Aquaporin 0 or MIP26 (major intrinsic protein 26kD), and Aquaporin 1 has been the foundation of the growing family of aquaporins. The lens specific Aquaporin 0 represents up to 80 % of total lens membrane protein. Defects in Aquaporin 0 are a cause of autosomal recessive congenital cataract. The lens opacity mutation (LOP) is an AA substitution that inhibits targeting of MIP to the cell membrane. Human Aquaporin 0 is a 263 amino acid transmembrane protein belonging to the MIP family. Aquaporin families of proteins are predicted to contain six transmembrane domains.