PRELIMINARY LOCALIZATION OF A GENE FOR AUTOSOMAL-DOMINANT HYPOPARATHYROIDISM TO CHROMOSOME 3Q13

A large family in which hypoparathyroidism was observed to segregate a s an autosomal dominant trait in three generations was identified. Mut ation in the PTH gene was excluded by linkage and single-stranded conf ormational analysis. The hypocalcemic phenotype in this family was map ped by linkage analysis using short, tandem-repeat polymorphisms to th e region of chromosome 3q13. A maximum led score of 2.71 at Theta = 0. 0 was observed with marker D3S1303. Positive lod scores were observed at Theta = 0.0 with markers flanking D3S1303. Multipoint linkage analy sis gave a lod score of 2.71 for the region flanking D3S1303. Simulati on using the computer program SLINK showed that a led score of 2.71 at Theta = 0.0 was the maximum lod score possible given the pedigree str ucture. The simulation also showed that given the structure of the ped igree the probability of observing a lod score of 2.71 at Theta = 0.0 by chance was 1 in 1000. The data presented above provide important pr eliminary evidence supporting linkage to chromosome 3q13. This region contains a Ca2+-sensing receptor gene that is proposed as a key signal transduction element for changes in extracellular Ca2+ concentrations in mechanisms of regulation of PTH secretion from parathyroid cells. The mutation in this family may activate the Ca2+-sensing receptor sup pressing PTH secretion and lowering the ''set point'' for serum calciu m levels.