REDUCED NA-ATPASE ACTIVITY IN PATIENTS WITH PSEUDOHYPOALDOSTERONISM(,K+)

Pseudohypoaldosteronism is a hereditary salt-wasting syndrome usually seen in infancy with weight loss, dehydration, and failure to thrive. The patho-physiologic origin of pseudohypoaldosteronism is unknown. Th e defect could be related to the unresponsiveness of target organs to mineralocorticoids resulting in hyponatremia, hyperkalemia, and marked ly elevated plasma aldosterone and renin levels. Red blood cell Na+,K-ATP-ase activity was measured in a pair of twins with pseudohypoaldos teronism, in an unrelated child with hypoaldosteronism, and in an age- matched group of 50 healthy infants and young children. The enzyme was assayed by a method that couples ATP hydrolysis with NADH oxidation. Plasma renin and aldosterone levels were measured by RIA. Red blood ce ll Na+,K+-ATPase activity in the twins with pseudohypoaldosteronism wa s very low at the time of diagnosis (3 wk). In both twins a time-relat ed gradual increase in enzyme activity was observed during the Ist mo of life, reaching control values between 6 and 8 mo of age. This incre ase was associated with both a reduction in salt requirement and clini cal improvement. Plasma renin activity and aldosterone levels were ver y high at the time of diagnosis. Plasma renin activity reverted gradua lly to normal values, whereas aldosterone levels remained high through out the follow-up period. The child with hypoaldosteronism had normal Na+,K+-ATPase activity at diagnosis and during follow-up.