A related pseudogene, CYP21A1P is located near this gene.[24] Both genes are located on chromosome 6, in the major histocompatibility complex III[25] close to the Complement component 4 genes C4A and C4B and Tenascin X gene TNXB,[26] and the pseudogene, CYP21A1P, retains 98% exonic sequence identity with the functional gene CYP21A2.[27]