Compound heterozygous CHAT gene mutations, a missense and a splice site variant, in two siblings with congenital myasthenic syndrome

Mutations in the choline acetyltransferase (CHAT) gene cause congenital myasthenic syndrome (CMS). Episodic apnea is frequently observed in patients with CMS due to CHAT mutations (CMS-CHAT), and muscle hypotonia at birth or in early infancy is also common. We report two siblings with compound heterozygous mutations in the CHAT gene: c.1231G > A (missense) and c.752 + 2 T > C (splice site). To confirm the splice site mutation induces a splicing variant, we performed a minigene assay and demonstrated that the splice site mutation, c.752 + 2 T > C, results in complete exon skipping. AlphaFold2 analysis predicted that the skipped exon constitutes an α helix, a highly conserved core structural element of ChAT. These structural alterations in ChAT may underlie the clinical phenotype associated with these mutations.