These results are consistent with findings of Toledo-Rodriguez et al. that prenatal exposure to ETS (which contains PAH) was associated with increased methylation of the BDNF exon and down-regulation of BDNF[33], and reports of dysfunction in the BDNF system and compromised cognitive function in adult life from fetal exposure to unfavorable intrauterine conditions [34]. Here, BDNF is linked to pulmonary arterial hypertension.