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DIABETES

What is Diabetes?

When you or someone you love has diabetes, you discover that you must think about a part of life that others take for granted. Your never-changing goal becomes reaching a subtle balance between glucose and insulin. The more learn about diabetes, the better you can be at your balancing act, and the richer your life shared with this chronic disease can be.

TYPES OF DIABETES

Diabetes refers to a set of several different diseases. The most common types of diabetes are type 1, or immune-mediated diabetes mellitus, and type 2, or insulin - resistant diabetes mellitus. A third type of diabetes, gestational diabetes mellitus, occurs during some pregnancies.

All types of diabetes have similar symptoms, because all forms of the disease result in too much sugar, or glucose, in the blood. This is because your body is unable to remove glucose from your blood and deliver in to the cells in your body. Your cells use glucose as a source of energy in order to say alive. But the reasons why your body cannot use glucose from the blood are different for type 1 and type 2 diabetes.

People with type 1 diabetes do not make enough insulin. Insulin is a small protein made by the pancreas that helps the body use or store glucose from food. People with type 1 diabetes can be treated with injections of insulin. In contrast, people with type 2 diabetes, like women with gestational diabetes, do make insulin, but for some reason, the cells in their bodies are resistant to insulin's action or they don't make enough insulin. In all types of diabetes, if glucose does not get into the cells and tissues that need it, it accumulates in the blood.

About half of all cases of type 1 diabetes appear in childhood or in the early teenage years. For this reason, it used to be called juvenile-onset diabetes. If your symptoms first appeared during the early teenage years, your doctor probably suspected diabetes right away. If you were a young child when the disease developed, it might have occurred so fast that you went into a coma, before anyone suspected diabetes. Type 2 diabetes most often develops in adulthood and used to be called adult-onset diabetes. Usually, it does not appear suddenly. Instead, you may have no noticeable symptoms or only mild symptoms for years before diabetes is detected, perhaps during a routine exam or blood test. Gestational diabetes only appears during pregnancy in women with no previous history of type 1 or type 2 diabetes and goes away after pregnancy. Pregnant women are tested for gestational diabetes.

All people with diabetes have one thing in common. They have too much sugar, or glucose, in their blood. People with very high or poorly controlled blood glucose level share many similar symptoms.

• An unusual thirst
• A frequent desire to urinate
• Blurred vision
• A feeling of being tried most of the time for no apparent reason.

People with type 2 diabetes may also experience leg pain that may indicate nerve damage or poor circulation. Many people with type 1 diabetes and some people with type 2 diabetes also find that they lose weight even though are hungrier than usual and are eating more.

Even if they have lost weight, people with type 2 diabetes still tend to be overweight. Three-fourths of all people with type 2 diabetes are or have been obese - that is, they are at least 20 percent over their desirable body weight. Type 2 diabetes tends to develop in people who have extra body fat. Where you carry your excess fat may determine whether you get type 2 diabetes: Extra fat above the hips is riskier than fat in the hips and thighs for developing for 2 diabetes. And leading an inactive "couch potato" lifestyle can also leads to diabetes. It also contributes to obesity.

If you have recently been diagnosed with diabetes, you are not alone. Nearly 16 million Americans - about one of every 17 people - have the disease. About 1,800 new cases each year. Ninety to ninety-five percent of all cases of diabetes in people over age 20 are type 2 diabetes. And half of all people with type 2 diabetes are unaware they even have the disease. Because of the nature of type 2 diabetes, it is possible to have mild symptoms or signs of type 2 diabetes for years before diabetes worsens. In contrast, few cases of type 1 diabetes go undetected to long. The symptoms of type 1 diabetes are severe enough that the person goes to the doctor for help.

WHO HAS DIABETES?

Almost 16 million Americans have diabetes. This is about 6 percent of the people in the country. In 1999, it was estimated that 500,000 to 1 million people had type 1 diabetes. It is hard to get an exact count of the number of people with diabetes because we have no nationwide diabetes registry. Slightly under half of the people with type 1 diabetes are children and teenagers age 20 and younger. Type 1 diabetes is more common in whites than in African Americans, Hispanic Americans, Asian Americans, and Native Americans.

