The gene encoding BCAS4 (Breast carcinoma-amplified sequence 4), a 211 amino acid protein, is found in a region on chromosome 20 that is frequently amplified in human breast cancer. The amplification and translocation between the BCAS4 gene and the BCAS3 gene, with a 17q23 locus, results in a fusion transcript that is overexpressed in MCF-7 cells. Also, deletion of chromosomal region 20q13.13-q13.2 and resultant deletion of BCAS4, as well as three other genes, is the cause of Okihiro syndrome, a disease characterized by ocular and upper limb anomalies.