Mapping a gene defect in absorptive hypercalciuria to chromosome 1q23.3-q24

Absorptive hypercalciuria (AH), a common cause of kidney stones, is due to intestinal hyperabsorption of calcium. The presence of a family history of nephrolithiasis, in about half of the affected individuals studied indicates that an inherited genetic defect is one likely cause of AH. Although it is known that intestinal calcium absorption is regulated by a number of factors, the molecular biological basis for the increased calcium absorption in AH is unknown. This study was designed to determine the chromosomal locus of the gene defect linked to the AH phenotype in three families with a severe form of AH. Three kindreds were evaluated in a systematic autosomal genomewide linkage analysis study. The AH phenotype, characterized by hyperabsorption of calcium and hypercalciuria, was linked to only one chromosomal locus, 1q23.3-q24. A 2-point logarithm of odds score of 3.3 was obtained with markers D1S318 and D1S196 at a recombination frequency of θ = 0. Nonparametric multipoint linkage analysis yielded a peak nonparametric linkage Z(aII)-score of 12.7, P = 6 x 10^-6. Analysis of key recombinants within the families studied localized the gene to a 4.3-megabase region between markers D1S2681 (centromere) and D1S2815. A trait associated with intestinal hyperabsorption of calcium in a severe form of absorptive hypercalciuria has been mapped to chromosome 1q23.3-q24.