PRTN3 and obesity due to melanocortin 4 receptor deficiency: Our study highlights that obesity has a different effect on the disease course of ACPA-positive and ACPA-negative RA patients, which may further support the hypothesis that ACPA-positive and ACPA-negative disease are different subsets of the disease or even different entities (in line with a recently suggested differentiation in type 1 and 2 RA) [8].