OGT and Klinefelter syndrome: Interestingly, the human OGT gene is located on the Xq13 near the Xist locus, so that TS subjects with isochromosomes Xq have two OGT alleles on the same X chromosome, and thus, they could potentially overexpress OGT. In support of this hypothesis, an increased risk for T2DM has been observed among patients with Klinefelter syndrome (47,XXY) and 48,XXYY who have supernumerary copies of OGT, even in the absence of X-monosomy [123–125].