THE GENE RESPONSIBLE FOR PSEUDOHYPOPARATHYROIDISM TYPE IB IS PATERNALLY IMPRINTED AND MAPS IN 4 UNRELATED KINDREDS TO CHROMOSOME 20Q13.3

Hypocalcemia and hyperphosphatemia caused by parathyroid hormone (PTH) -resistance are the only discernible abnormalities in pseudohypoparath yroidism type nb (PHP-Ib). Because mutations in the PTH/PTH-related pe ptide receptor, a plausible candidate gene, had been excluded previous ly, we conducted a genome-wide search with four PHP-Ib, kindreds and e stablished linkage to a small telomeric region on chromosome 20q, whic h contains the stimulatory G protein gene. We, furthermore, showed tha t the genetic defect is imprinted paternally and thus is inherited in the same mode as the PTH-resistant hypocalcemia in kindreds with PHP-I a and/or pseudo-pseudohypoparathyroidism, two related disorders caused by different stimulatory G protein mutations.