Simpson et al15 reported median levels of 2.24 pg/mL (interquartile range, 1.09 to 4.33 pg/mL) in connective tissue disease associated PAH and 1.62 pg/mL (interquartile range, 0.72 to 2.94 pg/mL) in idiopathic PAH, which implies that IL-6 levels are disease- and genotype-specific. This evidence concerns the gene IL6 and connective tissue disorder.