HLA-B and Huntington disease: Additionally, in the higher scored network (n = 50, p < 0.0001) built by IPA using the top selected down-regulated genes in HD patients were included class I human leukocyte antigen genes (HLA-A, HLA-B, HLA-C, HLA-E, HLA-F, HLA-G) and those encoding activation cell surface molecules such as CD40L and FASL (Figure 2B).