Mineralocorticoid unresponsiveness with severe neonatal hyponatremia and hyperkalemia.

An infant with severe neonatal hyponatremia and hyperkalemia is described. Although marked elevations of urinary 17-hydroxycorticosteroids suggested an 18-dehydrogenase aldosterone biosynthetic defect, the infant proved to have mineralocorticoid unresponsiveness, or pseudohypoaldosteronism. Dietary sodium supplementation and ion exchange resin administration resulted in normalization of serum electrolytes and urinary 17-hydroxycorticosteroids. ACTH infusion produced natriuresis, suggesting the need for additional sodium supplementation during the stress of illness, with a resultant increase in ACTH secretion. Determinations of the relative amounts of urinary 18-hydroxy and aldosterone metabolites appear necessary for early definitive diagnosis of the disorder.