SCN4A and paramyotonia congenita of Von Eulenburg: Gain of Function (GoF) of Nav1.4 (i.e., an overactive channel) is now known to cause a spectrum of three clinically delineated dominantly-inherited neuromuscular disorders with overlapping clinical symptoms: sodium channel myotonia (SCM), paramyotonia congenita (PMC) and primary periodic paralyses (PP) (Cannon, 2018).