The new missense G376V-TDP-43 variant induces late-onset distal myopathy but not amyotrophic lateral sclerosis.

TDP-43-positive inclusions in neurons are a hallmark of several neurodegenerative diseases including familial amyotrophic lateral sclerosis (fALS) caused by pathogenic TARDBP variants as well as more common non-Mendelian sporadic ALS (sALS). Here we report a G376V-TDP-43 missense variant in the C-terminal prion-like domain of the protein in two French families affected by an autosomal dominant myopathy but not fulfilling diagnostic criteria for ALS. Patients from both families presented with progressive weakness and atrophy of distal muscles, starting in their 5th-7th decade. Muscle biopsies revealed a degenerative myopathy characterized by accumulation of rimmed (autophagic) vacuoles, disruption of sarcomere integrity and severe myofibrillar disorganization. The G376 V variant altered a highly conserved amino acid residue and was absent in databases on human genome variation. Variant pathogenicity was supported by in silico analyses and functional studies. The G376 V mutant increased the formation of cytoplasmic TDP-43 condensates in cell culture models, promoted assembly into high molecular weight oligomers and aggregates in vitro, and altered morphology of TDP-43 condensates arising from phase separation. Moreover, the variant led to the formation of cytoplasmic TDP-43 condensates in patient-derived myoblasts and induced abnormal mRNA splicing in patient muscle tissue. The identification of individuals with TDP-43-related myopathy but not ALS implies that TARDBP missense variants may have more pleiotropic effects than previously anticipated and support a primary role for TDP-43 in skeletal muscle pathophysiology. We propose to include TARDBP screening in the genetic work-up of patients with late-onset distal myopathy. Further research is warranted to examine the precise pathogenic mechanisms of TARDBP variants causing either a neurodegenerative or myopathic phenotype.

Muscular phenotype description of abnormal THOC2 splicing.

Until recently, the disease known to be associated with THOC2 mutations was Intellectual developmental disorder, X-linked 12 (MIM300957). However, recently, fetal arthrogryposis multiplex congenita has been associated with a specific splice site mutation in the THOC2 gene. We report a family with the same splice site mutation in the THOC2 gene involved in fetal arthrogryposis as well. We provide the first description of the muscular phenotype of this disease which reveals the presence of cytoplasmic bodies. Our findings expand the clinical phenotype of THOC2 gene related defects.

Immune-Mediated Rippling Muscle Disease Associated With Thymoma and Anti-MURC/Cavin-4 Autoantibodies.

OBJECTIVES: Rippling muscle disease (RMD) is characterized by muscle stiffness, muscle hypertrophy, and rippling muscle induced by stretching or percussion. Hereditary RMD is due to sequence variants in the CAV3 and PTRF/CAVIN1 genes encoding Caveolin-3 or Cavin-1, respectively; a few series of patients with acquired autoimmune forms of RMD (iRMD) associated with AChR antibody-positive myasthenia gravis and/or thymoma have also been described. Recently, MURC/caveolae-associated protein 4 (Cavin-4) autoantibody was identified in 8 of 10 patients without thymoma, highlighting its potential both as a biomarker and as a triggering agent of this pathology. Here, we report the case of a patient with iRMD-AchR antibody negative associated with thymoma. METHODS: We suspected a paraneoplastic origin and investigated the presence of specific autoantibodies targeting muscle antigens through a combination of Western blotting and affinity purification coupled with mass spectrometry-based proteomic approaches. RESULTS: We identified circulating MURC/Cavin-4 autoantibodies and found strong similarities between histologic features of the patient's muscle and those commonly reported in caveolinopathies. Strikingly, MURC/Cavin-4 autoantibody titer strongly decreased after tumor resection and immunotherapy correlating with complete disappearance of the rippling phenotype and full patient remission. DISCUSSION: MURC/Cavin-4 autoantibodies may play a pathogenic role in paraneoplastic iRMD associated with thymoma.

Mild limb girdle muscular dystrophy R9 phenotype caused by novel compound heterozygous FKRP gene mutation.

