Myopathy with MTCYB mutation mimicking Multiple Acyl-CoA Dehydrogenase Deficiency.

We describe two patients with mitochondrial DNA mutations in the gene encoding cytochrome b (m.15579A>G, p.Tyr278Cys and m.15045G>A p.Arg100Gln), which presented as a pure myopathic form (exercise intolerance), with an onset in childhood. Diagnosis was delayed, because acylcarnitine profile showed an increase in medium and long-chain acylcarnitines, suggestive of multiple acyl-CoA dehydrogenase deficiency, riboflavin transporter deficiency or FAD metabolism disorder. Implication of cytochrome b in fatty acid oxidation, and physiopathology of the mutations are discussed.

Mutation update and uncommon phenotypes in a French cohort of 96 patients with WFS1-related disorders.

WFS1 mutations are responsible for Wolfram syndrome (WS) characterized by juvenile-onset diabetes mellitus and optic atrophy, and for low-frequency sensorineural hearing loss (LFSNHL). Our aim was to analyze the French cohort of 96 patients with WFS1-related disorders in order (i) to update clinical and molecular data with 37 novel affected individuals, (ii) to describe uncommon phenotypes and, (iii) to precise the frequency of large-scale rearrangements in WFS1. We performed quantitative polymerase chain reaction (PCR) in 13 patients, carrying only one heterozygous variant, to identify large-scale rearrangements in WFS1. Among the 37 novel patients, 15 carried 15 novel deleterious putative mutations, including one large deletion of 17,444 base pairs. The analysis of the cohort revealed unexpected phenotypes including (i) late-onset symptoms in 13.8% of patients with a probable autosomal recessive transmission; (ii) two siblings with recessive optic atrophy without diabetes mellitus and, (iii) six patients from four families with dominantly-inherited deafness and optic atrophy. We highlight the expanding spectrum of WFS1-related disorders and we show that, even if large deletions are rare events, they have to be searched in patients with classical WS carrying only one WFS1 mutation after sequencing.

An overview of neurological and neuromuscular signs in mitochondrial diseases.

Mitochondrial disorders have a broad clinical spectrum and are genetically heterogeneous, involving two genomes. These disorders may be develop at any age, with isolated or multiple system involvement, and any pattern of inheritance. Neurological involvement is the most frequent, and concerns muscular, peripheral and central nervous system. Among these diverse signs, some are suggestive of mitochondrial disease, such as progressive external ophthalmoplegia, exercise intolerance, psychomotor regression, stroke-like episodes, refractory epilepsy and Epilepsia Partialis Continua. Others are less specific and mitochondrial hypothesis may be evocated because of either association of different neuromuscular signs or a multisystemic involvement. This review describes the wealth of this neurological and neuromuscular symptomatology through different syndromes reported in the literature, according to preponderant signs and to modes of inheritance, as key elements to guide genetics testing.

[Bladder-sphincter disorders associated with Wolfram syndrome]. / Troubles vésicosphinctériens au cours du syndrome de Wolfram.

OBJECTIVES: To identify and describe functional urinary symptoms, uro-nephrological complications and their impact on quality of life in a cohort of patients diagnosed with the Wolfram syndrome (SW). PATIENTS AND METHODS: A transversal descriptive patient's cohort study was performed. The Urinary Symptom Profile (USP) and the International Consultation Incontinence Questionnaire - Female Lower Urinary Tracts Symptoms (ICIQ-FLUTS) were used to evaluate urinary symptoms and their impact on quality of life through direct interviews conducted by telephone. A less than 6-month old renal ultrasound and serum creatinine results were asked to the patient or physician. RESULTS: Thirty-three patients have been contacted and 22 (73%) agreed to participate in this study. Eighteen patients over 22 had spontaneous micturition when four of them had an urinary diversion (two definitive, two temporaries) before being included in this study. Seventy-three percent of patients with spontaneous micturition had urinary symptoms. A severe or moderate symptoms score was noted in 67% (12/18 patients) and 11% (2/18 patients) respectively. CONCLUSION: Functional urinary dysfunctions were frequent and impacted quality of life in more than one half of patients diagnosed with SW in this study. Early diagnostic and regular urological follow-up can improve the quality of life and prevent severe urinary complications.

