In particular, the proportion of the population which has comorbidities such as diabetes mellitus (a known risk factor for HZ), and immunocompromising conditions such as solid organ transplants, cancer, leukemia/lymphoma, or being on medications that decrease T-cells (TNF-alpha inhibitors, DMARDS, corticosteroids) has increased over time, leading to increased numbers of patients being at risk for HZ/PHN [59]. This evidence concerns the gene TNF and diabetes mellitus.