Insulin and IGF2 (11p15.5) are candidate genes for complex traits, including type I diabetes mellitus (T1DM) (Owerbach and Gabbay, 1994), type II diabetes mellitus (T2DM) (Huxtable et al., 2000) and obesity with onset especially in childhood and middle-age (O'Dell et al., 1999; Le Stunff et al., 2001; Gu et al., 2002; Roth et al., 2002; Heude et al., 2004). This evidence concerns the gene IGF2 and obesity due to melanocortin 4 receptor deficiency.