Andersen-Tawil syndrome associated with a subclinical maternal carrier of a KCNJ2 mutation

A man in his mid-20s presented with recurrent episodes of muscle weakness and periodic paralysis suggesting a possible channelopathy. Neurological assessment during symptomatic episodes confirmed muscle weakness while biochemical testing confirmed hypokalaemia. Genetic analysis through whole-exome sequencing identified a heterozygous pathogenic KCNJ2 variant (c.245G>A; p.Arg82Gln), which was confirmed by Sanger sequencing and found to be maternally inherited. The mother was asymptomatic, consistent with a subclinical carrier state. In silico analysis provided supportive computational evidence for the pathogenic classification of the variant. This case highlights the variable expressivity of Andersen-Tawil syndrome and the diagnostic difficulty when the classical triad is incomplete. It emphasises the importance of considering genetic testing in patients with unexplained periodic paralysis and the value of family studies for accurate diagnosis, counselling and management in autosomal dominant channelopathies.