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, may 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'-UTR +87 G/A, 3'-UTR +100 A/G, T73T, IV3-61 C/A, and C78S. In our control population, we only found the 3'-UTR +87 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)=39.7 kg/m(2)) and his obese mother (BMI=31.9 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 (P=4.87×10(-6)). We also detected a decreased intracellular concentration for the mutant protein (tenfold lower relative levels, P=0.007). 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.