Congenital myasthenic syndrome with episodic apnea in patients homozygous for a CHAT missense mutation.

BACKGROUND The syndrome of congenital myasthenia with episodic apnea (CMS-EA) was previously found to be due to mutations in the choline acetyltransferase gene (CHAT). OBJECTIVE To identify the mutations underlying CMS-EA in a Turkish multiplex family. DESIGN Direct sequencing of the CHAT gene. PATIENTS A consanguineous Turkish family with 2 siblings affected by muscular weakness and episodic respiratory distress. RESULTS The sequencing of CHAT coding exons identified a previously unknown missense mutation that affected a highly conserved amino acid residue (I336T). The mutation was absent in 164 control chromosomes. CONCLUSIONS The high degree of conservation in different species strongly suggests that I336T is a functionally important amino acid residue. The absence of I336T from a large control sample further supports the pathogenic role of I336T in CMS-EA. This is the second report of CHAT mutations causing presynaptic CMS.