Alterations in the expression of the CAT gene and the CAT protein level have been reported in a wide variety of diseases, and polymorphisms in the CAT gene have been shown to be associated with various pathophysiological conditions, such as IR, T2DM, type 1 diabetes mellitus (T1DM), gestational diabetes, impaired glucose tolerance, HA, Alzheimer’s disease, breast cancer and therapy, asthma, osteonecrosis, elderly re-nutrition, and bone mineral density [19,20,21,22,23,24,25,26,27,28]. The gene discussed is CAT; the disease is diabetes mellitus.