The genetic contribution to common obesity has been established through family, twin, and adoption studies. Twin studies have shown that genetic factors may contribute to >40% of the variation in BMI while lower heritability has been shown in families (>20%) and adoption (>20%), respectively [7, 8, 14, 15]. Yet, despite a relatively high heritability, the search for obesity susceptibility genes has been an arduous task. Progress until recently has been slow and success limited. Although recent success of genome-wide association studies has drawn a lot of attention, gene identification for the last 15 years has been based on two broad genetic epidemiological approaches, that is, candidate gene and genome-wide linkage methods.
