Although this finding was anticipated, as β-hexosaminidase deficiency is pathognomonic in GM2 gangliosidosis [1], we observed a significant number of prevailing MHC-II+ cells, a marker of activated microglia and myeloid derived immune cells, including peripheral blood macrophages and monocytes, in the brain of the Thy1-HEXB;HexB−/− mice. The gene discussed is HEXB; the disease is GM2 gangliosidosis.