homozygous for inactivating mutations in the aquaporin-0 gene develop congenital cataracts. A small number of people have been identified with severe or total deficiency in aquaporin-1. They are, in general, healthy, but exhibit a defect in the ability to concentrate solutes in the urine and to conserve water when deprived of drinking water. Mice with targeted deletions in aquaporin-1 also exhibit a deficiency in water conservation due to an inability to concentrate solutes in the kidney medulla by countercurrent multiplication. In addition to its role in genetically determined nephrogenic diabetes insipidus, aquaporins also play a key role in acquired forms of nephrogenic diabetes insipidus (disorders that cause increased urine production). Aquaporin 2 is regulated by vasopressin which, when bound to the cell-surface receptor, activates the cAMP signaling pathway. This results in aquaporin-2 containing vesicles to increase water uptake and return to circulation. Mutation of the aquaporin 2 vasopressin receptor is a cause of acquired diabetes insipidus. In rats, acquired nephrogenic diabetes insipidus can be caused impaired regulation of aquaporin-2 due to administration of lithium salts, low potassium concentrations in the blood (hypokalemia) and high calcium concentrations in the blood (hypercalcemia). Autoimmune reactions against aquaporin 4 in humans produce Devic's disease. If aquaporin could be manipulated, that could potentially solve medical problems such as fluid retention in heart disease and brain edema after stroke. Additional indication suggested aquaporin 4 is involved in human disease when it is disturbed. The U.S. Food and Drug Administration today approved Soliris (eculizumab) injection for intravenous use for the treatment of neuromyelitis optica spectrum disorder (NMOSD) in adult patients who are anti-aquaporin-4 (AQP4) antibody positive. NMOSD is an autoimmune disease of the central nervous system that mainly affects the optic nerves and spinal cord. References External links Animation (MPEG file at nobel.se) Integral membrane proteins Biology of bipolar disorder