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Definition
Diabetes mellitus describes a group of diseases in which there is an elevated level of the sugar glucose, the body's main source of energy for cellular functions, in the blood. The level of glucose, as well as other "fuel" molecules, is increased due to a disorder in the production or function of the hormone insulin. A range of health problems occurs primarily due to the damaging effects of elevated levels of glucose on blood vessels.
Description
To understand diabetes, it is important to understand how the hormone insulin functions in the breakdown and utilization of glucose. Insulin acts in two ways. It is necessary for the transport of glucose and other fuel molecules into the cells. It also regulates several pathways in metabolism that are important in the utilization of these fuel molecules. Insulin is made and released by specialized cells of the organ known as the pancreas. These beta cells of the pancreas release insulin when blood levels of glucose, amino acids, fatty acids, and ketones are high. These are all breakdown products of food, and an increase in their level in the blood signals that a person has recently eaten. The insulin acts to mobilize each of these fuel molecules so they can be used as energy to support cellular functions needed to maintain the body.
There are two main types of diabetes mellitus: type I and type II diabetes. While there are similarities, type I and type II diabetes differ in several aspects related to cause, symptoms, treatment, and associated risk factors. In addition, there are other less common forms of diabetes.
Type I diabetes
Also called insulin-dependent diabetes mellitus (IDDM), this is the most severe form of diabetes, in which shots of insulin are necessary on a daily basis. IDDM is thought to be an autoimmune condition in which one's own immune system attacks and destroys the insulin-producing cells of the pancreas. Insulin production is low or absent, and onset is generally in childhood or early adulthood. Affected individuals tend to be thin and prone to events in which ketones can become so high in the blood as to be potentially life-threatening, a complication called ketosis.
Type II diabetes
The most common type of diabetes, non-insulin dependent diabetes mellitus (NIDDM or type II), is the milder form of diabetes. Symptoms can generally be controlled with diet or oral medications that decrease blood sugar levels. True NIDDM does not develop into the insulin-dependent type of diabetes. In NIDDM, blood sugar levels become elevated because of resistance to the effects of insulin, which is usually present at normal levels. In other words, there may be plenty of insulin available, but the cells are not sensitive to insulin's effects. This results in the inability of insulin to move glucose to the inside of cells where it can be used. NIDDM typically develops after age 40, although it can occur at any age. Affected individuals tend to be obese and are not prone to ketosis.
Impaired glucose tolerance (IGT)
Impaired glucose tolerance is a symptom characterized by lab test results that indicate elevated blood glucose levels. The results are not abnormal enough to be called "diabetes." However, IGT may be an early sign of NIDDM, and is certainly a risk factor for developing NIDDM.
MODY
Clinical severity is determined in part by the specific gene associated with disease within a family. MODY3 mutations result in the most severe clinical presentation, with 97% of cases having NIDDM, as opposed to impaired glucose tolerance. Individuals with MODY1 commonly experience vascular complications and require insulin in one-third of cases. Glucokinase (GCK) gene mutations, although the most common cause of MODY, tend to result in the mildest clinical picture. Approximately 46% have NIDDM, and the remaining individuals have IGT. Individuals with GCK-related MODY rarely need insulin and usually don't experience vascular complications.
Gestational diabetes
Also called diabetes of pregnancy, this form of the disease is often limited to the time during which a woman is pregnant. Management of glucose levels in affected women during pregnancy is very important, because high glucose levels can have serious, negative effects on the developing fetus. Gestational diabetes usually disappears after delivery. However, history of gestational diabetes increases a woman's risk of developing NIDDM in the future and of having gestational diabetes again in future pregnancies. Risk factors for gestational diabetes are similar to those for NIDDM.
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Author Info: Jennifer Denise Bojanowski MS, CGC, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Genetic Disorders Part I, 2002 |
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