– α Crystallin B Chain (CRYAB) is a cytoplasmic protein that belongs to the small heat shock protein (HSP20) family. Alpha crystallins are composed of two gene products: alpha-A and alpha-B, for acidic and basic, respectively. Alpha crystallins can be induced by heat shock and are members of the small heat shock protein (sHSP also known as the HSP20) family. Alpha crystallins acts as molecular chaperones and hold them in in large soluble aggregates. CRYAB is expressed widely in many tissues and organs. It may contribute to the transparency and refractive index of the lens. The deficiency of CRYAB is the cause of myopathy myofibrillar type 2 (MFM2) and cataract posterior polar type 2 (CTPP2).