Fukutin-related protein (FKRP) mutations cause a broad spectrum of muscular dystrophies, from a relatively mild limb-girdle muscular dystrophy type 9 (LGMDR9) to severe congenital muscular dystrophy (CMD). This study aims to report two siblings belonging to a non-consanguineous Tunisian family harboring a novel compound heterozygous FKRP variant and presenting a mild LGDMR9 phenotype. For mutation screening, massive parallel sequencing was performed, followed by Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA) to validate the existence of the discovered variants. The absence of alpha-dystroglycan was determined by immunohistochemistry. Brain and thigh magnetic resonance imaging (MRI) were performed to detect thigh and brain abnormalities. The two siblings had a late age at onset and clinical examination showed that the pelvic girdles had a predominantly proximal and symmetrical distribution of weakness without cardiac or respiratory involvement. They both had a modified Gardner-Medwin Walton Scale mGMWS grade of 4 and a modified Rankin Scale (mRS) score of 1. The DNA sequencing revealed a novel deletion of exons 2 and 3 in one allele and a missense mutation c.1364C > A, which has been reported to be responsible for congenital muscular dystrophy and mental retardation on the second allele. The simultaneous presence of the two variations in the two cases suggests that the variants segregate with the pathophysiology.

Novel Intronic Mutation in VMA21 Causing Severe Phenotype of X-Linked Myopathy with Excessive Autophagy-Case Report.

X-linked Myopathy with Excessive Autophagy (XMEA) is a rare autophagic vacuolar myopathy caused by mutations in the Vacuolar ATPase assembly factor VMA21 gene; onset usually occurs during childhood and rarely occurs during adulthood. We described a 22-year-old patient with XMEA, whose onset was declared at 11 through gait disorder. He had severe four-limb proximal weakness and amyotrophy, and his proximal muscle MRC score was between 2 and 3/5 in four limbs; creatine kinase levels were elevated (1385 IU/L), and electroneuromyography and muscle MRI were suggestive of myopathy. Muscle biopsy showed abnormalities typical of autophagic vacuolar myopathy. We detected a hemizygous, unreported, intronic, single-nucleotide substitution c.164-20T>A (NM_001017980.4) in intron 2 of the VMA21 gene. Fibroblasts derived from this patient displayed a reduced level of VMA21 transcripts (at 40% of normal) and protein, suggesting a pathogenicity related to an alteration of the splicing efficiency associated with an intron retention. This patient with XMEA displayed a severe phenotype (rapid weakness of upper and lower limbs) due to a new intronic variant of VMA21, related to an alteration in the splicing efficiency associated with intron retention, suggesting that phenotype severity is closely related to the residual expression of the VMA21 protein.

Prenatal dexamethasone treatment for classic 21-hydroxylase deficiency in Europe.

Objective: To assess the current medical practice in Europe regarding prenatal dexamethasone (Pdex) treatment of congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency. Design and methods: A questionnaire was designed and distributed, including 17 questions collecting quantitative and qualitative data. Thirty-six medical centres from 14 European countries responded and 30 out of 36 centres were reference centres of the European Reference Network on Rare Endocrine Conditions, EndoERN. Results: Pdex treatment is currently provided by 36% of the surveyed centres. The treatment is initiated by different specialties, that is paediatricians, endocrinologists, gynaecologists or geneticists. Regarding the starting point of Pdex, 23% stated to initiate therapy at 4-5 weeks postconception (wpc), 31% at 6 wpc and 46 % as early as pregnancy is confirmed and before 7 wpc at the latest. A dose of 20 µg/kg/day is used. Dose distribution among the centres varies from once to thrice daily. Prenatal diagnostics for treated cases are conducted in 72% of the responding centres. Cases treated per country and year vary between 0.5 and 8.25. Registries for long-term follow-up are only available at 46% of the centres that are using Pdex treatment. National registries are only available in Sweden and France. Conclusions: This study reveals a high international variability and discrepancy in the use of Pdex treatment across Europe. It highlights the importance of a European cooperation initiative for a joint international prospective trial to establish evidence-based guidelines on prenatal diagnostics, treatment and follow-up of pregnancies at risk for CAH.

Clinical and Molecular Spectrum Associated with COL6A3 c.7447A>G p.(Lys2483Glu) Variant: Elucidating its Role in Collagen VI-related Myopathies.

