Three novel activating mutations in the calcium-sensing receptor responsible for autosomal dominant hypocalcemia

We report three novel activating mutations in the calcium-sensing receptor (CASR) that are responsible for autosomal dominant hypocalcemia (ADH) in th ree unrelated families. Each mutation involves a missense substitution resu lting in a nonconservative amino acid alteration, P221L, E228Q, and Q245R. These mutations were observed in affected family members, but not in unaffe cted family members or in unrelated control samples. All three mutations ar e clustered in the extracellular domain of the CASE in a region dominated b y negatively charged amino acids. Each mutant and wild-type receptor was ex pressed in Cos-l cells. A luciferase reporter gene assay was utilized to de tect the level of receptor activity by utilizing a protein kinase C-activat ed promoter to drive the production of luciferin, the reporter gene product . All three mutant receptors exhibited an increased sensitivity to calcium at all concentrations tested when compared to the wild-type receptor, suppo rting the hypothesis that these are activating mutations and are responsibl e for the ADH phenotype in these families. The data presented in this study suggest the importance of this highly negatively charged region of the ext racellular domain in normal CASE function, (C) 2000 Academic Press.