Diaz-Hernandez et al. found that the catalytic activity of the 20S core was preserved in HD mouse model brain extracts, and there was induction of immunoproteasome subunits LMP2 and LMP7 in the cortex and striatum of human brains and mouse models, with immunohistochemistry showing the highest expression in neurons. Here, PSMB9 is linked to Huntington disease.