• Objective.
—To describe defective aldosterone biosynthesis (corticosterone methyl oxidase type II [CMO-II] deficiency) in a kindred with hyperkalemic periodic paralysis.
Setting.
—Tertiary care hospital in Madison, Wis.
Patients.
—Individuals studied included a female infant with failure to thrive, hyponatremia, and hyperkalemia; the infant's asymptomatic mother and father; and a maternal aunt and grandmother with hyperkalemic periodic paralysis.
Interventions.
—Mineralocorticoid synthetic pathways were analyzed with synthetic adrenocorticotropin stimulation. In one patient with hyperkalemic periodic paralysis, acetazolamide sodium therapy was discontinued and replaced with fludrocortisone acetate therapy.
Measurements/Main Results.
—Impaired aldosterone synthesis with marked accumulation of mineralocorticoid precursors 18-hydroxycorticosterone and corticosterone indicated severe CMO-II deficiency in the infant. In her relatives and parents, baseline aldosterone levels (74 to 111 pmol/L) were low (reference range, 194 to 830 pmol/L, a nonstricted sodium diet). Serum 18-hydroxycorticosterone levels (442 to 1021 pmol/L) were normal (reference range, 138 to 1270 pmol/L), but ratios of 18-hydroxycorticosterone to aldosterone were abnormally elevated (4.5 to 13.7; reference range, 2.65±1.86), indicating deficient CMO-II enzyme activity. Acetazolamide therapy was substituted with fludrocortisone therapy in the maternal aunt without return of paralytic symptoms.
Conclusion.
—This association of hyperkalemic periodic paralysis with CMO-II deficiency and resolution of paralytic episodes with fludrocortisone therapy suggests a contribution of defective mineralocorticoid-mediated potassium homeostasis to the pathogenesis of hyperkalemic periodic paralysis.
