👤 Gautham Arunachal

Congenital myasthenic syndromes (CMS) are a rare group of inherited disorders caused by gene defects associated with the neuromuscular junction and potentially treatable with commonly available medications such as acetylcholinesterase inhibitors and β2 adrenergic receptor agonists. In this study, we identified and genetically characterized the largest cohort of CMS patients from India to date. Genetic testing of clinically suspected patients evaluated in a South Indian hospital during the period 2014-19 was carried out by standard diagnostic gene panel testing or using a two-step method that included hotspot screening followed by whole-exome sequencing. In total, 156 genetically diagnosed patients (141 families) were characterized and the mutational spectrum and genotype-phenotype correlation described. Overall, 87 males and 69 females were evaluated, with the age of onset ranging from congenital to fourth decade (mean 6.6 ± 9.8 years). The mean age at diagnosis was 19 ± 12.8 (1-56 years), with a mean diagnostic delay of 12.5 ± 9.9 (0-49 years). Disease-causing variants in 17 CMS-associated genes were identified in 132 families (93.6%), while in nine families (6.4%), variants in genes not associated with CMS were found. Overall, postsynaptic defects were most common (62.4%), followed by glycosylation defects (21.3%), synaptic basal lamina genes (4.3%) and presynaptic defects (2.8%). Other genes found to cause neuromuscular junction defects (DES, TEFM) in our cohort accounted for 2.8%. Among the individual CMS genes, the most commonly affected gene was CHRNE (39.4%), followed by DOK7 (14.4%), DPAGT1 (9.8%), GFPT1 (7.6%), MUSK (6.1%), GMPPB (5.3%) and COLQ (4.5%). We identified 22 recurrent variants in this study, out of which eight were found to be geographically specific to the Indian subcontinent. Apart from the known common CHRNE variants p.E443Kfs*64 (11.4%) and DOK7 p.A378Sfs*30 (9.3%), we identified seven novel recurrent variants specific to this cohort, including DPAGT1 p.T380I and DES c.1023+5G>A, for which founder haplotypes are suspected. This study highlights the geographic differences in the frequencies of various causative CMS genes and underlines the increasing significance of glycosylation genes (DPAGT1, GFPT1 and GMPPB) as a cause of neuromuscular junction defects. Myopathy and muscular dystrophy genes such as GMPPB and DES, presenting as gradually progressive limb girdle CMS, expand the phenotypic spectrum. The novel genes MACF1 and TEFM identified in this cohort add to the expanding list of genes with new mechanisms causing neuromuscular junction defects. Show less

Genetic cardiomyopathies (CM) are disorders that affect morphology and function of cardiac muscle. Significant number of genes have been implicated in causing the phenotype. It is one of the leading genetic causes of death in young. We performed a study to understand the genetic variants in primary cardiomyopathies in an Indian cohort. Study comprised of 22 probands (13 with family history) representing hypertrophic (n = 10), dilated (n = 7), restrictive (n = 2) and arrhythmogenic ventricular(n = 3) cardiomyopathies. Genomic DNA was target captured with a panel of 46 genes and libraries sequenced on Illumina platform. Analysis identified, reported pathogenic as well as novel pathogenic (n = 6) variants in 16 probands. Of the 10 HCM patients, candidate variants were identified in nine of them involving sarcomere genes (62%, MYBPC3, MYH6, MYH7, MYL3, TTN), Z-disc (10%, ACTN2, LDB3, NEXN,), desmosome (10%, DSG2, DSP, PKP2) cytoskeletal (4%, DTNA) and ion channel (10% RYR2). In four DCM patients, variants were identified in genes NEXN, LMNA and TTN. Three arrhythmogenic right ventricular cardiomyopathy (ARVD) patients carried mutations in desmosome genes. Rare TTN variants were identified in multiple patients. Targeted capture and sequencing resulted in identification of candidate variants in about 70% of the samples which will help in management of disease in affected individual as well as in screening and early diagnosis in asymptomatic family members. Amongst the analysed cases, 22% were inconclusive without any significant variant identified. Study illustrates the utility of next-generation multi-gene panel as a cost-effective genetic testing to screen all forms of primary cardiomyopathies. Show less

To investigate the mutational spectrum and genotype-phenotype correlation in Indian patients with congenital myasthenic syndrome (CMS), using next-generation sequencing of 5 genes. CHRNE, COLQ, DOK7, RAPSN, and GFPT1 were sequenced in 25 affected patients. We found clinically significant variants in 18 patients, of which variants in CHRNE were the most common, and 9 were novel. A common pathogenic COLQ variant was also detected in 4 patients with isolated limb-girdle congenital myasthenia. Targeted screening of 5 genes is an effective alternate test for CMS, and an affordable one even in a developing country such as India. In addition, we recommend that patients with isolated limb-girdle congenital myasthenia be screened initially for the common COLQ pathogenic variant. This study throws the first light on the genetic landscape of CMSs in India. Show less