BACKGROUND: Dominant and recessive autosomal pathogenic variants in the three major genes (COL6A1-A2-A3) encoding the extracellular matrix protein collagen VI underlie a group of myopathies ranging from early-onset severe conditions (Ullrich congenital muscular dystrophy) to milder forms maintaining independent ambulation (Bethlem myopathy). Diagnosis is based on the combination of clinical presentation, muscle MRI, muscle biopsy, analysis of collagen VI secretion, and COL6A1-A2-A3 genetic analysis, the interpretation of which can be challenging. OBJECTIVE: To refine the phenotypical spectrum associated with the frequent COL6A3 missense variant c.7447A>G (p.Lys2483Glu). METHODS: We report the clinical and molecular findings in 16 patients: 12 patients carrying this variant in compound heterozygosity with another COL6A3 variant, and four homozygous patients. RESULTS: Patients carrying this variant in compound heterozygosity with a truncating COL6A3 variant exhibit a phenotype consistent with COL6-related myopathies (COL6-RM), with joint contractures, proximal weakness and skin abnormalities. All remain ambulant in adulthood and only three have mild respiratory involvement. Most show typical muscle MRI findings. In five patients, reduced collagen VI secretion was observed in skin fibroblasts cultures. All tested parents were unaffected heterozygous carriers. Conversely, two out of four homozygous patients did not present with the classical COL6-RM clinical and imaging findings. Collagen VI immunolabelling on cultured fibroblasts revealed rather normal secretion in one and reduced secretion in another. Muscle biopsy from one homozygous patient showed myofibrillar disorganization and rimmed vacuoles. CONCLUSIONS: In light of our results, we postulate that the COL6A3 variant c.7447A>G may act as a modulator of the clinical phenotype. Thus, in patients with a typical COL6-RM phenotype, a second variant must be thoroughly searched for, while for patients with atypical phenotypes further investigations should be conducted to exclude alternative causes. This works expands the clinical and molecular spectrum of COLVI-related myopathies.

Aberrant Splicing Is the Pathogenicity Mechanism of the p.Glu314Lys Variant in CYP11A1 Gene.

Context: The cholesterol side chain cleavage enzyme (CYP11A1) catalyzes the conversion of cholesterol to pregnenolone, the first rate-limiting step of steroidogenesis. CYP11A1 mutations are associated with primary adrenal insufficiency (PAI) as well as disorders of sex development (DSD) in 46,XY patients. Objective: To define the pathogenicity mechanism for the p.Glu314Lys variant, previously reported, and found in four additional patients with CYP11A1 deficiency. Subjects and Methods: DNA of four patients presenting with delayed PAI and/or 46,XY DSD were studied by Sanger or Massively Parallel sequencing. Three CYP11A1 mutations were characterized in vitro and in silico, and one by mRNA analysis on testicular tissue. Results: All patients were compound heterozygous for the previously described p.Glu314Lys variant. In silico studies predicted this mutation as benign with no effect on splicing but mRNA analysis found that it led to incomplete exon 5 skipping. This mechanism was confirmed by minigene experiment. The protein carrying this mutation without exon skipping should conserve almost normal activity, according to in vitro studies. Two other mutations found in trans, the p.Arg120Gln and p.Arg465Trp, had similar activity compared to negative control, consistent with the in silico studies. Conclusions: We provide biological proof that the p. Glu314Lys variant is pathogenic due to its impact on splicing and seems responsible for the moderate phenotype of the four patients reported herein. The present study highlights the importance of considering the potential effect of a missense variant on splicing when it is not predicted to be disease causing.

News about the genetics of congenital primary adrenal insufficiency.

Primary adrenal insufficiency (PAI) is characterized by impaired production of steroid hormones due to an adrenal cortex defect. This condition incurs a risk of acute insufficiency which may be life-threatening. Today, 80% of pediatric forms of PAI have a genetic origin but 5% have no clear genetic support. Recently discovered mutations in genes relating to oxidative stress have opened the way to research on genes unrelated to the adrenal gland. Identification of causal mutations in a gene responsible for PAI allows genetic counseling, guidance of follow-up and prevention of complications. This is particularly true for stress oxidative anomalies, as extra-adrenal manifestations may occur due to the sensitivity to oxidative stress of other organs such as the heart, thyroid, liver, kidney and pancreas.

A splicing mutation in the DMD gene detected by next-generation sequencing and confirmed by mRNA and protein analysis.

BACKGROUND: Dystrophinopathies, either the severe Duchenne Muscular Dystrophy (DMD) or the milder Becker Muscular Dystrophy (BMD), are X-linked recessive disorders caused by mutations in the DMD gene. DMD is one of the longest human genes. Large deletions or duplications account for 60-80% of the mutations. Remaining anomalies consist in point mutations or small rearrangements. Routinely, the molecular diagnosis is done by a Multiplex Ligation-dependent Probe Amplification (MLPA) or array Comparative Genome Hybridization (aCGH), followed, if negative, by Sanger sequencing of all exons. METHODS: In this study, massive parallel sequencing (MPS) or next generation sequencing (NGS) was used to make a rapid and costless molecular diagnosis in a young boy suspected of DMD. RESULTS: A small deletion: NM_004006.2:c.2803+5_2803+8del was identified. The diagnosis was performed in one single manipulation and within a week. The consequence of this intronic mutation is a skipping of exon 21 confirmed by mRNA and protein analysis. CONCLUSIONS: NGS appears to be an efficient new strategy in DMD molecular diagnosis. It highlights the major evolution of the diagnostic strategy towards high throughput technologies, where bioinformatics analysis becomes the real challenge for variations detection. This is the first study reporting in vivo impact of this intronic mutation.

