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To our knowledge, this is the first comprehensive mutational analyses in congenital muscular dystrophy (CMD) and congenital myopathy (CM) patients from India. Importantly, these findings allowed us to achieve accurate genetic diagnosis of CMD (n = 12/22, 54%) and CM (n = 5/14, 34%) cases, which was difficult using conventional diagnostic tools. Transferring these whole‐exome sequencing analyses findings to clinical practice will help guide clinical care of the affected patients and inform genetic counselling.

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The sarcoglycanopathies are autosomal recessive limb-girdle muscular dystrophies (LGMDs) caused by the mutations in genes encoding the α, β, γ, and δ proteins which stabilizes the sarcolemma of muscle cells. The clinical phenotype is characterized by progressive proximal muscle weakness with childhood onset. Muscle biopsy findings are diagnostic in confirming dystrophic changes and deficiency of one or more sarcoglycan proteins. In this study, we summarized 1,046 LGMD patients for which a precise diagnosis was identified using targeted sequencing. The most frequent phenotypes identified in the patients are LGMDR1 (19.7%), LGMDR4 (19.0%), LGMDR2 (17.5%), and MMD1 (14.5%). Among the reported genes, each of CAPN3, SGCB, and DYSF variants was reported in more than 10% of our study cohort. The most common variant SGCB p.Thr182Pro was identified in 146 (12.5%) of the LGMD patients, and in 97.9% of these patients, the variant was found to be homozygous. To understand the genetic structure of the patients carrying SGCB p.Thr182Pro, we genotyped 68 LGMD patients using a whole genome microarray. Analysis of the array data identified a large ~1 Mb region of homozygosity (ROH) (chr4:51817441-528499552) suggestive of a shared genomic region overlapping the recurrent missense variant and shared across all 68 patients. Haplotype analysis identified 133 marker haplotypes that were present in ~85.3% of the probands as a double allele and absent in all random controls. We also identified 5 markers (rs1910739, rs6852236, rs13122418, rs13353646, and rs6554360) which were present in a significantly higher proportion in the patients compared to random control set ( n = 128 ) and the population database. Of note, admixture analysis was suggestive of greater proportion of West Eurasian/European ancestry as compared to random controls. Haplotype analysis and frequency in the population database indicate a probable event of founder effect. Further systematic study is needed to identify the communities and regions where the SGCB p.Thr182Pro variant is observed in higher proportions. After identifying these communities and//or region, a screening program is needed to identify carriers and provide them counselling.

BackgroundSarcoglycanopathies (SG) is the most frequent form of autosomal recessive limb-girdle muscular dystrophies (LGMD) leading to progressive muscle wasting and weakness, predominantly characterized by limb-girdle weakness. LGMDR4 is caused by mutations in SGCB encoding for the beta-sarcoglycan proteins. In this study, we describe a shared, common haplotype cosegregating in 14 SG cases from 13 unrelated families with the likely pathogenic homozygous mutation c.544A>C (p.Thr182Pro) in SGCB.MethodsThe genotypes of five selected markers (rs10009426, rs6824707, rs2271046, rs35414474 and rs17611952) surrounding the c.544A>C (p.Thr182Pro) were extracted from the variant call format (VCF) generated from whole-exome sequencing (WES) of 14 cases and 14 related family members as controls. The linkage data file was constructed and linkage disequilibrium (LD) plots were generated using HaploView to visualize patterns of LD. Further, haplotype reconstructions based on the 6 markers were conducted using PLINK1.9. using the expectation-maximization (EM) algorithm, an iterative method to find maximum likelihood. Subsequently, the R programming language was used to determine and compare plots of the haplotype frequencies and percentages for both groups to infer the risk haplotypes.ResultsFour strong LD blocks were identified in control group: rs10009426 to rs6824707 (0.27□kb), rs6824707 to rs2271046 (41.6 kb), rs10009426 to rs2271046 (41.8 kb) and rs35414474 to rs17611952 (0.17 kb) which were absent in the case group. Similarly, a total of nine haplotypes were estimated in cases and controls of which haplotype H1= G, A, T, G, G, T showed significant statistical difference in the frequency between cases and controls. H1 is also observed to cosegregate with c.544A>C (p.Thr182Pro) in the pedigrees of all the cases.ConclusionThe identification of c.544A>C (p.Thr182Pro) mutation in 14 cases from India indicates a probable event of founder effect. Further, the H1 haplotype, cosegregating with this mutation, convincingly sheds light on the recent developments in population genetics allowing insights into demographic and population history. This haplotype can also be used as a genetic marker to screen individuals with genetic susceptibility as carriers and provide genetically informed risk stratification and management in the prevention of SG.