Estrogen-related receptor alpha (ERRα), also known as NR3B1 (nuclear receptor subfamily 3, group B, member 1), is a nuclear receptor that in humans is encoded by the ESRRA (Estrogen Related Receptor Alpha) gene.[5][6] ERRα was originally cloned by DNA sequence homology to the estrogen receptor alpha (ERα, NR3A1),[6] but subsequent ligand binding and reporter-gene transfection experiments demonstrated that estrogens did not regulate ERRα.[7] Currently, ERRα is considered an orphan nuclear receptor.[6][7]