Functional variants of POC5 identified in patients with idiopathic scoliosis.

Idiopathic scoliosis (IS) is a spine deformity that affects approximately 3% of the population. The underlying causes of IS are not well understood, although there is clear evidence that there is a genetic component to the disease. Genetic mapping studies suggest high genetic heterogeneity, but no IS disease-causing gene has yet been identified. Here, genetic linkage analyses combined with exome sequencing identified a rare missense variant (p.A446T) in the centriolar protein gene POC5 that cosegregated with the disease in a large family with multiple members affected with IS. Subsequently, the p.A446T variant was found in an additional set of families with IS and in an additional 3 cases of IS. Moreover, POC5 variant p.A455P was present and linked to IS in one family and another rare POC5 variant (p.A429V) was identified in an additional 5 cases of IS. In a zebrafish model, expression of any of the 3 human IS-associated POC5 variant mRNAs resulted in spine deformity, without affecting other skeletal structures. Together, these findings indicate that mutations in the POC5 gene contribute to the occurrence of IS.

New management strategy of pregnancies at risk of congenital adrenal hyperplasia using fetal sex determination in maternal serum: French cohort of 258 cases (2002-2011).

CONTEXT: Prenatal dexamethasone (DEX) treatment has been proposed since 1984 to prevent genital virilization in girls with congenital adrenal hyperplasia (CAH). DEX is effective in CAH females if initiated before the sixth week of gestation, but its safety in children treated in utero remains controversial regarding cognitive functions. OBJECTIVE: To avoid prenatal DEX in males and initiate DEX in due time in CAH females, we proposed in 2002 a protocol for fetal sex determination in the maternal serum (SRY test). DESIGN AND SETTING: We conducted a retrospective study of the management of 258 fetuses in the period 2002 through 2011 in pregnancies managed in referent medical centers with an institutional practice. PATIENTS: A total of 258 fetuses at risk of CAH (134 males and 124 females) were included. INTERVENTION: DEX was offered after informed consent to pregnant women. MAIN OUTCOME MEASURE: The sensitivity of an early SRY test was evaluated after data collection. RESULTS: The SRY test is sensitive from 4 weeks and 5 days of gestation. It avoided prenatal DEX in 68% of males, and this percentage increased over the years. DEX was maintained until prenatal diagnosis in non-CAH females. Virilization was prevented in 12 CAH girls treated at the latest at 6 weeks gestation and minimized in 3 girls treated between 6 and 7 weeks gestation. Maternal tolerance was correct. No fetal malformations were noted in the 154 children treated in utero. CONCLUSIONS: The SRY test is reliable to avoid prenatal DEX in males, but its application must be improved. Prenatal DEX should be maintained to prevent virilization and traumatic surgery in CAH girls after informed consent and information provided to families about the benefit to risk ratio in limiting hyperandrogenism during fetal life. Our large multicentric French cohort has helped to better assess the risks previously reported.

Mutational spectrum of cystic fibrosis in the Lebanese population.

BACKGROUND: Cystic fibrosis (CF) is the most common autosomal recessive disease in Caucasians; it is however, considered to be rare in the Arab populations. Reports of the cystic fibrosis transmembrane regulator (CFTR) mutations from Arabs, especially from the Lebanese population, are limited. METHODS: Twenty-two unrelated Lebanese families, with at least one child with CF, were studied. DNA extracts from blood samples of patients and parents were screened for CFTR gene mutations. RESULTS: Eleven different mutations were identified. Of the 44 alleles studied, the most common mutations were: F508del (34%), N1303K (27%), W1282X (7%), and S4X (7%). Five mutations - not previously reported in the Lebanese population - were identified; these are: S549N, G542X, 2043delG, 4016insG, and R117H-7T. CONCLUSIONS: The most common CFTR mutations in addition to five mutations not previously described in the Lebanese population were identified. Identification of CFTR mutations in the Lebanese population is important for molecular investigations and genetic counseling.