Finally, there is some evidence that sex differences matter. Four groups report differences in linkage results when the analysis incorporates sex as a covariate. As predicted by the twin results summarized earlier, some loci appear to be sex specific (Abkevich et al., 2003, Camp et al., 2005, Holmans et al., 2007, McGuffin et al., 2005, Zubenko et al., 2003).
