haplotype, present in all populations [H2 is found predominately in those of European ancestry (Stefansson et al. 2005)], is associated with increased risk for PSP and other neurologic disorders (Pastor et al. 2004; Skipper et al. 2004; Cruts et al. 2005; Pittman et al. 2006; Sundar et al. 2007; Webb et al. 2008). Evidence of positive selection for the H2 haplotype was observed in a large Icelandic sample (Stefansson et al. 2005); however, a predisposition to a microdeletion syndrome resulting in mental retardation and neurologic symptoms has also been associated with the H2 haplotype (Koolen et al. 2006).
