title: Choline Acetyltransferase Mutations Causing Congenital Myasthenic Syndrome: Molecular Findings and Genotype-Phenotype Correlations.
abstract: Choline acetyltransferase catalyzes the synthesis of acetylcholine at cholinergic nerves. Mutations in human CHAT cause a congenital myasthenic syndrome due to impaired synthesis of ACh; this severe variant of the disease is frequently associated with unexpected episodes of potentially fatal apnea. The severity of this condition varies remarkably, and the molecular factors determining this variability are poorly understood. Furthermore, genotype-phenotype correlations have been difficult to establish in patients with biallelic mutations. We analyzed the protein expression of phosphorylated ChAT of seven CHAT mutations, p.Val136Met, p.Arg207His, p.Arg186Trp, p.Val194Leu, p.Pro211Ala, p.Arg566Cys, and p.Ser694Cys, in HEK-293 cells to phosphorylated ChAT, determined their enzyme kinetics and thermal stability, and examined their structural changes. Three mutations, p.Arg207His, p.Arg186Trp, and p.Arg566Cys, are novel, and p.Val136Met and p.Arg207His are homozygous in three families and associated with severe disease. The characterization of mutants showed a decrease in the overall catalytic efficiency of ChAT; in particular, those located near the active-site tunnel produced the most seriously disruptive phenotypic effects. On the other hand, p.Val136Met, which is located far from both active and substrate-binding sites, produced the most drastic reduction of ChAT expression. Overall, CHAT mutations producing low enzyme expression and severe kinetic effects are associated with the most severe phenotypes.
authors.affiliation: Department of Neurology, University of California Davis, Davis, California.
authors.forename: Juan
authors.initials: J
authors.lastname: Arredondo
authors.affiliation: Department of Neurology, University of California Davis, Davis, California.
authors.forename: Marian
authors.initials: M
authors.lastname: Lara
authors.affiliation: Departments of Neurology and Pediatrics, University of Washington, and Seattle Children's Hospital, Seattle, Washington.
authors.forename: Sídney M
authors.initials: SM
authors.lastname: Gospe
authors.affiliation: Department of Neurology, Instituto de Investigaciones Médicas A Lanari-UBA, Buenos Aires, Argentina.
authors.forename: Claudio G
authors.initials: CG
authors.lastname: Mazia
authors.affiliation: Servicio de Neurología Pediátrica, Hospital Italiano, Buenos Aires, Argentina.
authors.forename: Maria
authors.initials: M
authors.lastname: Vaccarezza
authors.affiliation: Sector Enfermedades Neuromusculares Hospital de Niños "Ricardo Gutiérrez", Buenos Aires, Argentina.
authors.forename: Marcela
authors.initials: M
authors.lastname: Garcia-Erro
authors.affiliation: Department of Neurology, University of California Davis, Davis, California.
authors.forename: Constance M
authors.initials: CM
authors.lastname: Bowe
authors.affiliation: Department of Neurology, University of California Davis, Davis, California.
authors.forename: Celia H
authors.initials: CH
authors.lastname: Chang
authors.affiliation: Division of Neurology, University of British Columbia, Vancouver, Canada.
authors.forename: Michelle M
authors.initials: MM
authors.lastname: Mezei
authors.affiliation: Department of Neurology, University of California Davis, Davis, California.
authors.forename: Ricardo A
authors.initials: RA
authors.lastname: Maselli
mesh_terms: D000293:Adolescent; D000483:Alleles; D019943:Amino Acid Substitution; D001665:Binding Sites; D020134:Catalytic Domain; D002675:Child, Preschool; D002795:Choline O-Acetyltransferase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004252:DNA Mutational Analysis; D004789:Enzyme Activation; D005260:Female; D015870:Gene Expression; D056726:Genetic Association Studies; D005838:Genotype; D057809:HEK293 Cells; D006801:Humans; D006860:Hydrogen Bonding; D008297:Male; D008958:Models, Molecular; D009154:Mutation; D020294:Myasthenic Syndromes, Congenital / Q000175:diagnosis / Q000235:genetics*; D010766:Phosphorylation; D011487:Protein Conformation; D013379:Substrate Specificity
chemical_list: D002795:Choline O-Acetyltransferase
keywords: ChAT; enzyme kinetics; genotype-phenotype correlations; phosphorylation