Based on work in mouse models, the STS gene (which encodes the enzyme steroid sulfatase) was proposed as a novel ADHD candidate (Davies et al., 2007); in mice Sts is located within the pseudoautosomal region of the sex chromosomes, whereas its human orthologue resides within the X-specific region at Xp22.3. This evidence concerns the gene STS and attention deficit-hyperactivity disorder.