Admixture mapping of 15,280 African Americans has identified three loci, 5q13,3, Xq13.1, and Xq25, that may harbor genetic variants associated with variations in BMI [51]. The 95% confidence interval (CI) for the chromosome 5 peak contains CART gene. Only a few studies report linkage of obesity with markers on the X chromosome. Three studies reported either suggestive or significant linkage of obesity to the q arm of chromosome X [52–54] and they all mapped to the Xq23-q24 region, which overlaps with the 95% CI of the highest admixture peak on chromosome X in this study. The 95% CI in this study contains one particular gene that may be a candidate for obesity susceptibility. The gene solute carrier family 6 member 14 (SLC6A14) is involved in serotonin synthesis and serotonergic receptor mechanisms that have been implicated in appetite control and body weight regulation [55]. Another potential candidate gene near the highest admixture peak is the cullin 4B (CUL4B) gene. CUL4B was recently identified as a causative gene for an X-linked mental retardation syndrome, which was associated with several clinical features, including central obesity [56].
