Diabetes mellitus

Diabetes is a metabolic disease caused by the body's inability to use the hormone insulin to effectively convert carbohydrates into the simple sugar glucose that cells store and use to perform vital functions. Without glucose to fuel their activity, the cells use fat instead, producing ketones as a waste product. Ketones build up in blood and disrupt brain functions. Common signs ofdiabetes are excessive thirst, urination, and fatigue. The disease can alsocause vision loss, decreased blood supply to hands and feet, pain, and skin infections. If left untreated diabetes can induce coma and cause death.

There are two main types of diabetes. Juvenile diabetes (also called Type I) occurs when the pancreas, a gland attached to the small intestine, fails to produce enough insulin; as a result, it is also referred to as insulindependent diabetes mellitus (IDDM). Maturity-onsetdiabetes, or Type IInon-insulin dependent diabetes mellitus (NIDDM), occurs when the body produces insulin but cannot use it efficiently. Juvenile diabetes is usually controlled by doses of insulin and a strict diet. Maturity-onset diabetes, which isoften accompanied by obesity, is usually controlled by diet alone.

Diabetes often runs in families. In the United States about ten percent of the caucasian population suffers from diabetes, and it is even more common among African-American, Mexican-American, and certain Native American groups.

The symptoms of diabetes were identified 3,500 years ago in Egypt and were also known in ancient India, China, Japan, and Rome. The Persian physician Avicenna (980-1037) described the disease and its consequences. Thomas Willis (1621-1675), an English epidemiologist, was the first modern western physician to discover that the urine of diabetics tasted sweet. In 1815, the French chemist Michel Eugène Chevreul discovered that the sweetness came from "grape sugar" or glucose. The disease's formal name diabetes, meaning a siphon or running through, and mellitus, relating to sweetness or honey, was first used in 1860.

Injury to the pancreas was linked to diabetic symptoms by several scientistsfrom the seventeenth to the nineteenth centuries. The existence of a pancreashormone to reduce the blood glucose level was first proposed in 1916 by theEnglish physiologist Edward Sharpey-Schäfer. Insulin was isolated in 1921 by the Canadians Frederick Banting and Charles Best (1899-1978), andin 1922 they used it for the first time to successfully treat fourteen-year-old Leonard Thompson of Toronto.

Diabetes is an autosomal dominant disease, but its expression is also thoughtto be influenced by other conditions, such as aging. Research on Type I diabetes shows that dominant genes either protect against the disease or increasesusceptibility to it. Advances in molecular genetics have led to large-scalestudies to identify the genes responsible for diabetes. The American Diabetes Association has established a national database that contains information and genetic material from families with Type II diabetes that will help investigators conduct genetic linkage studies to locate the specific genes involved. Scientists have already established that a gene on chromosome 7 is linked to Type II diabetes. When mutated, the gene produces a faulty enzyme that is unable to stimulate the pancreas to produce insulin.

Scientists are developing tests to accurately predict whether someone will develop diabetes or not by observing whether the immune system attacks the pancreas cells that make insulin. The research may also lead to a vaccine againstdiabetes and drugs to keep the immune system from identifying the pancreas as an enemy, similar to drugs that keep the body from rejecting transplanted organs. New therapies for diabetes are continually under development. For example, studies of a combination drug therapy using metformin and troglitazone has been shown to significantly lower blood glucose levels in Type II diabetespatients by reducing glucose secretion by the liver (metformin) and enhancing the body's use of insulin (troglitazone). Another area under investigationis the use of islet cell transplantation, a promising approach for replacingwhole organ transplantation by extracting and replacing only those cellular components that are needed to restore normal function. Islet cell transplantation could be a key to the successful replacement of the insulin-producing islets of Langerhans.

The seventh leading cause of death in the United States, diabetes remains a major health problem. Approximately 10.3 million people in the United States were diagnosed with diabetes in 1997, representing a six-fold increase over four decades. By the early 1990s, the costs associated with treating and caringfor diabetes patients was estimated at over $90 billion a year.

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