Background: Common single-nucleotide polymorphism (SNP) variants around the melanocortin 4 receptor (MC4R) gene have recently been associated with obesity risk and insulin resistance. Obesity is a known risk factor for colorectal cancer (CRC) and we hypothesized that there might be a common inherited genetic component.
Methods and results: Four of the variants reported earlier were genotyped and tested for association with body mass index (BMI), waist circumference (WC), dietary energy intake (DEI) and CRC. Using a case-control genetic association study, we replicated the association with BMI (P=0.0001, additive genetic effect=0.37 kg/m(2)) and WC (P=0.005, additive genetic effect=0.70 cm) using over 3800 individuals. However, there was no association between these variants and CRC risk. Rare (highly penetrant) variants within the MC4R gene have been shown to influence eating behaviour and hyperphagia. We hypothesized that the newly identified common variants might also influence hyperphagia. Using DEI data recorded from a validated food frequency questionnaire, we found no significant genetic association between MC4R SNPs and DEI.
Conclusions: As the MC4R locus explains only 0.28% of the BMI and 0.14% of the WC phenotypic variance in the Scottish population, most of the genetic contribution to obesity remains to be identified.