Only four proteins remained after the sequential filtering that could possibly play key roles in linking HD and UPR, and can be targeted with existing drugs: histone deacetylase1 (HDAC1), jun proto-oncogene (JUN), solute carrier family 25 member 4 (SLC25A4) and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) (Fig. 5d). Here, HMGCR is linked to Huntington disease.