SCN4A and congenital myasthenic syndrome: These more severe cases comprise patients with mutations in genes that are components of the nonselective sodium leak channel complex (NALCN channelosome) and—depending on the inheritance pattern—either present with muscular hypertonia and distal contractures (Karakaya et al. 2016) or hypotonia, psychomotor retardation, and dysmorphic features (Bramswig et al. 2018), as well as patients with mutations in the sodium voltage-gated channel α subunit 4 gene (SCN4A), which may present with congenital myopathy or as congenital myasthenic syndrome (Sloth et al. 2018; Elia et al. 2019).