Mammalian lens crystallins are divided into alpha, beta, and gamma families.  Alpha crystallins consist of two gene products: alpha-A and alpha-B.  Alpha-A is solely expressed in the lens and alpha-B is expressed widely in many tissues.  The gene that codes for the Alpha crystallin A chain is called CRYAA and is located on the long arm of chromosome 21.  Alpha crystallin A is the major protein in the eye, and plays a major role in maintaining the transparency and refractive index of the lens.  In addition, it acts as molecular chaperone, forming soluble aggregates to protect cellular components under conditions of stress, via stabilizing and protecting the lens fiber cells. 

Mutations in the CRYAA gene are implicated in the development of a form of congenital cataract called CTRCT9.

CRYAA is a 3 kb gene located on the long arm of chromosome 21.  It contains three exons and codes for the CRYAA (Alpha Crystallin A Chain) protein.  The protein consists of 173 amino acids, and has a size of 19 kDa.  In the mature alpha crystallin protein, three of these A chains associate with one of the B chains to form a heteropolymer.  The CRYAA protein contains a conserved alpha-crystallin domain, flanked on either side by a hydrophobic N-terminal domain, and a hydrophilic unstructured C-terminal.