small bowel and/or colon whereas no abnormality was noted in neurogenic and unclassified CIPO. Levels of enzyme activities were higher in control small bowel than in control colon muscle. Sequencing of TYMP, POLG, mtDNA tRNA(leu(UUR)) and tRNA(lys) genes and POLG gene did not reveal mutation for any of the patients. CONCLUSIONS & INFERENCES: The normal enzymatic activities as the lack of radiological and genetic abnormalities indicate that, at variance with adult patients, oxidative phosphorylation deficiency is not a common cause of childhood CIPO.

1H MRS spectroscopy evidence of cerebellar high lactate in mitochondrial respiratory chain deficiency.

Cerebellar ataxia is known to occasionally occur in the course of mitochondrial disorders. We report on MR spectroscopy (1H MRS) evidence of elevated brain lactate in the cerebellar area of 11 patients with cerebellar ataxia ascribed to mitochondrial respiratory chain deficiency (RCD). 1H MRS spectroscopy evidence of lactate peak was found in the cerebellum of 9/11 cases, while no lactate was detected in the putamen in 8/11. We suggest using 1H MRS in cerebellar atrophy in the diagnosis of mitochondrial RCD.

DYT1 mutation in French families with idiopathic torsion dystonia.

A GAG deletion at position 946 in DYT1, one of the genes responsible for autosomal dominant idiopathic torsion dystonia (ITD), has recently been identified. We tested 24 families and six isolated cases with ITD and found 14 individuals from six French families who carried this mutation, indicating that 20% of the affected families carried the DYT1 mutation. Age at onset was always before 20 years (mean, 9+/-4 years). Interestingly, the site of onset was the upper limb in all but one patient. Dystonia was generalized in seven patients and remained focal or segmental in three patients. The absence of common haplotypes among DYT1 families suggests that at least six independent founder mutations have occurred. In addition, one Ashkenazi Jewish family carried the common haplotype described previously in Ashkenazi Jewish patients, but it was absent in the other family. Moreover, the dystonia remained focal in the latter family when compared with the usual generalized phenotype in patients with the common Ashkenazi Jewish haplotype. This indicates that there are at least two founder mutations in this population.

Distribution of ataxin-7 in normal human brain and retina.

Spinocerebellar ataxia 7 (SCA7) is a neurodegenerative disease caused by the expansion of a CAG repeat encoding a polyglutamine tract in the protein ataxin-7. We developed antibodies directed against two different parts of the ataxin-7 protein and studied its distribution in brain and peripheral tissue from healthy subjects. Normal ataxin-7 was widely expressed in brain, retina and peripheral tissues, including striated muscle, testis and thyroid gland. In the brain, expression of ataxin-7 was not limited to areas in which neurones degenerate, and the level of expression was not related to the severity of neuronal loss. Immunoreactivity was low in some vulnerable populations of neurones, such as Purkinje cells. In neurones, ataxin-7 was found in the cell bodies and in processes. Nuclear labelling was also observed in some neurones, but was not related to the distribution of intranuclear inclusions observed in an SCA7 patient. In this patient, the proportion of neurones with nuclear labelling was higher, on average, in regions with neuronal loss. Double immunolabelling coupled with confocal microscopy showed that ataxin-7 colocalized with BiP, a marker of the endoplasmic reticulum, but not with markers of mitochondria or the trans-Golgi network.

Similarities between spinocerebellar ataxia type 7 (SCA7) cell models and human brain: proteins recruited in inclusions and activation of caspase-3.

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant polyglutamine disorder presenting with progressive cerebellar ataxia and blindness. The molecular mechanisms underlying the selective neuronal death typical of SCA7 are unknown. We have established SCA7 cell culture models in HEK293 and SH-SY5Y cells, in order to analyse the effects of overexpression of the mutant ataxin-7 protein. The cells readily formed anti-ataxin-7 positive, fibrillar inclusions and small, nuclear electron dense structures. We have compared the inclusions in cells expressing mutant ataxin-7 and in human SCA7 brain tissue. There were consistent signs of ongoing abnormal protein folding, including the recruitment of heat-shock proteins and proteasome subunits. Occasionally, sequestered transcription factors were found. Activated caspase-3 was recruited into the inclusions in both the cell models and human SCA7 brain and its expression was upregulated in cortical neurones, suggesting that it may play a role in the disease process. Finally, on the ultrastructural level, there were signs of autophagy and nuclear indentations, indicative of a major stress response in cells expressing mutant ataxin-7.

SCA12 is a rare locus for autosomal dominant cerebellar ataxia: a study of an Indian family.

Spinocerebellar ataxia 12 (SCA12) is an autosomal dominant cerebellar ataxia (ADCA) described in a single family with a CAG repeat expansion in the PPP2R2B gene. We screened 247 index cases, including 145 families with ADCA, for this expansion. An expanded repeat ranging from 55 to 61 triplets was detected in 6 affected and 3 unaffected individuals at risk in a single family from India. The association of the PPP2R2B CAG repeat expansion with disease in this new family provides additional evidence that the mutation is causative.

CAG/CTG and CGG/GCC repeats in human brain reference cDNAs: outcome in searching for new dynamic mutations.

CAG and CGG expansion is associated with 10 inherited neurological diseases and is thought to be involved in other human genetic diseases. To identify new candidate genes, we have undertaken a large-scale screening project for CAG/CTG ([CAG]n) and CGG/GCC ([CGG]n) repeats in human brain reference cDNAs. Here, we present the final classification for 597 cDNAs selected by CAG and CGG hybridization from two libraries (100,128 clones) and the updated characterization of [CAG]n- and [CGG]n-positive cDNAs (repeat polymorphism and cDNA localization). We have selected 124 CAG and 83 CGG hybridization-positive clones representing new genes, from which 49 CAG and 7 CGG repeats could be identified. New [CAG]n and [CGG]n with more than seven to nine units were rare (1/2000), and perfect [CAG]n 9 were more likely polymorphic. Overall, highly polymorphic to monomorphic new [CAG]n > 9 and [CGG]n > 7 were characterized. The comparison of our data with other [CAG]n and [CGG]n resources suggests that the screening of reference cDNAs leads to unique sources of new [CAG]n and [CGG]n and will enhance the study of enlarged triplet repeats in human genetic diseases.