Several genetic modifiers of HD have been identified so far, including huntingtin-associated protein-1 (HAP1) [6], ubiquitin C-terminal hydrolase 1 (UCHL1) [7,8], GluR6 subunit of kainate receptor (GRIK2) [9], the adenosinergic A2A receptor (ADORA2A)[10,11], autophagy-related protein 7 (Atg7) [12] and the peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) [13-15]. The gene discussed is HAP1; the disease is Huntington disease.