Quantitative human glycaemic and obesity-related traits, including fasting plasma glucose and insulin (FG and FI), body mass index (BMI), and waist-hip ratio (WHR) are highly heritable [1–5], and are well established risk factors for type 2 diabetes (T2D) and cardiovascular disease [6–10]. The gene discussed is INS; the disease is obesity due to melanocortin 4 receptor deficiency.