PRTN3 and obesity due to melanocortin 4 receptor deficiency: For example, smoking is a well-established risk factor for anti-citrullinated-protein antibody (ACPA)-positive RA.17 Obesity is a well-known risk factor for gout,18 psoriasis19 and PsA.20 If obesity and other components associated with MetS are more common in some IJDs, it can provide support for a pathophysiological connection between obesity/MetS and these diseases.