GRAP and Huntington disease: Furthermore, of the 12 overlapping genes, the four genes (POP5, GRAP, USP5, and SEC24C) showing an expected inverse correlation between methylation and RNA expression levels are involved in RNA metabolism, the innate immune response, ubiquitination, and intracellular protein transport and antigen presentation, respectively, also supporting their involvement in systemic response to HD, however, they have not been previously linked with HD and none of them achieved FDR < 0.05 in the case of differential methylation.