BDNF and attention deficit-hyperactivity disorder: Although the study of a pedigree with several affected individuals failed to identify causal rare variants for ADHD (Lyon et al., 2011), rare de novo missense variants were found in brain-expressed genes in children with sporadic ADHD (Kim et al., 2017) and novel putative functional rare variants in the BDNF were identified in children and adolescents with ADHD (Hawi et al., 2017).