SIX Homeobox Protein 6 (SIX6)

SIX6 is a homeobox protein that is similar to the Drosophila 'sine oculis' gene product. This gene is found in a cluster of related genes on chromosome 14 and is thought to be involved in eye development. Defects in this gene are a cause of isolated microphthalmia with cataract type 2 (MCOPCT2). SIX6 encodes a predicted 246-amino acid protein. Northern blot analysis detected expression of an approximately 1.5-kb SIX6 transcript only in Jurkat T cells and in the adult eye. RT-PCR analysis detected strong expression of SIX6 in the embryonic eye starting between 12 and 14 weeks of gestation. Genomic analyses in one of these patients demonstrated SIX6 hemizygosity; the authors suggested that SIX6 haploinsufficiency was responsible for the ocular and pituitary phenotype in that patient.