Members of these families are implicated in cognitive defects in humans, since the genes for the GEF αPIX (ARHGEF6) and PAK3 (PAK3) are mutated in patients with X-linked intellectual disability (Allen et al., 1998; Kutsche et al., 2000), while the gene for GIT1 (GIT1) is altered in patients with attention deficit hyperactivity disorder (ADHD) (Won et al., 2011). Here, PAK3 is linked to attention deficit-hyperactivity disorder.