Nephrogenic diabetes insipidus.
Nephrogenic diabetes insipidus, which can be inherited or acquired, is characterized by an inability to concentrate urine despite normal or elevated plasma concentrations of the antidiuretic hormone arginine vasopressin. Polyuria, with hyposthenuria, and polydipsia are the cardinal clinical manifestations of the disease. About 90% of patients with congenital nephrogenic diabetes insipidus are males with the X-linked recessive form of the disease (OMIM 304800) who have mutations in the arginine vasopressin receptor 2 gene (AVPR2), which codes for the vasopressin V2 receptor. The gene is located in chromosomal region Xq28. In <10% of the families studied, congenital nephrogenic diabetes insipidus has an autosomal-recessive or autosomal-dominant (OMIM 222000 and 125800, respectively) mode of inheritance. Mutations have been identified in the aquaporin-2 gene (AQP2), which is located in chromosome region 12q13 and codes for the vasopressin-sensitive water channel. When studied in vitro, most AVPR2 mutations result in receptors that are trapped intracellularly and are unable to reach the plasma membrane. A few mutant receptors reach the cell surface but are unable to bind arginine vasopressin or to properly trigger an intracellular cyclic AMP signal. Similarly, aquaporin-2 mutant proteins are misrouted and cannot be expressed at the luminal membrane. Chemical or pharmacological chaperones have been found to reverse the intracellular retention of aquaporin-2 and arginine vasopressin receptor 2 mutant proteins. Because many hereditary diseases stem from the intracellular retention of otherwise functional proteins, this mechanism may offer a new therapeutic approach to the treatment of those diseases that result from errors in protein kinesis.