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.

The severity of phenotype linked to SUCLG1 mutations could be correlated with residual amount of SUCLG1 protein.

BACKGROUND: Succinate-CoA ligase deficiency is responsible for encephalomyopathy with mitochondrial DNA depletion and mild methylmalonic aciduria. Mutations in SUCLA2, the gene encoding a ß subunit of succinate-CoA ligase, have been reported in 17 patients until now. Mutations in SUCLG1, encoding the α subunit of the enzyme, have been described in two pedigrees only. METHODS AND FINDINGS: In this study, two unrelated patients harbouring three novel pathogenic mutations in SUCLG1 were reported. The first patient had a severe disease at birth. He was compound heterozygous for a missense mutation (p.Pro170Arg) and a c.97+3G>C mutation, which leads to the complete skipping of exon 1 in a minigene expression system. The involvement of SUCLG1 was confirmed by western blot analysis, which showed absence of SUCLG1 protein in fibroblasts. The second patient has a milder phenotype, similar to that of patients with SUCLA2 mutations, and is still alive at 12 years of age. Western blot analysis showed some residual SUCLG1 protein in patient's fibroblasts. CONCLUSIONS: Our results suggest that SUCLG1 mutations that lead to complete absence of SUCLG1 protein are responsible for a very severe disorder with antenatal manifestations, whereas a SUCLA2-like phenotype is found in patients with residual SUCLG1 protein. Furthermore, it is shown that in the absence of SUCLG1 protein, no SUCLA2 protein is found in fibroblasts by western blot analysis. This result is consistent with a degradation of SUCLA2 when its heterodimer partner, SUCLG1, is absent.

Molecular diagnosis and genetic counseling for spinal muscular atrophy (SMA).

Spinal muscular atrophy (SMA) is a neuromuscular autosomal recessive disorder caused by bi-allelic pathogenic variants in the SMN1 gene. 95% of SMA patients have a SMN1 homozygous deletion. In the 5% remaining affected patients, a heterozygous SMN1 deletion is associated with an intragenic SMN1 rare inactivating pathogenic variant on the other allele. The clinical phenotype of SMA is heterogeneous and severity is inversely correlated with the number of SMN2 copies, a non-functional SMN1 copy. The development of new treatments leads to the generalization of carrier and newborn screening in many countries and new robust and low cost methods for large population-based screening have been developed. It is important that all diagnosed patients and relatives receive appropriate genetic counseling, taking into account the great complexity of SMA region to avoid pitfalls. © 2020 French Society of Pediatrics. Published by Elsevier Masson SAS. All rights reserved.

Rapid identification of mitochondrial DNA (mtDNA) mutations in neuromuscular disorders by using surveyor strategy.

Mutations of mitochondrial genome are responsible for respiratory chain defects in numerous patients. We have used a strategy, based on the use of a mismatch-specific DNA endonuclease named " Surveyor Nuclease", for screening the entire mtDNA in a group of 50 patients with neuromuscular features, suggesting a respiratory chain dysfunction. We identified mtDNA mutations in 20% of patients (10/50). Among the identified mutations, four are not found in any mitochondrial database and have not been reported previously. We also confirm that mtDNA polymorphisms are frequently found in a heteroplasmic state (15 different polymorphisms were identified among which five were novel).

Autosomal dominant transmission of diabetes and congenital hearing impairment secondary to a missense mutation in the WFS1 gene.

AIMS: Mutations of the WFS1 gene have been implicated in autosomal dominant diseases, such as low-frequency sensorineural hearing impairment (LFSNHI) and/or diabetes mellitus and/or optic atrophy. The aim was to investigate WFS1 gene sequences in a family with diabetes mellitus and hearing impairment. METHODS: Three members of a family with a maternally inherited combination of diabetes mellitus and hearing impairment, but no specific mutations in its mitochondrial genome, were investigated for mutations in the WFS1 gene. RESULTS: This pedigree, in which the proband had non-insulin-dependent diabetes mellitus and congenital hearing impairment and his mother a triple combination of diabetes mellitus, hearing impairment and optic atrophy, was found to be associated with autosomal dominant transmission of the E864K mutation of the WFS1 gene. CONCLUSIONS: In the light of this confirmatory study, we recommend the systematic analysis of WFS1 gene sequences in patients with parentally inherited diabetes mellitus and deafness (+/- optic atrophy), in particular when diabetogenic mtDNA mutations have been excluded.

