PAK3 and X-linked intellectual disability: 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).