Cytogenetic deletions on the short arm of the X chromosome encompassing the steroid sulfatase (STS) gene have been noted in cases of neurodevelopmental disorders associated with abnormal cognition, including attention deficit hyperactivity disorder (ADHD) (Doherty et al. 2003; Lonardo et al. 2007; Tobias et al. 2001), schizophrenia (Milunsky et al. 1999) and autism (Shinawi et al. 2009; Thomas et al. 1999; Vorstman et al. 2006). The gene discussed is STS; the disease is attention deficit-hyperactivity disorder.