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disorder usually develops before age 30, often during childhood. Type 1 diabetes is caused by a combination of genetic predisposition and environmental factors, possibly including infection by a virus. More than 90% of diabetics have type 2 diabetes. This disorder develops gradually, usually in overweight people. In type 2 diabetes, normal (or greater than normal) concentrations of insulin are present in the blood, but insulin receptors on target cells do not bind it, a condition known as insulin resistance. Biologists do not fully understand the causes of insulin resistance, but do know there is a strong genetic component. Even if identical twins are raised separately in very different environments, when one identical twin develops insulin resistance the other twin almost always doe also. Investigators have also reported an association between increased fat tissue and insulin resistance. Many type 2 diabetics can keep their blood glucose levels within normal range by diet management, weight loss, and regular exercise. When this treatment approach is not effective, they are treated with oral drugs that stimulate insulin secretion and promote its actions. Approximately one third of type 2 diabetics eventually need insulin injections." (*Brooks/Cole-Thomson Learning Biology 7th Edition)
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