Fig. (2).

Schematic diagram of the human thiopurine methyltransferase gene and its common mutant alleles. The gene is located in the short arm of the chromosome 6 and is comprised of 10 exons. Mutations of the common alleles are located in the V, VII and X exons. Gray rectangles represent exons that contain mutations. White rectangles are untranslated regions and black rectangles represent exons in the open reading frame.