Patients with HT and/or CD shared a common genetic susceptibility regarding genes encoding the major histocompatibility complex (HLA-B8, HLA-D3, HLA-DQ2, and HLA-DQ8), the cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), IL-18, and IFN-γ (14). This evidence concerns the gene CTLA4 and hematocrit.