Peripheral brain-derived neurotrophic factor in autism spectrum disorder: a systematic review and meta-analysis

Brain-derived neurotrophic factor (BDNF) regulates neuronal survival and growth and promotes synaptic plasticity. Recently, researchers have begun to explore the relationship between peripheral BDNF levels and autism spectrum disorder (ASD), but the findings are inconsistent. We undertook the first systematic review and meta-analysis of studies examining peripheral BDNF levels in ASD compared with healthy controls. The PubMed, Embase, and Cochrane Library databases were searched for studies published before February 2016. Fourteen studies involving 2,707 participants and 1,131 incident cases were included. The meta-analysis provided evidence of higher peripheral BDNF levels in ASD compared with controls [standardized mean difference (SMD) = 0.63, 95% confidence interval (95% CI) = 0.18-1.08; P = 0.006]. Subgroup analyses revealed higher BDNF levels in ASD compared with controls for both serum [SMD = 0.58, 95% CI = 0.11-1.04; P = 0.02] and plasma [SMD = 1.27, 95% CI = 0.92-1.61; P < 0.001]. Studies of childhood yielded similar cumulative effect size [SMD = 0.78, 95% CI = 0.31-1.26; P = 0.001], while this was not true for the studies of adulthood [SMD = 0.04, 95% CI = -1.72-1.80; P = 0.97]. This meta-analysis suggests that peripheral BDNF levels are a potential biomarker of ASD.