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.

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.

[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.

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.

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.

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.

Brain anomalies in maternally inherited diabetes and deafness syndrome.

Maternally inherited diabetes and deafness (MIDD) and myoencephalopathy, lactic acidosis, stroke-like episodes (MELAS) syndromes are characterized by the same A3243G mutation of mitochondrial DNA (mtDNA). Should there be a link between these two clinical entities, one could expect to observe minor signs of MELAS in MIDD patients. To examine this issue, extensive evaluations of brain function and imaging in patients with mitochondrial diabetes and in age-matched type 1 diabetic patients were conducted and compared. MIDD patients (nine A3243G, two T14709G) and nine age-matched type 1 diabetic patients (T1D) were submitted for evaluation of cognitive functions, brain magnetic resonance (MR) imaging, and 1H-MR spectroscopy. Three MIDD patients exhibited cerebellar ataxia. The MIDD group exhibited poorer performances in sustained attention, verbal memory working, and abstract reasoning procedures, in comparison with the T1D group. MR imaging showed cerebellar atrophy in seven out of ten MIDD patients (versus 3 mild/8 in T1D controls) and basal ganglia calcifications in one MIDD patient. No evidence of (sub)acute stroke was detected. White-matter anomalies were observed in both groups (50%). 1H-MR spectroscopy revealed a significant decrease of N-acetyl aspartate only in vermis in the MIDD group, suggesting functional defect and/or neuronal loss. Lactate was detected in cerebrospinal fluid (CSF) in two MIDD and one T1D patient. Typical manifestations of MELAS are rare in MIDD syndrome, suggesting two different clinical entities. However, cerebellum involvement as assessed by imaging and 1H-MR spectroscopy is shared by both phenotypes.

The clinical variability of maternally inherited diabetes and deafness is associated with the degree of heteroplasmy in blood leukocytes.

CONTEXT: Maternally inherited diabetes and deafness (MIDD) is a rare form of diabetes with a matrilineal transmission, sensorineural hearing loss, and macular pattern dystrophy due to an A to G transition at position 3243 of mitochondrial DNA (mtDNA) (m.3243A>G). The phenotypic heterogeneity of MIDD may be the consequence of different levels of mutated mtDNA among mitochondria in a given tissue. OBJECTIVE: The aim of the present study was thus to ascertain the correlation between the severity of the phenotype in patients with MIDD and the level of heteroplasmy in the blood leukocytes. PARTICIPANTS: The GEDIAM prospective multicenter register was initiated in 1995. Eighty-nine Europid patients from this register, with MIDD and the mtDNA 3243A>G mutation, were included. Patients with MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) or with mitochondrial diabetes related to other mutations or to deletions of mtDNA were excluded. RESULTS: A significant negative correlation was found between levels of heteroplasmy and age of the patients at the time of sampling for molecular analysis, age at the diagnosis of diabetes, and body mass index. After adjustment for age at sampling for molecular study and gender, the correlation between heteroplasmy levels and age at the diagnosis of diabetes was no more significant. The two other correlations remained significant. A significant positive correlation between levels of heteroplasmy and HbA(1c) was also found and remained significant after adjustment for age at molecular sampling and gender. CONCLUSIONS: These results support the hypothesis that heteroplasmy levels are at least one of the determinants of the severity of the phenotype in MIDD.

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.

Retinal and renal complications in patients with a mutation of mitochondrial DNA at position 3,243 (maternally inherited diabetes and deafness). A case-control study.

AIMS/HYPOTHESIS: We assessed the prevalence and determinants of retinal and renal complications in patients with maternally inherited diabetes and deafness (MIDD). METHODS: This was a multicentre prospective study comparing the prevalence of retinopathy and renal disease in 74 patients with MIDD and 134 control patients matched for sex, age and clinical presentation at onset of diabetes, duration of diabetes and current treatment. Comparisons were adjusted for HbA(1c) and hypertension. RESULTS: In MIDD patients, HbA(1c) (7.6 +/- 1.6 vs 8.5 +/- 2.0%, p < 0.002), systolic blood pressure (126.6 +/- 16.2 vs 133.1 +/- 17.3 mmHg, p < 0.007) and prevalence of hypertension (33.8 vs 64.2%, p < 0.0001) were lower than in control patients. Prevalence of diabetic retinopathy was 3.7-fold lower in MIDD patients (6/74, 8 vs 40/134, 29.6%, p < 0.0001). Differences between groups remained significant after adjustment for hypertension, systolic blood pressure and HbA(1c). In MIDD, urinary albumin excretion (314.8 vs 80.1 mg/24 h, p = 0.035) and creatinine plasma levels (103.5 vs 82.2 micromol/l, p = 0.0178) were higher and GFR was lower. Impaired renal function (GFR <60 ml/min) was four- to sixfold more frequent in MIDD. Differences between MIDD and control diabetic patients further increased when adjusted for HbA(1c) and systolic blood pressure (p < 0.0001). Adjustment for treatment with an ACE inhibitor or angiotensin II receptor antagonist did not modify the results. CONCLUSIONS/INTERPRETATION: This study indicates that diabetic retinopathy is less prevalent in MIDD than in control diabetes. This suggests that retinal alterations due to mitochondrial disease may have a protective role. By contrast, nephropathy is far more frequent in MIDD, suggesting the presence of a specific renal disease independent of diabetic nephropathy.

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).

Identification of novel mutations in WFS1 and genotype-phenotype correlation in Wolfram syndrome.

Mutations in the WFS1 gene have been reported in Wolfram syndrome (WS), an autosomal recessive disorder defined by early onset of diabetes mellitus (DM) and progressive optic atrophy. Because of the low prevalence of this syndrome and the recent identification of the WFS1 gene, few data are available concerning the relationships between clinical and molecular aspects of the disease. Here, we describe 12 patients from 11 families with WS. We report on eight novel (A214fsX285, L293fsX303, P346L, I427S, V503fsX517, R558C, S605fsX711, P838L) and seven previously reported mutations. We also looked for genotype-phenotype correlation both in patients included in this study and 19 additional WS patients that were previously reported. Subsequently, we performed a systematic review and meta-analysis of five published clinical and molecular studies of WFS1 for genotype-phenotype correlation, combined with our current French patient group for a total of 96 patients. The presence of two inactivating mutations was shown to predispose to an earlier age of onset of both DM and optic atrophy. Moreover, the clinical expression of WS was more complete and occurred earlier in patients harboring no missense mutation.

A novel homozygous MMP2 mutation in a family with Winchester syndrome.

The 2001 International Classification of Constitutional Disorders of Bone has included in the group of multicentric hands and feet osteolysis syndromes three autosomal recessive inherited disorders: Winchester, Torg and nodulosis-arthropathy-osteolysis (NAO) syndromes. Nosographic delineations of these rare syndromes are difficult to define, and there is no consensus. In 2001, two mutations in the matrix metalloproteinase 2 gene (MMP2) have been identified in two families with a NAO phenotype. In a recent study, a homozygous MMP2 mutation has also been identified in a patient presenting with Winchester syndrome. We report the clinical evolution of two sisters with a Winchester phenotype. Clinical review over 23 years provides information on the general evolution of osteolysis and points to an intrafamilial variation with clinical and radiological changes during the patients' life. In both sisters, we identified a new homozygous mutation in the catalytic domain of the MMP2 gene. Our study results are consistent with the involvement of MMP2 in Winchester syndrome and with the hypothesis that Winchester and NAO syndromes are allelic disorders that form a continuous clinical spectrum. At last, our observation emphasizes the interest of molecular analysis in genetic counselling of this consanguineous family.

[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.

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.