Identification and functional characterization of a missense mutation in resistin in two patients with severe obesity and insulin resistance

Objective: In this study, we hypothesized that mutations in the resistin encoding gene, RETN ,m ay cause a monogenic form of obesity. Design/methods: We screened the coding region of RETN in 81 morbidly obese adults, 263 overweight and obese children/adolescents, and 116 healthy lean subjects. In vitro experiments include qPCR, ELISA, and western blot for WT and mutant resistin transfected into 3T3-L1 adipocytes. Results: Mutation analysis identified five sequence variants in our patient populations: 3 0 -UTR C87 G/A, 3 0 -UTR C100 A/G, T73T, IV3-61 C/A, and C78S. In our control population, we only found the 3 0 -UTR C87 G/A variant. We started functional experiments for the C78S mutation that was found in a 20-year-old obese male (body mass index (BMI)Z39.7 kg/m 2 ) and his obese mother (BMIZ31.9 kg/m 2 ). In vitro testing demonstrated that the mutation does not impair mRNA expression. We identified a 100-fold lower extracellular protein concentration for mutant resistin compared with WT levels using a resistin ELISA on cell culture medium (PZ4.87!10 K6 ). We also detected a decreased intracellular concentration for the mutant protein (tenfold lower relative levels, PZ0.007). The plasma resistin levels of the proband and his mother, however, did not differ significantly from lean control individuals. Conclusions: In conclusion, we identified the first missense mutation in resistin in a morbidly obese proband and his obese mother. Functional testing of the mutant protein suggests that the C78S mutant protein is degraded, possibly resulting in a decreased extracellular concentration, which may predispose to obesity.