 Subsequently, the STSL locus has been further localized to a less than 2 centimorgans (cM) region.In 2001, The STSL locus was found to be comprises two genes, ABCG5 and ABCG8, encoding 2 members of the ABC-transporter family, named sterolin-1 and sterolin-2, respectively, Sterolin-2, discovered after sterolin-1, is located <400 base pair (bp) upstream of sterolin-1 in the opposite orientation.Typical ABC transporter consists of two transmembrane domains and two nucleotide-binding domains.