Recessive congenital myasthenic syndrome caused by a homozygous mutation in SYT2 altering a highly conserved C-terminal amino acid sequence.

Defects in the gene encoding synaptotagmin 2 (SYT2) have been linked to a presynaptic congenital myasthenic syndrome (CMS) and motor neuropathies. However, to date only dominant forms of the disease have been described. We report here a consanguineous patient with a severe recessive form of presynaptic CMS and denervation atrophy caused by the homozygous mutation c.1191delG, p.Arg397Serfs*37 in SYT2. The affected 2-year-old girl had profound weakness and areflexia with moderate bulbar deficit. Repetitive nerve stimulation revealed an extreme reduction of compound muscle action potential amplitudes at rest, with a striking facilitation followed by a progressive decline at fast stimulation rates. These findings were reminiscent, but not identical to those seen in the Lambert-Eaton myasthenic syndrome. 3,4 diaminopyridine and pyridostigmine were effective to ameliorate muscle fatigue, but albuterol was ineffective. Modeling of the mutation using the rat Syt1 C2B x-ray structure revealed that Arg397Serfs*37 disrupts a highly conserved amino acid sequence at the bottom face of the C2B domain not directly involved in calcium binding, but crucial for synaptotagmin-SNARE interaction and exocytosis. Thus, this report describes a recessive form of synaptotagmin 2-CMS and highlights the importance of the synaptotagmin C-terminal on synaptic vesicle fusion and exocytosis. © 2020 Wiley Periodicals, Inc.

Citation

Ricardo A Maselli, Hélio van der Linden, Michael Ferns. Recessive congenital myasthenic syndrome caused by a homozygous mutation in SYT2 altering a highly conserved C-terminal amino acid sequence. American journal of medical genetics. Part A. 2020 Jul;182(7):1744-1749

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PMID: 32250532

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