Humans with steroid sulfatase deficiency are at significantly increased risk of developing inattentive subtype ADHD (and possibly autism) relative to the general population (Kent et al., 2008); a number of case studies have also reported ADHD and autistic symptoms in steroid sulfatase-deficient individuals (Thomas et al., 1999, Tobias et al., 2001, Doherty et al., 2003). Here, STS is linked to recessive X-linked ichthyosis.