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You've probably
wondered how you got diabetes. You may worry that your children
will get it too. Unlike some
traits, diabetes does not seem to be inherited in a simple
pattern. Yet clearly, some people are born more likely to get
diabetes than others.
What
leads to diabetes?
Type 1 and type 2
diabetes have different causes, yet two factors are important in
both:
Conclusion: Genes
alone are not enough - One proof of this is identical twins:
Identical twins have identical genes, yet when one twin has type
1 diabetes, the other gets the disease at most only half the
time. When one twin has type 2 diabetes, the other's risk is at
most 3 in 4.
Type
1 diabetes
In most cases of
type 1 diabetes, people need to inherit risk factors from both
parents. We think these factors must be more common in whites
because whites have the highest rate of type 1 diabetes. Because
most people who are at risk do not get diabetes, researchers
want to find out what the environmental triggers are.
One trigger might
be related to cold weather. Type 1 diabetes develops more often
in winter than summer and is more common in places with cold
climates. Another trigger might be viruses. Perhaps a virus that
has only mild effects on most people triggers type 1 diabetes in
others.
Early diet may
also play a role. Type 1 diabetes is less common in people who
were breastfed and in those who first ate solid foods at later
ages.
In many people,
the development of type 1 diabetes seems to take many years. In
experiments that followed relatives of people with type 1
diabetes, researchers found that most of those who later got
diabetes had certain auto-antibodies in their blood for years
before.
[Antibodies are
proteins that destroy bacteria or viruses. Auto-antibodies are
antibodies 'gone bad,' which attack the body's own tissues].
Type
2 diabetes
Type 2 diabetes
has a stronger genetic basis than type 1, yet it also depends
more on environmental factors. Sound confusing? What happens is
that a family history of type 2 diabetes is one of the strongest
risk factors for getting the disease but it only seems to matter
in people living a Western lifestyle.
Americans and
Europeans eat too much fat and too little carbohydrate and
fiber, and they get too little exercise. Type 2 diabetes is
common in people with these habits. The ethnic groups in the
United States with the highest risk are African Americans,
Mexican Americans, and Pima Indians.
In contrast,
people who live in areas that have not become Westernized tend
not to get type 2 diabetes, no matter how high their genetic
risk.
Obesity is a
strong risk factor for type 2 diabetes. Obesity is most risky
for young people and for people who have been obese for a long
time.
Gestational
diabetes
Gestational
diabetes is more of a puzzle. Women who get diabetes while they
are pregnant are more likely to have a family history of
diabetes, especially on their mothers' side. But as in other
forms of diabetes, non-genetic factors play a role. Older
mothers and overweight women are more likely to get gestational
diabetes.
Type
1 diabetes: your child's risk
In general, if
you are a man with type 1 diabetes, the odds of your child
getting diabetes are 1 in 17. If you are a woman with type 1
diabetes and your child was born before you were 25, your
child's risk is 1 in 25; if your child was born after you turned
25, your child's risk is 1 in 100.
Your child's risk
is doubled if you developed diabetes before age 11. If both you
and your partner have type 1 diabetes, the risk is between 1 in
10 and 1 in 4.
There is an
exception to these numbers. About 1 in every 7 people with type
1 diabetes has a condition called type
2 polyglandular autoimmune syndrome.
In addition to
having diabetes, these people also have thyroid disease and a
poorly working adrenal gland. Some also have other immune system
disorders. If you have this syndrome, your child's risk of
getting the syndrome including type 1 diabetes is 1 in 2.
Researchers are
learning how to predict a person's odds of getting diabetes. For
example, most whites with type 1 diabetes have genes called
HLA-DR3 or HLA-DR4.
If you and your
child are white and share these genes, your child's risk is
higher. (Suspect genes in other ethnic groups are less well
studied. The HLA-DR7 gene may put African Americans at risk, and
the HLA-DR9 gene may put Japanese at risk.)
Other tests can
also make your child's risk clearer. A special test that tells
how the body responds to glucose can tell which school-aged
children are most at risk.
Another more
expensive test can be done for children who have siblings with
type 1 diabetes. This test measures antibodies to insulin, to
islet cells in the pancreas, or to an enzyme called glutamic
acid decarboxylase. High levels can indicate that a child has a
higher risk of developing type 1 diabetes.
Type
2 diabetes: your child's risk
Type 2 diabetes
runs in families. In part, this tendency is due to children
learning bad habits eating a poor diet, not exercising--from
their parents. But there is also a genetic basis.
In general, if
you have type 2 diabetes, the risk of your child getting
diabetes is 1 in 7 if you were diagnosed before age 50 and 1 in
13 if you were diagnosed after age 50.
Some scientists
believe that a child's risk is greater when the parent with type
2 diabetes is the mother. If both you and your partner have type
2 diabetes, your child's risk is about 1 in 2.
People with
certain rare types of type 2 diabetes have different risks. If
you have the rare form called maturity-onset diabetes of the
young (MODY), your child has almost a 1-in-2 chance of getting
it, too.
More
Information on Genetics
If you would like
to learn more about the genetics of all forms of diabetes, the
National Institutes of Health has recently published The
Genetic Landscape of Diabetes. This free online book
provides an overview of the current knowledge about the genetics
of type 1 and type 2 diabetes, as well other less common forms
of diabetes. The book is written for health professionals and
for people with diabetes interested in learning more about the
disease.
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