HAP1 and Huntington disease: These authors also found that a number of proteins that have been shown to be upregulated in striatal neurons isolated from YAC128 mice—such as huntingtin associated protein 1 (Hap1), calretinin (Calb2) and anterior pharynx defective 1 homolog isoform b (Aph1b)—remained at the same expression level in HD PC12 cells as in control cells.