In 1999, it was estimated that about 9.5 million people had diagnosed type 2 diabetes. Another 5 to 6 million people are undiagnosed. It is common in older people. Nearly 11 percent of Americans age 65 to 74 have type 2 diabetes. It is more common in some ethnic groups than others. In American age 45 to 74, over 14 percent of Mexican Americans and Puerto Rican Americans have type 2 diabetes, over 10 percent of African Americans have type 2 diabetes, and about 6 percent of Cuban Americans and whites have type 2 diabetes. Type 2 diabetes is even more common in Nature Americans: In some groups, almost half of adults age 30 to 64 have type 2 diabetes.

About 135,000 women develop gestational diabetes each year. Of these, about 40 percent get type 2 diabetes within 15 years.

TESTS FOR DIABETES

Although your physician may suspect that you have diabetes because of your symptoms, the only sure way to tell is with blood tests. Blood tests are used to diagnose both type 1 and type 2 diabetes, as well as gestational diabetes. Your doctor may repeat your blood tests to be sure of the diagnosis.

The blood tests are based on the fact that diabetes keeps your blood glucose, or sugar, levels above normal some or all of the time. Your blood glucose levels may be high even though you haven't eaten recently. In addition, your body cannot get rid of the extra glucose that appears in the blood after eating.

Random plasma glucose tests are the simplest way to detect diabetes. This test measures the amount of glucose in the blood at any given time and is done without fasting. If you have obviously symptoms of diabetes and the amount of glucose in your blood is 200 mg/dl or higher, your doctor will diagnose diabetes. Symptoms of diabetes include frequent urination, intense thirst, blurred vision, unexplained weight loss, and extreme tiredness.

The preferred method for diagnosing diabetes is the fasting plasma glucose test. For this test, your doctor will ask you not to eat for at least 8 to 10 hours. Then, a sample of your blood is taken, and the amount of glucose present in the blood is measured. Normally after fasting, the amount of glucose is less than 126 mg/dl, the doctor will suspect diabetes. In diabetes, extra glucose remains in the blood, even after fasting, because it cannot enter the body's cells. This is due to a lack of insulin or resistance to the action of insulin. Doctors usually make a firm diagnosis of diabetes when two fasting plasma glucose tests, done on different days, are over 126 mg/dl.

If your test results are greater than 110 mg/dl but less than 126
mg/dl, you may be diagnosed with impaired fasting glucose. This is not diabetes, but sometimes occurs before diabetes, usually type 2 diabetes, develops. Some people with impaired glucose tolerance nerve get diabetes. However, some of the same problems that result from having diabetes also occur in people with impaired glucose tolerance. If you have been diagnosed with impaired glucose tolerance, your physician will want to watch carefully for diabetes. Also, you need to talk with your doctor about reducing your risk of heart disease, keeping your weight in the healthy range, and exercising regularly to lower your chances of developing diabetes.

Not Sure Which Type of Diabetes You Have?

Your characteristics	Do I have type 1 diabetes?	Do I have type 2 diabetes?
Age 10 at diagnosis	Probably	Not likely
Age 20 at diagnosis	Probably	Not likely
Age 30 at diagnosis	Probably	Not likely
Age 40 at diagnosis	May be	May be
Age 50 at diagnosis	Not likely	Probably
Age 60 at diagnosis	Not likely	Probably
Age 70 at diagnosis	Not likely	Probably
Under weight at diagnosis	Probably	Not likely
Normal weight at diagnosis	May be	May be
Overweight at diagnosis	Yes	May be
Large amount of ketones in urine from time to time	Yes	No
Family history of type 1 diabetes	Yes	May be
Family history of type 2 diabetes	May be	Yes
Previous gestational diabetes	No	Yes
Use insulin	Yes	Yes
Use oral diabetes medication	Only for the first few months, if at all	Yes
Use no diabetes medication	No	Yes

 

Certain pregnant women with no history of diabetes are at high risk for developing gestational diabetes. These are women who are 25 years of age or older, are overweight, have a patient or sibling with diabetes, or are Hispanic, Native American, Asian, or African-American.

If you have nay of these characteristics, your obstetrician will screen you for gestational diabetes with a glucose challenge. This is done between the 24th and 28th weeks of pregnancy. At this time, the hormones of pregnancy naturally begin to cause temporary insulin resistance that lasts until the baby is born. The glucose challenge helps your doctor determine whether your body is able to overcome the insulin resistance on its own. You are given a glucose drink to finish at a certain time, without regard to eating. If the glucose in your blood 1 hour later is 140 mg/dl or above, you may have gestational diabetes. Your doctor will need to give you another test, for which you may need to fast, for a firm diagnosis.

