Functional Characterization of the Molecular Defects Causing Nephrogenic Diabetes Insipidus in Eight Families¹

Abstract

X-Linked nephrogenic diabetes insipidus (NDI) is a rare inherited disorder characterized by the excretion of abnormal large volumes of diluted urine mainly caused by mutations in the V2 vasopressin receptor (AVPR2) gene. By screening NDI patients for mutations within the AVPR2 gene we have identified three novel (I46K, F105V, I130F) and four recurrent (D85N, R106C, R113W, Q225X) mutations. In addition, a recurrent missense mutation (A147T) within the aquaporin-2 gene was identified in a female patient with autosomal recessive NDI associated with sensorineural deafness. Selected clinical data of the NDI patients were compared with the results from the in vitro studies. Functional analysis of I46K and I130F revealed reduced maximum agonist-induced cAMP responses as a result of an improper cell surface targeting. In contrast, the F105V mutation is delivered to the cell surface and displayed an unchanged maximum cAMP response, but impaired ligand binding abilities of F105V were reflected in a shifted concentration-response curve toward higher vasopressin concentrations. As the extracellularly located F105 is highly conserved among the vasopressin/oxytocin receptor family, functional analysis of this residue implicates an important role in high affinity agonist binding.

Association of Calnexin with Wild Type and Mutant AVPR2 that Cause Nephrogenic Diabetes Insipidus

“…Although several mutations lead to compromise AVP binding in most cases this results from lack of cell surface expression of the receptor. In the few cases where binding deficient mutant receptors were targeted to the cell surface, a decrease in the affinity for AVP rather than a total loss of binding has generally been observed (4,8,9,12,16,25,36). Besides S315R, the only other mutations for which total loss of detectable binding were reported are W99R (18), R202C, and G185C (52).…”