In a total of 398 subjects, Smith et al. [30] evaluated a set of 164 single-nucleotide polymorphisms (SNPs) from 31 candidate genes and found that two SNPs in the ciliary neurotrophic factor receptor (CNTFR) were associated with the severity of ADHD inattentive symptom. This evidence concerns the gene CNTFR and attention deficit-hyperactivity disorder.