TYPE 1 OR TYPE 2?

If tests reveal that you have diabetes, your doctor must then decide whether you have type 1 or type 2 diabetes. Although the symptoms and blood test results are similar for both type 1 and type 2 diabetes, the cause are very different.

DIABETES : FACT OR MYTH?

"I used to have type 2 diabetes, but now I have type 1 diabetes. My doctor put me on insulin last year".

Lot of people, over 40 percent of adults with diabetes, use insulin. But because there are about 90 adults with type 2 diabetes to every 5 adults with type 1 diabetes, this means there are a lot of people with type 2 diabetes must use insulin to make up for their pancreas no longer making it. You don't necessarily have type 1 diabetes just because you have to take insulin. Many people with type 2 diabetes need extra insulin to overcome their body's resistance to the insulin already being made by the pancreas.

Type 1 diabetes and type 2 diabetes, while having a lot in common, are two different disease. They have different causes. The type of diabetes you have does not change as you age or if you lose or gain weight or change treatment.

It will help your doctor to know whether there has been type 1 or type 2 diabetes in your family. Your age is not the only clue about what type of diabetes you have. It's true that most people younger than age 20 who show signs of diabetes have type 1 diabetes and that most people diagnosed with diabetes when they're over age 30 have type 2 diabetes. But there are exceptions. In some cases, families carry a genetic trait for developing type 2 diabetes as young people. And in some Native American families, obesity is so prevalent that children as young as 10 years old have type 2 diabetes.

If you are overweight or obese, it is more likely that you have type 2 diabetes.

• If you suddenly developed signs of diabetes, such as frequent urination, unusual thirst and hunger, and weight loss, perhaps after an illness, and are a young adult or child, it is more likely that you have type 1 diabetes.
• If you are not overweight and there are ketones in your urine, it is more likely that you have type 1 diabetes.
• If you are African American or Hispanic American, are older than 50, are overweight, and haven't been feeling quite "right" for along time, it is more likely that you have type 2 diabetes.
• If your doctor treats you with insulin injections, you could have either type 1 or type 2 diabetes.

WHO GETS DIABETES?

The risk factors associated with type 1 or type 2 diabetes are different. For both type 1 and type 2 diabetes, having a family hisotry of diabetes puts you at a higher risk for developing the disease than for a person with no family hisotry of diabetes. However, many people with type 1 diabetes have no known family history of the disease. Type 1 diabetes is more common among whites than among members of other racial groups. In contrast, members of Native American, African American, and Hispanic ethnic groups are at higher risk for developing type 2 diabetes. Perhaps the genetic make up of nonwhites predisposes them to the obesity and diabetes that tend to result from a 20th century sedentary American lifestyle.

A major difference in the characteristics of individuals with type 1 and type 2 diabetes is the age of onset. Typically, type 1 diabetes develops in individuals under the age of 40. Half of all people diagnosed with type 1 diabetes are under the age of 20. In contrast, most of the

people diagnosed with type 2 diabetes are over the age of 30, although type 2 diabetes is on the rise in teenagers. The risk for type 2 increases with age. Half of all new cases of type 2 diabetes ae in people age 55 and older.

Type 2 diabetes is more common in overweight and obese individuals, whereas body weight does not seem to be a risk factor for type 1 diabetes. Type 2 diabetes is often found in women with a history of giving birth to babies weighing more than 9 pounds an din women who were previously diagnosed with gestational diabetes. In both men and women, high blood pressure and very high concentrations of fats in the blood are more common in people with type 2 diabetes.

You can't get diabetes - either type 1 or type 2 - from stress, exposure to someone who already has diabetes, or from something you ate. And although diabetes may reveal itself after an illness or a stressful experience, these may have only speeded up the appearance of the disease.

CAUSES OF TYPE 1 DIABETES

In people with type 1 diabetes, the immune system mistakenly destroys the insulin - producing beta cells in the pancreas, treating them as if they were a foreign invander. This is called an autoimmune response. Autoimmune responses also occur in other disease such as multiple sclerosis, lupus, and thyroid diseases like hypothyroidism and hyperthyroidism. Researchers do not know exactly why this happens. But for diabetes, researchers have found many factors that appear to be linked to type 1 diabetes. These include genetics, autoantibodies, viruses, cow's milk and oxygen free radicals.

