[Pseudohypoparathyroidism type I b and genomic imprinting]

Pseudohypoparathyroidism type I b is characterized by unresponsiveness solely to parathyroid hormone in contrast to pseudohypoparathyroidism type I a which induces resistance to several hormones. Abnormal imprinting of GNAS gene which encodes Gsalpha protein is considered to be responsible for pseudohypoparathyroidism type Ib. Actually, several deletions were reported in the upstream region of GNAS gene. These deletions are considered to cause reduced expression of Gsalpha protein in renal proximal tubules. However, the detailed mechanism how these deletions cause abnormal imprinting of GNAS gene remains to be elucidated. Analysis of pathogenesis of pseudohypoparathyroidism type Ib should contribute to the understanding of regulatory mechanisms of gene expression.