SLC6A3 and attention deficit-hyperactivity disorder: The link between compulsive behavior and rigid choice pattern has also been shown by a novel animal model of ADHD (Leo et al., 2018); thus, when a strain of dopamine transporter (DAT)-knockout (KO) was compared with DAT heterozygous (HET) and wild-type (WT) rats on an intolerance-to-delay task (IDT), KO rats reacted to the increasing delay with motor stereotypies such as sniffing or chewing the feeding storage area (Cinque et al., 2018).