GENETICS

Scientists have long suspected that heredity plays a role in diabetes, especially in type 1 diabetes. This is because type 1 diabetes seems to run in families - if your mother or father had diabetes for example, you are more likely to develop the disease that someone without a family history. Also, type 1 diabetes seems to be more common in certain racial groups. Whites, for example, are more likely to develop the disease than are people from other racial backgrounds. Type 1 diabetes occurs in less than 1 in 100,000 people in Shanghai, China, but occurs in greater than 35 in 100,000 people in Finland.

Everyone is born with a set of instructions that tells the cells in your body how to grow live, and function. These instructions lie in the particular chemical sequence of units known as bases that make up the DNA in every cell in your body. Each cell in your body contains 46 chromosomes, which are made up of DNA of protein. Each DNA strand is like a long string that contain millions of bases. Along the strand lie the genes, unique segments of DNA that tell you cells what kind of protein to make.

But just as books sometimes contain typographical errors, so too does the sequence of DNA. If there is a mistake, or mutation, in the DNA within a gene, then a faulty protein may be made that can't do its job. Scientists are trying to determine how to mistakes in specific genes cause diabetes. If mutated genes occur in germ cells - the eggs and sperm - then the DNA mutations can be passed on from generation to generation.

Researchers have identified several different genes that might make a person more likely to develop type 1 diabetes, However, they have not found one single gene that makes all people who inherit it develop the disease. Instead, it sems that there are several genes known as "diabetes susceptibility" genes.

One particular set of genes that may predispose a person to diabetes is responsible for the human leukocyte antigens, or HLAs. These genes code for certain proteins called antigens, which identify a person's own cells as "self". They tell the immune cells not to destroy the cells that are part of person's body. Scientists believe that some HLA antigens incorrectly identify the beta cells as non-self. Then the immune cells, which normally destroy froeign invading cells, destroy these cells. This called autoimmunity - an immune attack on a person's own cells. In type 1 diabetes, the insulin - producing cells of the pancreas are destroyed in an autoimmune attack, and the body can no longer make insulin. This destructive process occurs over many months.

Each person has many kinds of HLA genes, and thus there are many typesof HLAs. Each person inherits one of each kind of HLA gene from each parent. One type of HLA gene, known as HLA-DR, is most strongly linked to type 1 diabetes. There are many variations of HLA-DR, but 95 percent of people with type 1 diabetes have the DR3 form, the DR4 form, or both. This makes researchers suspect that having the DR3 and DR4 variants may make a person more likely to get type 1 diabetes. However, this is not the whole answer, because 45 percent of people without type 1 diabetes have the DR3 or DR4 variants. Also, variants of another HLA gene, known as HLA-DQ, may also play a role in type 1 diabetes.

Just because a person inherits a susceptible HLA variant doesn't mean that person witll develop diabetes. Most people with DR3 or DR4 variants remain helathy. But if there is a family hisotry of type 1 diabetes, then screening may help predict the risk of developing the disease. For example, borthers and sisters of a person with diabetes who have two of the same HLA-DR variants have a 15 percent chance of getting type 1 diabetes. But if they share only one variant, the risk is only 5 percent. If no variants are the same, the risk of developing type 1 diabetes is 1 percent or less.

The more we study how people get type 1 diabetes, the more we understand that the answers are not simple. No one event or characteristic seems to bring on diabetes. Researchers have identified several other gene clusters on different chromosomes in addition ot these HLA variants that may also play a role in type 1 diabetes.

AUTOANTIBODIES

The immune system protects you from disease by killing germs and other foreign invaders. It does this largely through the action of white blood cells, or lymphocytes. T lymphocytes, or T cells, can attack foreign cells directly. B lymphocytes, or B cells, produce special proteins called antibodies that recognize this shapes of molecuels on the surface of specific invaders.

B cells sometimes manufacture antibodies that recognize a person's own cells. These self recognizing antibodies are called autoantibodies. Autoantibodies are found in many people with autoimmune disorders, but three autoantibodies are especially common in people with type 1 diabetes. These antibodies recognize :

• Islet cells (beta cells are just one type of islet cell in the pancreas)
• Insulin
• Glutamic acid decarboxylase, a protein made by the beta cells in the pancreas. This protein is also called GAD, or the 64K protein.

