The level of plasma XOR activity was significantly associated with diabetes mellitus, dyslipidemia, and hyperuricemia as well as with body mass index, waist circumference, insulin resistance, eGFR, and the plasma level of hepatic enzymes, triglycerides, fasting glucose, insulin, and glycated hemoglobin in the Tanno–Sobetsu Study involving 627 Japanese subjects (292 men, 335 women) aged 65 ± 15 years [67]. This evidence concerns the gene XDH and metabolic syndrome.