Importantly, variation in TCF7L2 was previously associated with T2D risk and is the strongest genetic determinant for T2D in human populations [29], [30], [31], Given these genetic associations, TCF7L2 could serve as a key regulator of both glucose homeostasis and behavior and consequently represents an ideal candidate for interrogating the potential role of common genetic underpinnings in the comorbidity between T2D and psychiatric disorders. Here, TCF7L2 is linked to type 2 diabetes mellitus.