Expression in transgenic mice of the large T antigen of polyomavirus induces Sertoli cell tumours and allows the establishment of differentiated cell lines.

The large T antigen of polyomavirus (PyLT) efficiently immortalizes rodent fibroblasts, but, unlike SV40 T antigen, it is not sufficient to achieve complete oncogenic transformation. We analysed a series of transgenic mouse families that express the PyLT protein under control of the viral enhancer-promoter region. In all of them, the transgene was expressed in the seminiferous epithelium of the testis (Sertoli and germ cells), with no pathological consequences during most of the animals' lives. However, every old male developed large bilateral tumours of the testes, generated by the proliferation of Sertoli cell derivatives. Cell lines could be readily established both from the tumours and from the still apparently normal testis before the onset of tumoral growth. They retained in vitro morphological and ultrastructural features characteristic of Sertoli cells. But, in addition to this major Sertoli component, the maintenance of a cellular contingent of germinal origin was suggested by the expression of genes that are normally transcribed during the premeiotic and early meiotic stages of spermatogenesis (LDH-X, Hox1.4 and c-kit). The two cell types remained tightly associated, even at late passages in culture, and could not be separated by conventional cloning procedures. This association in culture of the two cell types whose interaction is critical for spermatogenesis may provide a useful tool for its molecular analysis.

Molecular and functional effects of the T14709C point mutation in the mitochondrial DNA of a patient with maternally inherited diabetes and deafness.

A heteroplasmic T to C transition at nucleotide position 14709 in the mitochondrial tRNA glutamic acid (tRNA(Glu)) gene has previously been associated with maternally inherited diabetes and deafness (MIDD). To investigate the pathogenic mechanism of the T14709C mutation, we have constructed transmitochondrial cell lines by transferring fibroblasts mitochondria from a patient with the mutation into human cells lacking mitochondrial DNA (mtDNA) (rho degrees cells). Clonal cybrid cell lines were obtained containing various levels of the heteroplasmic mutation, or exclusively mutated or wild-type mtDNA. Measurement of respiratory chain enzymatic activities failed to detect a difference between the homoplasmic mutant and homoplasmic wild-type cybrid cell lines. However, a subtle decrease in the steady-state levels of tRNA(Glu) transcripts in some mutant clones. Our studies suggest that the T14709C mutation is insufficient to lead impairment of mitochondrial function in homoplasmic osteosarcoma cybrid clones, and that we cannot exclude that the T14709C mutation affects mitochondrial function by a yet unidentified mechanism.

[Cytochrome c oxydase-deficient Leigh syndrome with homozygous mutation in SURF1 gene]. / Syndrome de Leigh avec déficit en cytochrome c oxydase lié à une mutation homozygote du gène SURF1.

Leigh syndrome is a heterogeneous disorder, usually due to a defect in oxidative metabolism. Mutations in SURF1 gene have been identified in patients with cytochrome c oxidase deficiency. We report a homozygous splice site deletion [516-2_516-1delAG] in a young girl presenting with cytochrome c oxidase-deficient Leigh syndrome. Identification of molecular defect is indispensable for genetic counselling and prenatal diagnosis.

Phenotypic expression of diabetes secondary to a T14709C mutation of mitochondrial DNA. Comparison with MIDD syndrome (A3243G mutation): a case report.