These three types of autoantibodies all seem to act as markers. Researchers believe that these antibodies contribute to the demise of the beta cells of the pancreas by identifying which cells are to be attached. It is really the T cells that ultimately destroy the insulin - producing cells of the pancreas. Of people newly diagnosed with type 1 diabetes, 70 to 80 percent have antibodies to islet cells, 30 to 50 percent have anitbodies to insulin, and 80 to 95 percent have antibodies to GAD.

The antibodies may be present several years before diabetes is dagnosed. The islet cell antibodies disappear later on. Because these antibodies are so common in people with type 1 diabetes and because they so often appear before the symptoms of diabetes appear, researchers are finding that theya re useful in screening people for type 1 diabetes who are at high risk for the disease. Although the risk for developing diabetes may only be 1 to 10 percent for people with a parent or sibling with the disease, a much higher percentage of people who also have antibodies to islet cells develop type 1 diabetes within 5 years. And for many, having combinations of these antibodies and certain HLA genes results in an even higher risk.

By testing relatives of people with type 1 diabetes for autoantibodies, doctors and researcheres can often predict who is likely to develop the disease. This could be especially useful as new therapies emerge, because they can be strated before damage to the pancreas is too extensive. For example, by identifying people who are likely to develop type 1 diabetes at are early stage, researchers may be able to treat with insulin or drugs that suppress the immune system and thus prevent the T cells from destroying the beta cells in the pancreas.

Some people with a high risk of getting type 1 diabetes have participated in studies to see whether immunosuppressants such as azathioprine or cyclosporine delay or prevent the onset of the disease. Researchers are also testing to see whether long-acting insulin, oral insulin, or nicotinamide can delay or prevent diabetes. These studies suggest that axathioprine or cyclosporine can reduce the dose of insulin needed in people who have already developed type 1 diabetes, if the drug is started at the time the disease is diagnosed.

Other therapies may also be tested as researchers learn more about how autoantibodies contribute to diabetes. For example, if autoimmunity to GAD turns out to be a primayr trigger of type 1 diabetes, it might be possible to develop a vaccine that would protect people from developing the disease.

VIRUSES

Perhaps surprisingly, many scientists also suspect that viruses may cause type 1 diabetes. This is because people who develop type 1 diabetes have often recently had a viral infection, and "epidemics" of type 1 diabetes often occur after viral epidemics. Viruses, like those that cause mumps and German measles and Coxsackie family of viruses, which is related to the virus that causes polio, may play some role in cauisng type 1 diabetes.

A small region of the GAD molecule is almost identical to a region of a protein found in the virus known as Coxsackie B4. The two similar protein regions probably have similar shapes and may be recognized by the same T cells. Thus, to a T cell hunting for foreign invaders, the GAD protein, which is part of the body, might look the same as the Coxsackie virus protein, which is part of an invading cell. After a viral infection by the Coxsackie virus, the T cell, bent on destroying the invading virus, might actually destroy the body's own beta cells that bear the GAD protein. This would destroy the cells that produce insulin and result in type 1 diabetes.

Other theories may also explain how a viral infection might lead to diabetes. Some researchers believe that when a virus in fects a body, it might somehow change the structure of the antigens on the surface of the islet cells. If this occurs, then the altered antigen might appear to be foreign to the immune system, and a person's own insulin-producing islet cells might be destroyed.

Gian Franco Bottazzo, a well-known diabetes researcher, has another theory. He believes that diabetes is a relatively new disease caused by a slow acting virus. Although such a virus has not been found, Bottazzo holds that the virus causes the immune system to attack proteins in the pancreas. A drastic increase in the number of cases of type 1 diabetes occurred on the island of Sardinia, Italy, in the 1960s and in Finland in the 1970s, and he believes that such a slow-acting virus could be the culprit.

COW'S MILK

It seems unlikely, but different kinds of food may pay a role in the development of type 1 diabetes. For example, one group of researchers found a connection between being fed cow's milk early in life and type 1 diabetes. They showed that children newly diagnosed with type 1 diabetes have higher amounts of antibodies that recognize a specific protein in cow's milk. These autoantibodies appear to bind to a protein that sometimes appears on the surface of the insulin-producing beta cells int eh pancreas after an illness. The researchers speculate that, after an illness, the transient protein may appear on the surface of beta cells. The immune response to the milk protein might be to then recognize the beta cell surface proteins and attack the beta cells, leading to a destruction of the insulin - producing cells of the pancreas, and thus, to type 1 diabetes.

