Logistic regression to simultaneously estimate the odds ratios of FGF19 and FGF21 for diabetes (i.e. to determine if they were acting independently and/or test for a synergistic effect), showed that both FGF19 < 200 (OR = 3.73, 95% CI = [1.08, 12.84], p = 0.037) and FGF21 > 500 (OR = 4.28, 95% CI = [1.20, 15.27], p = 0.025) were independently associated with diabetes, but the interaction (i.e. synergistic effect) was not significant (p = 0.594). The gene discussed is FGF19; the disease is diabetes mellitus.