RET and medullary thyroid gland carcinoma: The allelic frequency of RET G691S polymorphism was 19.6% in the control subjects and 23.5% among MTC cases, and patients with RET G691S polymorphisms exhibited an increased risk of MTC compared to controls (OR = 1.22, 95%CI [1.06–1.39], p = 0.0049) [112].