Objective: The melanocortin-4 receptor (MC4R) regulates energy intake. On the basis of animal studies, it may also regulate energy expenditure.
Research methods and procedures: The effect of the Val103Ile polymorphism of the MC4R gene on energy metabolism was studied in 229 middle-aged nondiabetic subjects (Group 1, age 51.2 +/- 9.8 years, BMI 26.8 +/- 4.5 kg/m2) and on weight gain in 1013 elderly subjects (Group 2, age 69.9 +/- 2.9 years, BMI 27.4 +/- 4.1 kg/m2) during a 3.5-year follow-up study. In Group 1, insulin sensitivity, energy expenditure, and substrate oxidation were measured with the hyperinsulinemic euglycemic clamp combined with indirect calorimetry.
Results: In Group 1, the Val103Ile genotype was associated with high rates of energy expenditure (63.42 +/- 13.40 in eight subjects with the Val103Ile genotype vs. 59.86 +/- 7.33 J/kg per minute in 221 subjects with the Val103Val genotype, p = 0.007), high rates of glucose oxidation (8.90 +/- 6.15 vs. 6.07 +/- 4.38 micromol/kg per minute, p = 0.020), and low levels of free fatty acids (0.45 +/- 0.18 vs. 0.56 +/- 0.23 mM, p = 0.029) in the fasting state, and with high rates of glucose oxidation during the clamp (18.88 +/- 4.63 vs. 17.60 +/- 3.24 micromol/kg per minute, p = 0.031). In Group 2, the 103Ile allele was associated with an increase in weight gain during the follow-up (0.78 +/- 3.98 vs. -0.82 +/- 3.98 kg, p = 0.038).
Discussion: The Val103Ile polymorphism of the MC4R gene is associated with energy expenditure in humans. Furthermore, it may associate with glucose oxidation, free fatty acid levels, and weight gain.
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