CACNA1S and Hypokalemia: Hypokalaemic periodic paralysis (HOKPP), including HOKPP1 (OMIM #170400) and HOKPP2 (OMIM #613345), is a rare autosomal dominant inherited disease characterised by episodic muscle weakness with significant hypokalaemia (< 0.9 to 3.0 mmol/L) during attacks [5, 6].