However, other researchers have looked for but not found an increased risk of type 1 diabetes if cow's milk is given early in life and if breast feeding is done for a short period. Cow's milk is only one kind of food that may play a role in the development of type 1 diabetes. Studies in diabetes - prone rats show that withholding wheat and soy helps delay or prevent diabetes.

OXYGEN FREE RADICALS

No, these are not part of some terrorist organization, but they may as well be. Oxygen free radicals, formed a s a by product of many chemical reactions in the body, wreak havoc wherever they go. Normally, the body has ways of quenching free radicals. But smoke, air pollution, diet, and even genetics can be contribute to the formation of excessive amounts of free radicals, which the body cannot always handle. Uncontrolled, the reactive molecules can destroy the body's own cells as well as bacteria. Oxygen free radicals contribute significantly to the aging process and to the development of several other diseases. Researchers have implicated free radicals in the development of amyotrophic lateral sclerosis (ALS), or Lou Gehrig's disease, a degenerative neuromuscular disease.

Some researchers believe that oxygen free radicals may also contribute to type 1 diabetes. Islet cells have very low levels of the enzymes that break down free radicals. Thus, agents that increase free radical production could result in destruction of pancreatic cells. If this is true, then researchers may be able to develop drugs that block the formation of free radicals in the islet cells.

CHEMICALS AND DRUGS

Several chemicals have been shown to trigger diabetes. Pyriminil, a poison used to kill rats, can trigger type 1 diabetes. Two prescription drugs, pentamidine, used to treat pneumonia, and L-asparaginase, an anticancer drug, can also cause type 1 diabetes. Other chemicals have been shown to make animals diabetic, but scientists don't know for sure whether they have the same effect in humans.

It is unlikely that either genetics or environmental factors alone cause diabetes. But it does appear that a person could start with a genetic susceptibility - the inheritance of a particular set of genes. If this person is then exposed to some environmental "triggering" factor, such as a virus or a chemical, then diabetes may develop. Although no one is destined to develop diabetes with certainty, a person's heredity increases the odds.

CAUSES OF TYPE 2 DIABETES

The reasons that type 2 diabetes occur are different from those that trigger type 1 diabetes. Unlike people with type 1 diabetes, who become unable to produce insulin, people with type 2 diabetes produce insulin. But, either the body does not respond to insulin's action - it's resistant - or there is just not enough insulin to go around - there's too much body for the amount of insulin that's made. Either problem leads to the same outcome: insulin can't deliver glucose to the cells that need it, and there's too much glucose in the blood.

Virtually all cells in the body contain special proteins called receptors that bind to insulin. They work like a lock and key. In order for glucose to enter the cell, insulin must first fit into the insulin receptor. But for some reason, in some people with type 2 diabetes, there is a faulty lock, or insulin receptor. The key doesn't open the lock, and glucose is shut out of the cell. And in some people with type 2 diabetes, there are not enough locks, or insulin receptors, on the cells to allow enough glucose to enter. But for most people with diabetes it's not so much that the key doesn't fit the lock, but that insulin doesn't work properly. In rare cases, the insulin is mutated, or built incorrectly, and does not fit the insulin receptor.

In addition to problems with insulin and the insulin receptor, in many people with type 2 diabetes, the beta cells in the pancreas do not produce enough insulin. Without enough insulin to meet the body's needs glucose level rise and diabetes results. Scientists do not know why the pancreas does not function well in these people. Some believe that the system that controls glucose levels in the blood and tells the pancreas to make more insulin does not function properly. Other think that the pancreas, after many years of working overtime, overproducing insulin to overcome insulin resistance, simply begins to "burn out."

Although researchers do not fully understand why type 2 diabetes develops, they have uncovered many factors that may contribute to the disease.

GENETICS

Genetics also appear to play a role in how type 2 diabetes develops. Like type 1 diabetes, type 2 diabetes also appears to run in families, and it is most likely due to the inheritance of certain genes. The link to genetics seems even stronger in type 2 diabetes than in type 1 diabetes. If a person with type 1 diabetes had an identical twin, there is a 25 to 50 percent chance that the twin, will develop diabetes. But if a person with type 2 diabetes has an identical twin, there is 60 to 75 percent chance that the person will develop diabetes.

