SIX Homeobox 6 (SIX6) is a member of the SIX/Sine oculis homeobox family contains 1 homeobox DNA-binding domain. The SIX6 protein is essential in embryonic development by providing necessary instructions for the formation of the forebrain and eye development. SIX6 is expressed in the developing and adult retina, hypothalamic and the pituitary regions. SIX6 gene defects are the cause of microphthalmia isolated with cataract type 2.