Case Report of Andersen-Tawil Syndrome: Rare Presentation of a Rare Disease.

Andersen-Tawil syndrome (ATS) is a rare genetic disorder characterized by a triad of periodic paralysis, cardiac arrhythmias, and dysmorphic features, typically presenting in the first two decades of life. A 45-year-old man presented with acute lower motor neuron-type quadriparesis. He reported similar self-resolving episodes over the past 2 years, triggered by rest after exercise. There were no cardiac symptoms, dysmorphic features, or relevant family history. Biochemical evaluation revealed hypokalemia. Genetic testing confirmed a heterozygous nonsense mutation in the KCNJ2 gene (c.13C>T, p.Arg5Ter). Cardiac and dental evaluations were normal. He was treated with potassium supplementation and later acetazolamide, with no recurrence over 2 years. This case highlights a rare adult-onset presentation of ATS without cardiac or dysmorphic features and a negative family history, contributing to the limited adult ATS literature.