KIF21B and attention deficit-hyperactivity disorder: For example, the rare variant analysis identified KIF21B (Asselin et al., 2020), which has been associated with smoking initiation (Saunders et al., 2022), ADHD (Cross-Disorder Group of the Psychiatric Genomics Consortium, 2013), and schizophrenia (Trubetskoy et al., 2022).