Linkage studies in a kindred from Oklahoma, with familial benign (hypocalciuric) hypercalcaemia (FBH) and developmental elevations in serum parathyroid hormone levels, indicate a third locus for FBH.

A five-generation kindred (19 affected, two obligate carriers and 20 unaffected) from Oklahoma USA, in which familial benign (hypocalciuric) hypercalcaemia (FBH) was associated with a developmental elevation in serum parathyroid hormone (PTH) levels, has been investigated for linkage to the candidate chromosomal regions 3q21-q24 and 19p13.3, 11q13, and 11p15, to which the genes for FBH, multiple endocrine neoplasia type 1 (MEN1) and PTH have been mapped respectively. By means of 17 polymorphic markers from these regions, linkage was excluded [LOD scores < -2.00 at (theta) = 0.05-0.25]. In addition, an analysis of multipoint crossovers and use of the LINKMAP program confirmed the exclusion from these regions. Thus, this form of FBH, designated the Oklahoma variant FBH(Ok), is not linked to markers that segregate with FBH, MEN1 and PTH; our results indicate further genetic heterogeneity and the presence of a third locus for FBH.