FGF21 and idiopathic pulmonary arterial hypertension: Circulating levels of the predominantly adipose tissue-derived cytokines FABP-4 (p = 0.0107), FGF-21 (p = 0.0013), and adiponectin (p = 0.0021) were significantly increased in the serum of patients with IPAH, compared to the normal control group (Figure 1).