Copy number analysis reveals a novel multiexon deletion of the gene in congenital myasthenia.

Congenital myasthenic syndrome (CMS) is genetically and clinically heterogeneous. Despite a considerable number of causal genes discovered, many patients are left without a specific diagnosis after genetic testing. The presumption is that novel genes yet to be discovered will account for the majority of such patients. However, it is also possible that we are neglecting a type of genetic variation: copy number changes (>50 bp) as causal for some of these patients. Next-generation sequencing (NGS) can simultaneously screen all known causal genes and is increasingly being validated to have a potential to identify copy number changes. We present a CMS case who did not receive a genetic diagnosis from previous Sanger sequencing, but through a novel copy number analysis algorithm integrated into our targeted NGS panel, we discovered a novel copy number mutation in the gene and made a genetic diagnosis. This discovery expands the genotype-phenotype correlation of CMS, leads to improved genetic counsel, and allows for specific pharmacologic treatment..