In this study, 37 first-degree relatives of 13 children with idiopathic hypercalciuria (IH) from 12 families are presented. We demonstrated that IH may occur in two patterns of inheritance: familial or non-familial. Since all of the 18 first-degree relatives of six patients with IH were normocalciuric, it was suggested that these patients had the non-familial form of IH. There was no history of urolithiasis in the relatives of these six patients. Of 26 members from the remaining six families, 13 including seven children with IH and six of their first-degree relatives had hypercalciuria. This data indicates that IH occurred in a familial form in this group. The occurrence of the familial form of IH among our 13 patients with IH was 53.8 percent and the frequency of hypercalciuria in the first-degree relatives of these patients with familial IH was 50 percent. Eight members including two children with IH and six first-degree and more distant relatives from the six families of seven patients with familial IH had urolithiasis. Our findings support the idea that the familial form of IH is transmitted as an autosomal dominant trait and urinary tract stones may be formed in relatives of patients with familial IH. It should be emphasized that the families of people with IH and/or urolithiasis be followed-up closely to prevent the occurrence of calcium stones since IH is known as an important cause of calcium stone formation and 80-90 percent of patients with IH are asymptomatic.

Keywords: familial hypercalciuria, idiopathic hypercalciuria, urolithiasis (urinary tract stone disease), calcium stone, autosomal dominant inheritance