The CD38 mutation that caused tryptophan to replace arginine at amino acid residue 140 (R140W; [rs1800561, 4693C > T]) [29] was found not only in Japanese type 2 diabetes patients but also in 0.6–4.6% of the Japanese population and was associated with autism spectrum disorder in a smaller case-control study [92]. Here, CD38 is linked to type 2 diabetes mellitus.