A proposed mutation, Val781Ile, associated with hyperkalemic periodic paralysis and cardiac dysrhythmia is a benign polymorphism

Twenty different point mutations have been identified in the gene coding for the α subunit of the adult skeletal muscle sodium channel in families with hyperkalemic periodic paralysis, paramyotonia congenita, and the potassium-aggravated myotonias. One novel mutation (Va1781Ile) was reported in an adopted boy with potassium-sensitive weakness and cardiac dysrhythmia. The confidence in establishing this rare amino acid substitution as a causative mutation was limited by the absence of family members for segregation analysis. Functional expression studies herein show that Va1781Ile is most likely a benign polymorphism and not a disease-associated mutation.