Given that SOCS1 is often dysregulated in a wide variety of liver diseases, and that reduced insulin sensitivity and higher body mass index (BMI) are associated with genetic variants in the SOCS1 gene, we examined the polymorphism in the promoter region of the SOCS1 gene (position −1656; rs243330) for association with obesity and NAFLD-related serum quantitative traits. This evidence concerns the gene SOCS1 and obesity due to melanocortin 4 receptor deficiency.