OBJECTIVE: To analyze the clinical and biochemical features of a recently described point mutation of mitochondrial DNA associated with diabetes. This mutation, characterized by a T14709C transition of a highly conserved nucleotide in the region coding for the glutamic acid tRNA, is heteroplasmic. RESEARCH DESIGN AND METHODS: The phenotypic expression in the insulin-requiring diabetic proband from the pedigree was compared to that of diabetic probands from three families with the classic A3243G mtDNA mutation (maternally inherited diabetes and deafness [MIDD] syndrome). The same investigations to evaluate pancreatic neurosensorial and muscle involvement were performed in all four patients. RESULTS: The natural courses of the diabetes and the hearing defects were not different between the two mutations. The patient with the 14,709 mutation, however, exhibited a milder alteration of pigmentary epithelium of retina and a much more severe muscle involvement, as attested by the clinical expression and the concurrent anomalies of muscle energy production evidenced by 31P magnetic resonance spectroscopy, confirming the profound impairment of oxidative processes. CONCLUSIONS: This novel mutation has to be added to the other known mtDNA anomalies in order to ascribe some diabetes suspected to arise from mitochondrial defects to this nosological framework.

Importance of searching for associated mitochondrial DNA alterations in patients with multiple deletions.

Multiple mitochondrial DNA (mtDNA) deletions have been reported in patients with autosomal dominant and recessive disorders. We studied several affected and one non-affected individuals belonging to a pedigree in which the inheritance of the pathological trait was compatible with an autosomique dominant transmission. Affected members had late-onset multisystem disorders with multiple mtDNA deletions in skeletal muscle. But this family presented a striking difference from previously described cases, because none of the patients had progressive external ophthalmoplegia (PEO). We also studied one young boy with a no contributary family history. He had a cerebellar ataxia with PEO and multiple mtDNA deletions in muscle. Molecular analysis revealed that in the first family, repeated sequences were present at the breakpoint junctions, whereas such motifs were not found in the young patient's case. In the first family, we evidenced mtDNA point mutations in clones containing breakpoint junctions and a 9-bp motif triplication in the intergenic COII/tRNA(Lys) region, whereas this sequence is repeated twice in the wild type mtDNA. Our results suggest that multiple deletions observed in the two pedigrees result from different molecular mechanisms and point out the role of repeated sequences in the first pedigree. No mtDNA repair system has been described in mammals so far, but the molecular abnormalities found in the first family suggest that a defect in an mtDNA repair system, homologous to the E. coli MutHLS pathway, could be responsible for such a phenotype.

Clinical aspects of mitochondrial diabetes.

Mitochondrial diabetes is a new nosological entity, the most common form of which is maternally inherited diabetes and deafness (MIDD) syndrome. In this syndrome, delayed insulin dependency is frequently observed, although any form of glucose intolerance is possible. The mechanism of diabetes is localised at the beta-cell level. The participation of an autoimmune process in beta-cell loss is still controversial. An association with macular pattern dystrophy and infraclinical myopathy is common and can facilitate diagnosis. Muscle 31-P MR spectroscopy is a non-invasive tool to detect oxidative and phosphorylative alterations and monitor the reversion of these anomalies through specific treatments. Numerous other mutations, deletions or duplications of mtDNA have been associated with diabetes. The description of mitochondrial diabetes is still in progress. In future, an understanding of the mechanism of glucose intolerance in these diseases should open the way to specific preventive treatments in subjects carrying diabetogeneic mutations of mtDNA.

Heterogeneity of diabetes phenotype in patients with 3243 bp mutation of mitochondrial DNA (Maternally Inherited Diabetes and Deafness or MIDD).

