MUTATIONS IN THE VASOPRESSIN V2 RECEPTOR GENE IN FAMILIES WITH NEPHROGENIC DIABETES-INSIPIDUS AND FUNCTIONAL EXPRESSION OF THE Q-2 MUTANT

Nephrogenic diabetes insipidus (NDI) is characterized by a resistance of the kidney towards arginine vasopressin (AVP). Following molecular cloning of the vasopressin V2 receptor, we identified different mutati ons in the V2 receptor gene in families with X-linked NDI, which segre gated with the disease. The Hopewell mutation (W71X) causes the diseas e in the largest North American NDI pedigree, with most of its members residing on Nova Scotia. Different mutations were found in three fami lies from the Quebec area (Q-2: R137H, Q-3: R113W, Q-5: 804delG) and i n the large Cannon kindred residing in Utah (L312X). In an Iranian fam ily (O-1), another mutation was detected (A132D). Three of the six mut ations (Hopewell, Cannon, Q-5) are predicted to cause the expression o f a truncated V2 receptor and are therefore unlikely to function. The functional consequences of missense mutations (Q-2, Q-3, O-1) are less obvious. We therefore introduced the Q-2 mutation into wild-type cDNA . When expressed in COS M6 or Ltk(-) cells, the Q-2 mutant bound AVP w ith normal affinity. However, cells expressing the Q-2 mutant failed t o respond to AVP with an increase in adenylyl cyclase activity. Thus t he Q-2 mutant is unable to interact with or to activate the stimulator y G-protein G(s). The present data indicate that X-linked NDI is frequ ently attributable to a mutation in the V2 receptor gene. In addition, the data prove biochemically that the Q-2 mutation is the cause of ND I in the Q-2 family.