45. Incomplete renal tubular acidosis with hypercalcinria in siblings

Abstract

Two female siblings were first seen at the age of 7 and 9 years with a recent history of pyclonephritis. On admission, polyuria, hypercalciuria (up to 10 mg/kg 24 hr), and advanced nephrocalcinosis were noticed. Growth was normal. Rental function studies revealed leukocyturia, protenuria, moderately decreased glomerular filtratin rate, impaired concentrating capacity, an acidification defect (minimal urinary pH 5.4 days after 150 mEq/m2/24 hr of NH4Cl), a normal HCO3 threshold, and a low citrate excretion. Under basal conditions, acidosis was never observed. Potassium metabolism and amino acid excretion were normal. Radiological examination showed slight osteoporosis. In a kidney biopsy patchy interstitial fibrosis and glomerular sclerosis were reported. Increased calcium absorption by the gut was excluded by following the calciuria during prolonged starvation and the activity of Ca17 (200 nCi p. os) in the whole body and in the stools. Phospate reabsorption in the kidney rose as in normal subjects after a Ca infusion. but insufficientyly after administration of parathyroid hormone. Treatment with a diet low in Ca resulted in a fall of the Ca excretion with a negative Ca balance. By a salt restricted diet, given over 6 months, the balance increased considerably and the calciuria became normal. Hydrochlorothiazide provoked hypocalcemic tetany. The father of the siblings is a past stone former, has a high Ca excretion, but can acidity his urine normally. It is believed that these girls present an incomplete familial form of (distal) tubular acidosis distinct from other types of tubular acidosis and form idiopathic hypercalciuria.