In Reply We agree with Fluegge that environmental factors may modulate brain-derived neurotrophic factor (BDNF) levels in children with autism spectrum disorder because Fluegge pointed out that the levels of BDNF were regulated by nitrous oxide mimics and opioid exposure in animals. Furthermore, exposure of valproic acid in pregnant rats and mice is wildly used as an animal model of autism. Almeida et al1 reported that exposure of valproic acid dramatically increased both BDNF messenger RNA and BDNF protein levels in the fetal mouse brain,1 which is consistent with Fluegge’s hypothesis.