SPATA9 is a 254 amino acid single-pass membrane protein that is highly expressed in testis and pancreas with low expression in heart, lung, and brain. A component of the sperm acrosome, SPATA9 may participate in sperm capacitation and acrosome reaction, and is therefore necessary for fertilization. SPATA9 is also suggested to be involved in testicular development/spermatogenesis and may be an important factor in male infertility. No expression of SPATA9 was found in patients affected by Sertoli-cell-only syndrome, also known as Del Castillo syndrome or germ cell aplasia, which is characterized by male sterility without sexual abnormality. SPATA9 is encoded by a gene located on human chromosome 5, which consists of about 181 million base pairs, encodes around 1,000 genes and represents about 6% of human genomic DNA.