HAP1 and Huntington disease: To identify genes with potential significance in this HD animal model, we focused on genes whose expression was changed at least 1.5-fold in the striatum; namely, Hap1 (huntingtin-associated protein 1), Calb2 (calretinin), Aph1 (anterior pharynx defective 1 homolog) isoforms a, b and c, Psenen (presenilin enhancer 2 homolog), Psen2 (presenilin 2), Cib1 (calmyrin 1), CacyBP/SIP (calcyclin-binding protein), Calr (calreticulin), and Cib2 (calmyrin 2).