COMT and diabetic kidney disease: While various studies have implicated genetic variations in COMT and dopamine receptor genes in essential hypertension [29-35], and one study has implicated COMT (based on a functional assay using a COMT inhibitor) in diabetic kidney disease in rats [10], an association of dopaminergic pathway gene polymorphisms with kidney disease among individuals with type-2 diabetes has not been tested in any population so far.