Choline acetyltransferase mutations cause myasthenic syndrome associated with episodic apnea in humans

Choline acetyltransferase (ChAT; EC 2.3.1.6) catalyzes the reversible synth esis of acetylcholine (ACh) from acetyl CoA and choline at cholinergic syna pses. Mutations in genes encoding ChAT affecting motility exist in Caenorha bditis elegans and Drosophila, but no CHAT mutations have been observed in humans to date. Here we report that mutations in CHAT cause a congenital my asthenic syndrome associated with frequently fatal episodes of apnea (CMS-E A), Studies of the neuromuscular junction in this disease show a stimulatio n-dependent decrease of the amplitude of the miniature endplate potential a nd no deficiency of the ACh receptor. These findings point to a defect in A Ch resynthesis or vesicular filling and to CHAT as one of the candidate gen es. Direct sequencing of CHAT reveals 10 recessive mutations in five patien ts with CMS-EA, One mutation (523insCC) is a frameshifting null mutation. T hree mutations (1305T, R420C, and E441K) markedly reduce ChAT expression in COS cells. Kinetic studies of nine bacterially expressed ChAT mutants demo nstrate that one mutant (E441K) lacks catalytic activity, and eight mutants (L21OP, P211A, 1305T, R420C, R482G, S498L V506L and R560H) have significan tly impaired catalytic efficiencies.