The only well-defined mutation that involves RARs is a reciprocal translocation that occurs between the RARα (human chromosome 17) and the promyelocytic leukemia (human chromosome 15) loci in some forms of acute promyelocytic leukemia (APL) (de The et al. 1991; Kakizuka et al. 1991). This evidence concerns the gene RARS1 and acute promyelocytic leukemia.