The protein coded by ARHGAP10 is a member of the Rho GTPase activating protein (Rho-GAP) family which are negative regulators of Rho-GTPase signaling pathways related to actin cytoskeleton dynamics, cell proliferation, and differentiation (Basseres et al., 2002). The fact that this gene is highly expressed in muscle and brain further supports the hypothesis that ARHGAP10 is important for cell differentiation and might be implicated in neuronal plasticity (Basseres et al., 2002). KIAA1409 has not been extensively studied, but is believed to form part of a cation channel activated by neuropeptides substance P or neurotensin. MARK1 is a member of the MARK family of protein kinases and plays a key role in phosphorylation of microtubules involved in dendritic growth. Variants have been associated with autism spectrum disorders (ASDs) and over-expression of MARK1 in the prefrontal cortex of post-mortem brain tissue of patients with ASDs has been reported (Maussion et al., 2008). DDX6 lies at 121 cM on chromosome 11; this locus may harbor genes associated with smoking-related behavior (Li et al., 2008). We have previously found suggestive linkage for DSM-IV defined
