TACR1 and attention deficit-hyperactivity disorder: Our proposal that NK1R−/− mice can be used to study the behavioural and cognitive abnormalities seen in ADHD patients is supported by evidence from translational studies, which discovered that an association between polymorphisms in, or near, the human equivalent of the NK1 receptor gene (TACR1) predicts increased vulnerability to ADHD (Sharp et al., 2009; 2014; Yan et al., 2010).