The impact of exome sequencing on the diagnostic yield of muscular dystrophies in consanguineous families

Muscular dystrophies (MDs) are a heterogeneous group of inherited disorders that are characterized by progressive skeletal muscle weakness and dystrophic changes on muscle biopsy. The broad genetic and clinical heterogeneity of MDs make the accurate diagnosis difficult via conventional approaches. This study investigated 23 patients from eight unrelated consanguineous families with MDs. Previous clinical assessments did not accurately clarify the type of their MD and/or misdiagnose them with another disease. Exome sequencing (ES) is an efficient, time-saving, and cost-effective tool, enabling disease-causing variant (DCV) detection in affected individuals. We investigated the use of ES to diagnose MD and discover the underlying genetic etiology. We achieved a remarkable diagnostic success rate of 87.5% (7 out of 8 families) which is the highest rate reported thus far compared to previous studies. We identified two novel pathogenic variants in DYSF gene (c.4179delG, c.1149+3G > C). The latter variant impacts the splicing machinery of DYSF mRNA. Moreover, we further assessed the pathogenicity of four recurrent variants ((DYSF, c.4076T > C), (GMPPB, c.458C > T), (SGCA, c.739G > A) (TTN, c.7331G > A), designated their neurological impact and added new phenotypes in patients with these variants. To our knowledge, this is the first study applying an ES-based comprehensive molecular diagnosis to Jordanian cohort with MDs. Our findings confirmed that ES is a powerful approach for the diagnosis of MD patients. This efficient method of molecular diagnosis is crucial for guiding patient clinical care, genetic counseling, and most importantly, paving the way for gene therapy which is currently in clinical trials.