FAMILIAL HYPOMAGNESEMIA WITH HYPERCALCIURIA AND NEPHROCALCINOSIS

Very few patients with familial hypomagnesemia, hypercalciuria and nep hrocalcinosis have been described. Information about clinical course, familial studies or evolution after renal transplantation is very scan t. We have studied eight patients with this syndrome who belong to fiv e different families. The mean age at diagnosis was 15 +/- 7 years (5 to 25 years). The primary clinical data were polyuria-polydipsia (8 ca ses), ocular abnormalities (5), recurrent urinary tract infections (5) and recurrent renal colics with stone passage (2). Bilateral nephroca lcinosis was observed in all cases. Every patient showed hypomagnesemi a (1.1 +/- 0.2 mg/dl) with inappropriately high urinary magnesium (Mg) excretions (70 +/- 17 mg day), Mg clearances (4.4 +/- 1.2 ml/m) and M g fractional excretions (16.2 +/- 7.1%). Hypercalciuria was present in every case except in those with advanced renal insufficiency. Serum p arathormone levels were abnormally high. Serum calcium (Ca), phosphoru s and potassium, and urinary excretions of uric acid and oxalate were normal. Neither chronic oral Mg administration nor thiazide diuretics normalized serum Mg levels or urinary Ca excretions, respectively. Fol low-up was 6 +/- 4.5 years. Renal function worsened in every case with six patients starting on chronic dialysis after 4.3 +/- 3.8 years. Th e progression rate of renal insufficiency correlated with the severity of nephrocalcinosis. Five patients have received a kidney graft, and their serum Mg and urinary Ca have always been within normal values af ter transplantation. Twenty-six members; of four of the affected famil ies were studied: none of them showed hypomagnesemia, renal insufficie ncy or nephrocalcinosis. However, eleven cases (42%) had hypercalciuri a and four of them presented with recurrent renal stones. Two family m embers had medullary sponge kidneys. In conclusion, progression to ren al insufficiency is common in this syndrome; oral Mg and thiazide diur etics are ineffective to correct abnormalities. After kidney graft, tu bular handling of Mg and Ca was normal. A striking incidence (42%) of hypercalciuria was found in the familial study.