More evidence for the role of genes in type 2 diabetes comes from studying minorities. Compared with whites, African Americans, Asian Americans, Hispanic Americans, and Native Americans all get type 2 diabetes more often. Native Americans have the highest rate of type 2 diabetes in the World. Hispanic groups, such as Mexican Americans, that share genes with Native American groups have a higher rate of type 2 diabetes than Hispanic groups, such as Cuban Americans, where less intercultural contact has occurred.

Researchers have not yet isolated a single "type 2 diabetes" gene, but they are finding errors in several that may contribute to type 2 diabetes. For example, researchers have identified a protein called PC-1 that shuts down the insulin receptor, which creates insulin resistance. This protein is prevalent in most people with type 2 diabetes, compared with people without diabetes. For some reason, too much of the inhibitor protein is made in some people, and the insulin receptor cannot do its job properly, which can lead to insulin resistance.

Researchers believe that the genes that lead to obesity may also play a role in diabetes. In mice, scientists have identified a gene they called the obese gene. The obese gene appears to regulated body weight by making proteins that affect the center in the brain that tells you whether you're full or hungry. When the obese gene is mutated, the mice become obese and develop type 2 diabetes.

AGE, OBESITY, AND LIFESTYLE

The most important environmental trigger of type 2 diabetes appears to be obesity. Obesity is defined as weighing more than 20 percent over your desirable body weight. Genetics may play a role in obesity and, thus, in triggering type 2 diabetes.

In some way, having too much body fat promotes resistance to insulin. This is why, for so many years, type 2 diabetes has been treated with diet and exercise. Losing weight and increasing the amount of muscle while decreasing the amount of fat helps the body use insulin better. There is also a link between type 2 diabetes and where your body is too fat. People with central body obesity, which means carrying excess fat above the lips, have a higher risk of developing type 2 diabetes than those with excess fat on the hips and thighs.

Central body obesity, as well as overall obesity, is more common in African Americans than in whites. This may be one reason why type 2 diabetes is also more common in African Americans than in whites.

Age also appears to play a role. Half of all new cases of type 2 diabetes occur in people over age 55. Because people tend to gain weight as they age, many researchers think that the reason more older people develop diabetes is because more older people are overweight.

Leading an inactive, sedentary lifestyle and consuming a high-calorie diet can also lead to type 2 diabetes, presumably by contributing to obesity. Obesity, as well as type 2 diabetes, are common in Asian Americans and Hispanic Americans who have "westernized" their eating and activity habits.

CAUSES OF GESTATIONAL DIABETES

Like the other types of diabetes, the exact cause of gestational diabetes is unknown. However, experts do have some clues.

HORMONES

During pregnancy, the placenta, which is the organ that nourishes the growing baby, produces large amounts of various hormones. Hormones are important for the baby's growth. However, these hormones may also block insulin's action in the mother's body, causing insulin resistance. All pregnant women have some degree of insulin resistance.

Gestational diabetes usually appears around the 24th week of pregnancy. This is when the placenta begins producing large quantities of the hormones that cause insulin resistance. For this reason, the period between the 24th and 28th weeks of pregnancy is a good time to screen for gestational diabetes.

GENETICS

Because insulin resistance, rather than underproduction of insulin, seems to cause gestational diabetes it is more like type 2 diabetes than type 1 diabetes. And having gestational diabetes increases your chances of someday developing type 2 diabetes. Researchers suspect that the genes responsible for type 2 diabetes and for gestational diabetes may be similar.

Some women show signs of high blood glucose even before the 28th week of pregnancy. Doctors believe that these women probably had diabetes that was unrecognized before the pregnancy began. The weight gain and hormonal changes of pregnancy stressed the body and revealed the diabetes. This can happen with either type 1 or type 2 diabetes. Doctors would carefully watch what happens after the pregnancy in order to diagnose type 1 or type 2 diabetes.

OBESITY

Gestation diabetes is more common in groups that have more obesity. For instance, it is found more often in areas with a large number of Hispanic Americans, in whom obesity is more common. Obesity can trigger gestational diabetes as well as type 2 diabetes.