Objective: Mutations in the pro-opiomelanocortin and melanocortin 4 receptor genes (POMC and MC4R) cause monogenic obesity, and the POMC locus (2p21) has been linked to leptin levels and body mass index (BMI). We searched for monogenic obesity due to mutations in POMC and MC4R among morbidly obese Swedes and studied the association of POMC variants with BMI and serum leptin levels.
Design: MC4R and POMC were screened for mutations in 102 obese Swedish subjects (40+/-11 y, 41.3+/-5.0 kg/m(2)) using the single-strand conformation polymorphism technique. The detected polymorphisms were genotyped in 118 lean control subjects (56+/-11 y, 22.6+/-1.3 kg/m(2)) and studied for association with BMI and serum leptin levels.
Results: No cases of monogenic obesity due to mutations in POMC or MC4R were identified and none of the four common POMC polymorphisms (RsaI, ins56, Glu188Gly and C8246T) were associated with obesity. Lean carriers of the C8246T CC-genotype had higher serum leptin levels compared to CT or TT carriers (9.7+/-6.6 vs 6.7+/-4.4 microg/l, P=0.003 for leptin levels adjusted for age, sex and BMI in regression analysis), especially lean females (P=0.004) and lean female carriers with the C8246T(CC)/RsaI(--or +-) genotype combinations (P<0.0005). Neither the C8246T CC-genotype nor the C8246T(CC)/RsaI(--or +-) were associated with serum leptin levels in obese subjects.
Conclusions: Monogenic forms of obesity due to mutations in POMC and MC4R are rare in Swedish obese patients. Polymorphisms in POMC are associated with variation in serum leptin levels within the normal range in healthy lean but not in obese individuals.