Bumetanide in Hypokalaemic Periodic Paralysis

Inclusion Criteria: * At least 18 years of age; * Diagnosis of genetically confirmed HypoPP; * Clinical symptoms or signs of active symptomatic disease (at least 1 attack in last 12 months); * Practising an acceptable method of birth control for the duration of the trial. This will be addressed on Patient Information Sheet for men and women (section 11.4.5); Exclusion Criteria: * Inability or unwillingness to provide informed consent; * People older than 64 years old; * Other conditions causing hand weakness which could interfere with study measurements (e.g. due to a stroke, trauma or arthritis) * Patients with a history of cardiac disease, renal failure or moderate to severe hepatic disease. Note: abnormalities in serum transaminases are common in people with HypoPP as they arise from skeletal muscle rather than any specific liver abnormality. Consequently, raised serum bilirubin \>20% above the baseline value will be used to identify abnormal liver function; * Women who are pregnant or breast-feeding; * Patients with a current or previous history of diabetes, porphyria, symptomatic hypotension, prostatic hypertrophy or difficulty with micturition, allergy to sulfonamides or thiazides; * Patients on lithium, digoxin, nephro- or ototoxic drugs; * Patients known to be allergic bumetanide or its excipients; * Patients with a history of inadequately treated Addison's disease; * Patients participating in another interventional trial in the previous 1 month.