The incidence of type 2 diabetes is rising rapidly worldwide, and there are already more than 180 million diabetic subjects. Type 2 diabetes risk factors include ethnic background, age, hypertension, overweight, increased abdominal fat and lack of physical exercise. Obesity is considered to be the most important risk factor for type 2 diabetes and the main factor driving the current epidemic, as 90% of type 2 diabetes patients are obese. Worldwide, obesity has also reached epidemic proportions, with 300 million adults classified as clinically obese (based on data from the World Health Organization). Up to 50% of these obese individuals will develop type 2 diabetes at some stage in their life, depending on the age at which they became obese.

Type 2 diabetes and obesity are multifactorial disorders in which both genetic and non-genetic (environmental and lifestyle) factors play a role. Although the lifetime risk for type 2 diabetes in the western world is around 10%, first-degree relatives of patients have a 20–40% risk of the disease, and concordance rates for identical twins have been estimated to be 57% or higher (up to 90%) for type 2 diabetes in male twins.1 These observations clearly indicate that there is a genetic component to the disease. However, the model seems to be more complex, involving multiple genes and environmental factors.

Common obesity and type 2 diabetes share some non-genetic factors, as both are influenced by diet and physical inactivity. Both conditions are characterised by insulin resistance, suggesting a shared pathology. It has been proposed that susceptibility to developing type 2 diabetes and obesity is, in part, due to shared underlying genetic factors involved in common molecular mechanisms. This article explores the genes recently identified for type 2 diabetes and obesity by genome-wide association studies (GWAS) and evaluates their functions in an effort to determine whether there is any support for the hypothesis that type 2 diabetes and obesity share some underlying mechanism(s).

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