When lowest ABI was used as a dependent variable, plasma total CatS (P = 0.002), active CatS (P = 0.001), and cystatin C (P = 0.046) associated significantly and negatively with lowest ABI after adjustments for familial AAA; smoking; coexisting diabetes mellitus; hypertension; use of ACE inhibitors, β–blockers, or statins; systolic and diastolic blood pressures; BMI; and aortic diameter. The gene discussed is ACE; the disease is diabetes mellitus.