Foot gangrene is one of the most dreaded forms of diabetic foot. It may initially present as frequent cramping of the legs with long distance walks. It is worsened with smoking, uncontrolled hypertension and high blood cholesterol levels. The risk of foot amputation is around 15x higher for diabetics (Gayle R, Benjamin AL, Gary NG. The burden of diabetic foot ulcers. The American Journal of Surgery 1998Aug 24; 176(Suppl 2A):65-105).
Diabetes complications like this are preventable with early diagnosis and good control of blood sugars (http://www.nejm.org/doi/full/10.1056/NEJMe0807625).