Magnesium excretion in idiopathic hypercalciuria

Magnesium status in idiopathic calcium urolithiasis--an orientational study in younger males

With the aim of revealing a possible magnesium (Mg) deficiency in the aetiology of idiopathic recurrent calcium urolithiasis we studied the Mg content of red blood cells, serum total, protein-bound, ionised and complexed fractions of Mg, and urinary Mg after an overnight fast. The two study groups comprised 12 male recurrent calcium urolithiasis patients and 12 healthy male controls (mean age 31 and 29 years, respectively). In recurrent calcium urolithiasis, serum albumin and Mg of erythrocytes were significantly decreased, as was serum total and protein-bound Mg, whereas serum ultrafiltrable, ionised and complexed Mg were statistically indistinguishable from values in controls. Urinary Mg (per unit creatinine) in recurrent calcium urolithiasis (mean 0.188 vs 0.209 in controls; p = 0.386) was not statistically different, whereas urinary total protein, glucose, and pH were significantly increased. The renal clearances of Mg and glucose were positively correlated (r = 0.56; p < 0.01), with a steeper slope in recurrent calcium urolithiasis than controls. Further fractionation of serum and urinary Mg into ions and complexes in recurrent calcium urolithiasis subjects with identical creatinine clearance revealed no statistical difference between 1) Mg ions and complexes filtered by renal glomeruli; 2) Mg ions and complexes excreted in urine; 3) fractional Mg excretion. Median urine supersaturation with respect to calcium oxalate was insignificantly lower (1.5 vs 2.2), with respect to hydroxyapatite insignificantly higher (3.3 vs 1.8), than in controls. It is concluded that relatively young recurrent calcium urolithiasis patients exhibit a deficiency of Mg in erythrocytes and serum total Mg, but no alteration of renal Mg handling. Thus, in recurrent calcium urolithiasis, a role of Mg deficiency in urine as a factor initiating stone formation may be ruled out, whereas a possible link between cellular Mg deficiency and the impairment of renal tubular functions involved in reabsorption of glucose and proteins, and in urine acidification, deserves further studies.

Hypomagnesaemia of hereditary renal origin

Cases of hypomagnesaemia of hereditary renal origin represent at least three different congenital disorders of tubular reabsorption of magnesium (Mg). Isolated familial hypomagnesaemia has been reported in a heterogeneous group of patients and an autosomal dominant pattern of inheritance has often been found to be present. Familial hypokalaemia-hypomagnesaemia, inherited as an autosomal recessive trait, has been reported in 17 patients and we now describe 3 additional cases. Hypomagnesaemia is accompanied by hypokalaemia, metabolic alkalosis, hypocalciuria and moderate sodium chloride wasting. Titration of renal Mg reabsorption indicates the presence of a low threshold but a normal Tm. The inherited defect is probably situated at the level of the distal convoluted tubule and mimics the therapeutic effect of thiazides. This condition is frequently confused with Bartter's syndrome. Familial hypomagnesaemia-hypercalciuria, also inherited as an autosomal recessive trait, has been reported in at least 15 patients and we now add 3 new cases. Hypomagnesaemia is always accompanied by hypercalciuria and nephrocalcinosis. Ocular abnormalities such as myopia and horizontal nystagmus are often present. Hypermagnesiuria is of a greater degree than that observed in the previous entity and reflects a low Tm of Mg reabsorption. The defect must be situated at the level of the ascending limb of the loop of Henle and affects the transport of both calcium and Mg but not of sodium and chloride. This condition has not been clearly separated from hereditary distal renal tubular acidosis in the literature.