Exome sequencing and microarray identified a novel large exonic deletion in gene in an ultra-rare case with recessive CMS type 7.

Congenital myasthenic syndromes (CMSs) are a diverse group of diseases that have an underlying defect in transmission of signals from nerve cells to muscles that lead to muscular weakness. A 13-year-old male child born of consanguineous parents with profound motor developmental delay and normal cognition was referred to us. The younger male sibling aged 9 months was similarly affected. Electromyography (EMG) and nerve conduction studies revealed CMS. Clinical exome sequencing revealed a novel large deletion including the exons 2 to 9 of gene which confirmed the diagnosis of presynaptic CMS type 7 in the siblings. The deletion was confirmed on a chromosomal exon microarray. The parents were confirmed carriers of the same mutation and were normal on clinical and EMG studies. This is the second case of CMS type 7 described with a large deletion of gene, a first case with gene mutation from India and overall 10th recessive case in the world.