PSEUDOHYPOPARATHYROIDISM TYPE IB IS NOT CAUSED BY MUTATIONS IN THE CODING EXONS OF THE HUMAN PARATHYROID-HORMONE (PTH) PTH-RELATED PEPTIDE RECEPTOR GENE/

Pseudohypoparathyroidism type Ib (PHP-Ib) is thought to be caused by a PTH/PTH-related peptide (PTHrP) receptor defect. To search for recept or mutations in genomic DNA from 17 PHP-Ib patients, three recently is olated human genomic DNA clones were further characterized by restrict ion enzyme mapping and nucleotide sequencing across intron/exon border s. Regions including all 14 coding exons and their splice junctions we re amplified by polymerase chain reaction, and the products were analy zed by either temperature gradient gel electrophoresis or direct nucle otide sequencing. Silent polymorphisms were identified in exons G (1 o f 17), M4 (1 of 17), and M7 (15 of 17). Two base changes were found in introns, 1 at the splice-donor site of the intron between exons E2 an d E3 (1 of 17) and the other between exons G and M1 (2 of 17), Total r ibonucleic acid from COS-7 cells expressing minigenes with or without the base change between exons E2 and E3 showed no difference by either Northern blot analysis or reverse transcriptase-polymerase chain reac tion. Radioligand binding was indistinguishable for both transiently e xpressed constructs. A missense mutation (E546 to K546) in the recepto r's cytoplasmic tail (3 of 17) was also found in 1 of 60 healthy indiv iduals, and PTH/PTHrP receptors with this mutation were functionally i ndistinguishable from wild-type receptors. PHP-Ib thus appears to be r arely, if ever, caused by mutations in the coding exons of the PTH/PTH rP receptor gene.