To better clarify the genetic inheritance of primary tubular hypomagnesemia-hypokalemia with hypocalciuria, or Gitelman's syndrome (GS), we studied eight families (10 patients aged 11 to 22 years; 16 parents; 9 siblings) in which at least one offspring had GS (plasma magnesium < 0.65 mmol/liter; plasma potassium < 3.6 mmol/liter; high magnesium and potassium fractional excretions; molar urinary calcium/creatinine < 0.10). Two families each had two offspring of different sex with GS, who all had tetanic episodes and/or marked weakness during childhood or adolescence, whereas in three other families two mothers and three offspring presented GS and one father and two other offspring had hypomagnesemia and hypocalciuria but normal plasma potassium. The mean plasma magnesium and potassium levels of the patients of the first two families were significantly lower (P < 0.05) than those of the other three families. Intralymphocytic but not intraerythrocytic magnesium and potassium were significantly lower (P < 0.05) in patients compared to controls. We hypothesize that there are two different types of genetic transmission of GS, one autosomal recessive and one autosomal dominant with high phenotype variability. It seems that this genetic heterogeneity is associated with a different clinical expression with frequent tetanic episodes and lower plasma potassium and magnesium levels in the autosomal recessive form.

The volume/pressure (V/P) curve of the total respiratory system in paralysed patients is drawn assuming that volume changes of the respiratory system (delta V resp) equals volume displacement of the measuring apparatus (delta V syr), usually a supersyringe. However, in 93 VP curves we found that O2 removed from the lung-syringe system during the procedure (proportional to the time) largely exceeds the CO2 added to the lung-syringe system (delta V gas). This results in a net loss of volume from the system (delta V resp less than delta V-syr). Deflation compliance, hysteresis area and ratio are significantly affected by this phenomenon. Inflation compliance is less influenced by delta V gas, partially compensated by the intrapulmonary gas expansion due to the temperature changes. We conclude that the parameters computed on the deflation limb of V/P curve are misleading if proper correction of the volume scale is not introduced.

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The metabolism of potassium and magnesium are closely linked (in situations where potassium and magnesium depletion coexist, magnesium restoration alone is sufficient to correct hypokalemia). Moreover, magnesium deficiency blunts the interplay between circulating calcium and the calciotropic hormones. Renal magnesium wasting, hypokalemia, alkalosis, hypocalciuria, and a tendency towards hypocalcemia characterize Gitelman syndrome. Plasma or intracellular potassium, circulating calcium, and calciotropic hormones were therefore investigated in eight patients (4 females, 4 males, aged 9-20 years) with Gitelman syndrome before and during oral supplementation with magnesium pyrrolidone carboxylate 30 mmol daily for 4 weeks. Magnesium supplementation significantly increased plasma and intracellular magnesium and plasma calcium, but failed to completely restore magnesium deficiency. In contrast, blood levels of parathyroid hormone and calcitriol and plasma and intracellular potassium were not modified following magnesium administration.

The long-term follow-up (from age 6 to 20 years) of a girl with Gitelman's syndrome, who had four hypomagnesaemic-tetanic episodes associated with normal plasma calcium, hypokalemia and hypocalciuria, is presented. During and after puberty, hypomagnesaemia was of the order of 0.41-0.49 mmol/l and plasma potassium was at the lower reference limit. The long-term clinical course and growth of this patient appeared good, but, magnesium supplementation reduces the risk of tetanic crises.