Human CYP2D6*13 allele, located in the vicinity of 22q13.1, is a variant form of the CYP2D6 wild-type allele and encodes cytochrome P450 2D6*13 protein. The CYP2D6*13 allele, resulting from large deletions (approximately 20 kb) in the CYP2D gene cluster, is a hybrid consisting of exon 1 of the CYP2D7 gene and exons 2-9 of the CYP2D6 gene. CYP2D6*13 allele exhibits an insertion in exon 1 which causes a reading frame shift. This alteration yields a truncated cytochrome P450 2D6*13 protein that is enzymatically inactive. [ ]