Lines of evidence show a role of the melanocortinergic system in the regulation of glucose metabolism in obese subjects. The aim of this study was to investigate the influence of proopiomelanocortin (POMC) in the variability of insulin levels in early-onset obesity. To address this issue, an association study using a 9-bp insertional polymorphism, AGC AGC GGC, between nucleotides 6979 and 6998 of the POMC gene, was performed in 380 (185 girls) Italian obese children and adolescents. Allelic frequencies were comparable in our patients (0.053) and in 300 lean controls of Mediterranean descent (0.045). Interestingly, we showed that this polymorphism, in the obese patients, was associated with differences in fasting insulin levels; this finding persisted after correction for age, sex, and pubertal stage. Heterozygotes had 24% higher mean insulin levels than those homozygous for the wild allele and showed a stronger correlation between insulin and body mass index (P < 0.001). These findings support the hypothesis that the melanocortin pathway may modulate glucose metabolism in obese subjects and suggest that this common POMC variant may be involved in the natural history of polygenic obesity in late adolescence and adulthood, contributing to the link between type 2 diabetes and obesity.
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