Synaptotagmin 2 Mutations Cause an Autosomal-Dominant Form of Lambert-Eaton Myasthenic Syndrome and Nonprogressive Motor Neuropathy

Herrmann DN, Horvath R, Sowden JE, Gonzales M, Sanchez-Mejias A, Guan Z, Whittaker RG, Almodovar JL, Lane M, Bansagi B, Pyle A, Boczonadi V, Lochmüller H, Griffin H, Chinnery PF, Lloyd TE, Littleton JT, Zuchner S


The American Journal of Human Genetics 95, 332–339, September 2014
DOI: 10.1016/j.ajhg.2014.08.007

Abstract

Synaptotagmin 2 is a synaptic vesicle protein that functions as a calcium sensor for neurotransmission but has not been previously associated with human disease. Via whole-exome sequencing, we identified heterozygous missense mutations in the C2B calcium-binding domain of the gene encoding Synaptotagmin 2 in two multigenerational families presenting with peripheral motor neuron syndromes. An essential calcium-binding aspartate residue, Asp307Ala, was disrupted by a c.920A>C change in one family that presented with an autosomal-dominant presynaptic neuromuscular junction disorder resembling Lambert-Eaton myasthenic syndrome. A c.923C>T variant affecting an adjacent residue (p.Pro308Leu) produced a presynaptic neuromuscular junction defect and a dominant hereditary motor neuropathy in a second family. Characterization of the mutation homologous to the human c.920A>C variant in Drosophila Synaptotagmin revealed a dominant disruption of synaptic vesicle exocytosis using this transgenic model. These findings indicate that Synaptotagmin 2 regulates neurotransmitter release at human peripheral motor nerve terminals. In addition, mutations in the Synaptotagmin 2 C2B domain represent an important cause of presynaptic congenital myasthenic syndromes and link them with hereditary motor axonopathies.

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