SCN4A and congenital myasthenic syndrome: The first published report (p.S246L/p.V1442E) was notable for pronounced CMAP decrement during repetitive nerve stimulation (at 2 Hz after a 10 Hz load and at all frequencies of 10 Hz or higher).5 For the 2 subsequent single-case reports of SCN4A-associated congenital myasthenic syndrome (CMS), one had increased jitter7 (as observed for patient F1 III-3 herein) but neither had a CMAP decrement with repetitive stimulation.