Type 1 diabetes is due to an autoimmune destruction of the insulin-producing cells in the pancreas. Type 1 diabetes usually appears in people who have one or more genes that make them susceptible to the disease, with or without a family history of type 1 diabetes.
Type 2 diabetes is much more common and has several predisposing factors such as genetic causes (family history, increased risk in certain ethnic groups) and environmental conditions (unhealthy diet, obesity, lack of physical activity).