Diabetes

Type 1 diabetes mellitus can occur at any age and is characterized by the marked inability of the pancreas to secrete insulin because of autoimmune destruction of the beta cells. It commonly occurs in children, with a fairly abrupt onset; however, newer antibody tests have allowed for the identification of more people with the new-onset adult form of type 1 diabetes mellitus called latent autoimmune diabetes of the adult (LADA). The distinguishing characteristic of a patient with type 1 diabetes is that, if his or her insulin is withdrawn, ketosis and eventually ketoacidosis develop. Therefore, these patients are dependent on exogenous insulin.

Type 2 diabetes mellitus was once called adult-onset diabetes. Now, because the epidemic of obesity and inactivity in children, type 2 diabetes is occurring at younger and younger ages. Although type 2 diabetes typically affects individuals older than 40 years, it has been diagnosed in children as young as 2 years of age who have a family history of diabetes.

Type 2 diabetes is characterized by peripheral insulin resistance with an insulin-secretory defect that varies in severity. For type 2 diabetes to develop, both defects must exist: All overweight individuals have insulin resistance, but only those with an inability to increase beta-cell production of insulin develop diabetes. In the progression from normal glucose tolerance to abnormal glucose tolerance, postprandial glucose levels first increase. Eventually, in hepatic gluconeogenesis increases, resulting in fasting hyperglycemia.

About 90% of patients who develop type 2 diabetes are obese. Because patients with type 2 diabetes retain the ability to secrete some endogenous insulin, those who are taking insulin do not develop DKA if they stop taking it for some reason. Therefore, they are considered to require insulin but not to depend on insulin. Moreover, patients with type 2 diabetes often do not need treatment with oral antidiabetic medication or insulin if they lose weight.

Maturity-onset diabetes of the young (MODY) is a form of type 2 diabetes that affects many generations in the same family with an onset in individuals younger than 25 years. Several types exist. Some of the genes responsible can be detected by using commercially available assays.

A variety of other types of diabetes, previously called secondary diabetes, are caused by other illnesses or medications. Depending