Whereas BDNF levels were reduced in the subgroup of patients with PAH (922.8±235.6 vs 1135.8±145.4 pg/mL in the absence of PAH, p = 0.05); patients with grade II, III and IV PAH had similar BDNF decreased serum levels (893.9, 898 and 1130 pg/mL, respectively). This evidence concerns the gene BDNF and pulmonary arterial hypertension.