Melanocortin 3 receptor (MC3R) gene variants in extremely obese women

OBJECTIVE: Following several reports of linkage of obesity related phenotyp es to human chromosome 20q we sought to determine whether variations of the melanocortin 3 receptor (MC3R) gene are associated with obesity. DESIGN: We screened the MC3R gene coding region and approximately 2 kb of 5 ' and 3' flanking sequences for DNA variants in unrelated extremely obese w omen and average weight controls using polymerase chain reaction (PCR) sing le strand conformation polymorphism (SSCP) analysis and DNA sequencing. SUBJECTS: 124 unrelated extremely obese women (body mass index, (BMI) great er than or equal to 40 kg/m(2)) and 85 average weight controls (BMI < 27 kg /m(2)). MEASUREMENTS: Radiation hybrid (RH) mapping was performed to localize the M C3R gene. 5' and 3' flanking sequences of MC3R gene were cloned. PCR-SSCP a nd DNA sequencing were used to detect mutations in the MC3R gene coding reg ion and flanking sequences, RESULTS: RH mapping localized the MC3R gene to 20q13, between markers D20S1 00 and D20S149. 1083 bp 5' and 653 bp 3' flanking region of the MC3R gene w ere cloned. A missense mutation ( + 241, codon 81 ATT/GTT, Ile --> Val) was found in the MC3R coding region. Four more variants were detected in the 5 ' flanking sequence: -201(C --> G), -239 (A --> G), -762(A --> T) and -769( T --> C). Compared with controls, no significant allele frequency differenc es were found. Racial differences were found for the + 241, -201, -239 and -762 polymorphisms. CONCLUSIONS: Several sequence variants were found in the MC3R gene coding r egion and in 5' flanking sequences. However, none of the variants were asso ciated with obesity phenotypes. The linkage of extreme human obesity on 20q 13 is likely caused by genes other than MC3R.