Studying brain tissue is particularly challenging because these tissue samples have to be collected post-mortem and there is a high degree of cellular heterogeneity. Although some eQTLs have been nominated for brain diseases, such as MAPT in Parkinson's disease (PD) and progressive supranuclear palsy (PSP) (Hoglinger et al., 2011, Nalls et al., 2011b, Tobin et al., 2008, Vandrovcova et al., 2010), many nominated loci for brain phenotypes are not functionally annotated.
