The AQP2 gene provides instructions for making a protein called aquaporin 2. This protein forms a channel that carries water molecules across cell membranes. It is found in the kidneys in structures called collecting ducts, which are a series of small tubes that reabsorb water from the kidneys into the bloodstream.
The aquaporin 2 water channel plays an essential role in maintaining the body's water balance. The placement of these channels is controlled by a hormone called vasopressin or antidiuretic hormone (ADH). When a person's fluid intake is low or when a lot of fluid is lost (for example, through sweating), the body produces more ADH. This hormone triggers chemical reactions that ultimately insert aquaporin 2 water channels into the membrane of collecting duct cells. These channels allow water to be reabsorbed into the bloodstream, which makes the urine more concentrated. When fluid intake is adequate, less ADH is produced. Without signals from ADH, aquaporin 2 water channels are removed from the membrane of collecting duct cells. At these times, less water is reabsorbed into the bloodstream and the urine is more dilute.
Health Conditions Related to Genetic Changes
Nephrogenic diabetes insipidus
At least 40 mutations in the AQP2 gene have been identified in people with nephrogenic diabetes insipidus.
Most of the known AQP2 gene mutations cause the aquaporin 2 protein to be misfolded into an incorrect 3-dimensional shape. The misfolded protein is trapped within the cell, where it is unable to reach the cell membrane to transport water molecules. A few mutations result in the production of functional aquaporin 2 water channels, but these channels are misrouted within the cell and do not reach the cell membrane.
If aquaporin 2 water channels are not inserted into the membrane of collecting duct cells, the kidneys are unable to respond to signals from ADH. As a result, collecting ducts do not reabsorb water as they should, and the body makes excessive amounts of urine. These problems with water balance are characteristic of nephrogenic diabetes insipidus.More About This Health Condition
Other Names for This Gene
- ADH water channel
- aquaporin 2 (collecting duct)
- collecting duct water channel protein
- water channel protein for renal collecting duct
- water-channel aquaporin 2
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
Catalog of Genes and Diseases from OMIM
- Deen PM, Verdijk MA, Knoers NV, Wieringa B, Monnens LA, van Os CH, van Oost BA. Requirement of human renal water channel aquaporin-2 for vasopressin-dependent concentration of urine. Science. 1994 Apr 1;264(5155):92-5. Citation on PubMed
- Knoers NV, Deen PM. Molecular and cellular defects in nephrogenic diabetes insipidus. Pediatr Nephrol. 2001 Dec;16(12):1146-52. Review. Citation on PubMed
- Kuwahara M, Iwai K, Ooeda T, Igarashi T, Ogawa E, Katsushima Y, Shinbo I, Uchida S, Terada Y, Arthus MF, Lonergan M, Fujiwara TM, Bichet DG, Marumo F, Sasaki S. Three families with autosomal dominant nephrogenic diabetes insipidus caused by aquaporin-2 mutations in the C-terminus. Am J Hum Genet. 2001 Oct;69(4):738-48. Epub 2001 Aug 30. Citation on PubMed or Free article on PubMed Central
- Loonen AJ, Knoers NV, van Os CH, Deen PM. Aquaporin 2 mutations in nephrogenic diabetes insipidus. Semin Nephrol. 2008 May;28(3):252-65. doi: 10.1016/j.semnephrol.2008.03.006. Review. Citation on PubMed
- Marr N, Bichet DG, Hoefs S, Savelkoul PJ, Konings IB, De Mattia F, Graat MP, Arthus MF, Lonergan M, Fujiwara TM, Knoers NV, Landau D, Balfe WJ, Oksche A, Rosenthal W, Müller D, Van Os CH, Deen PM. Cell-biologic and functional analyses of five new Aquaporin-2 missense mutations that cause recessive nephrogenic diabetes insipidus. J Am Soc Nephrol. 2002 Sep;13(9):2267-77. Citation on PubMed
- Noda Y, Sohara E, Ohta E, Sasaki S. Aquaporins in kidney pathophysiology. Nat Rev Nephrol. 2010 Mar;6(3):168-78. doi: 10.1038/nrneph.2009.231. Epub 2010 Jan 26. Review. Citation on PubMed
- Robben JH, Knoers NV, Deen PM. Cell biological aspects of the vasopressin type-2 receptor and aquaporin 2 water channel in nephrogenic diabetes insipidus. Am J Physiol Renal Physiol. 2006 Aug;291(2):F257-70. Review. Citation on PubMed