OBJECTIVE: In patients with maternally inherited diabetes and deafness (MIDD), due to 3 243 A > G mutation of mitochondrial DNA (mtDNA), diabetes may present with variable phenotypes. OBJECTIVE: To ascertain the existence of two distinct phenotypes, MIDD1 and MIDD2, in a series of patients with MIDD. DESIGN: Multicenter prospective study. PATIENTS: 77 patients with diabetes and the mtDNA 3243 mutation and 139 control patients with type 1 (T1D) or type 2 (T2D) diabetes, matched according to initial presentation of diabetes, age at onset, sex, and duration of diabetes (24 T1D and 115 T2D, including 55 treated with insulin). MEASUREMENTS: Anthropometric characteristics (height, body weight, body mass index [BMI], sex), family history of diabetes, and characteristics of diabetes (age at onset, treatment, hemoglobin A1c [HbA1c]), extrapancreatic manifestations. RESULTS: In 13 cases (17%, MIDD1), diabetes presented as insulin-dependent from the onset, with ketoacidosis in 6 cases. In 64 cases (83%, MIDD2), diabetes resembled T2D, and was treated with diet in 12 cases, oral hypoglycemic agents in 21 cases, or insulin in 31 cases. Compared with patients with MIDD2, patients with MIDD1 were characterized by lower age at onset of first manifestation of MIDD (25.4 +/- 9.6 vs 33.7 +/- 13.2 Years, P<0.0005), lower body weight (49.1 +/- 7.4 vs 56.3 +/- 10.9 kg, P<0.0025), lower BMI (18.2 +/- 2.3 vs 20.9 +/- 3.6 kg/m2, P<0.0005), and higher HbA1c levels (9.5 +/- 2.0 vs 7.5 +/- 1.6%, P<0.0005). Frequency of family history of diabetes and of extrapancreatic manifestations was the same in both MIDD subtypes. No difference was found within the MIDD2 subtype when comparing patients treated with or without insulin. Compared with matched controls, patients with MIDD had a lower BMI (MIDD1/T1D 18.2 +/- 2.3 vs 24.0 +/- 3.6 kg/m2 and MIDD2/T2D 20.9 +/- 3.6 vs 30.2 +/- 5.9 kg/m2, P<0.0025). Lastly, male patients with MIDD had a shorter height than controls (MIDD1/T1D: 166.1 +/- 3.2 vs 177.3 +/- 6.6 cm and MIDD2/T2D: 168.4 +/- 7.2 vs 173.6 +/- 6.6 cm P<0.025). CONCLUSIONS: These results confirm the existence of two different phenotypes in MIDD, MIDD1 and MIDD2, which may be related to the severity of the mitochondrial disease. The role of other genetic and/or environmental factors in the variable phenotype of MIDD remains to be elucidated.

[Epilepsy and mitochondrial diseases: retrospective study on 53 epileptic children]. / Épilepsie et cytopathies mitochondriales : étude rétrospective de 53 enfants épileptiques.

AIM: Mitochondrial disease is a heterogeneous disorder entity induced by defects in the mitochondrial respiratory chain complex. Neurological symptoms, including epilepsy, are common in children. The aim of this study was to research the clinical signs indicating mitochondrial disease. METHODS: We retrospectively studied epileptic children who underwent a muscle and/or hepatic biopsy between 1995 and 2010 searching for a mitochondrial disease. Patients were separated into 2 groups depending on the biopsy result: group 1 (presence of mitochondrial disease) and group 2 (absence of mitochondrial disease). Epileptic phenotypes were compared between these 2 groups. In group 1, we specified the clinical phenotype and characterized mitochondrial disease. RESULTS: Fifty-three children were included: 29 in group 1 and 24 in group 2. The average age at onset of epilepsy was 39.6 months in group 1 versus 11.8 months in group 2. In the 1st group, epilepsy was less refractory and associated with other clinical symptoms. CONCLUSIONS: In this study, epilepsy did not appear to be a unique sign of mitochondrial disease. It most often appeared during the 2nd year of life and is correlated with multiorgan involvement, notably ophthalmologic, such as oculomotor apraxia, optic atrophy, and retinitis pigmentosa, as well as auditory (deafness) and hepatic (hepatic failure, hepatomegaly). On the other hand, in children who did not have mitochondrial disease, epilepsy often began earlier (before 3 months of age), it was refractory, isolated without multiorgan involvement, and seems to be due to genetic anomalies in developmental genes, a finding that requires further research.

Fatal case of Reye's syndrome associated with H3N2 influenza virus infection and salicylate intake in a 12-year-old patient.

We describe a fatal case of Reye's syndrome in a 12-year-old male patient during an influenza A (H3N2) infection for which he received salicylates. In the current situation of the novel A/H1N1 virus pandemic, we believe that it is of high importance to emphasize the risks associated with salicylate intake to avoid the reappearance of Reye's syndrome.