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[IP] RE: genetics of DM

Shevy wrote:
>I was wondering about the genetics of IDDM. Does
>anyone know what the genetic factor would be if
>diabetics would marry? Would that increase the risk
>for having a diabetic offspring? What about a single
>diabetic parent? Are there other genetic factors
>involved in a 2 diabetic-parent family such as
>increased risk for other inherited diseases due to the
>fact that parental genotypes have these similarities??
>I would like to read up on the subject but I can't
>really find anything.

The simple answer to your question is that the 
issue of genetics and disease is very complicated.
Here's a more complicated non-answer:

Most of the time, when a disease appears to have 
a genetic component, there's no single genetic factor 
that causes the disease in all the people who have the 
disease. The exception is single-gene disorders like 
sickle cell anemia and Huntington's disease. These 
single-gene disorders aren't all that common or rep-
resentative, but because we understand pretty well 
what causes them, journalists and others who are 
trying to explain genetic diseases to the public tend 
to use them as examples.

To explain more concretely what I mean: there's
a known "breast cancer gene." A woman who has
this gene (which I think is commonly found in
people of Eastern European Jewish descent) has
a high risk of developing breast cancer. But MOST
women who develop breast cancer don't have this
gene. They got breast cancer for some other reason
that we don't understand (yet). (In fact, I think that
there may now be several known breast cancer 
genes that tend to occur in different populations, 
but I'm not sure.)

The same is true for diabetes. Type 1 diabetes seems 
to run in some families. In those families, there is 
probably a genetic factor that's being passed on. In 
addition, some kind of environmental trigger is needed 
to cause the person to get diabetes, even if the gene is 
present. But not everyone who has type 1 diabetes has 
that same genetic factor. Type 2 diabetes seems even 
more strongly to run in families than type 1. It's even
more complicated, though, because type 2 comes in 
many sub-varieties and often seems to be caused by a 
cluster of problems that combine to create the disorder.
And the environmental causes (including behavior) are
even more complex. So once again, it's almost certainly 
not a single gene or combination of genes that cause the 
problem in every person who has the disease.

In other words, diabetes has an unknown number of
possible genetic causes and an unknown number of 
possible environmental causes. Statistically, it might 
be true that two people with diabetes would have a 
higher risk than a non-diabetic couple, or than a 
diabetic and non-diabetic, of having a child with a 
genetic predisposition toward developing diabetes. 
But figuring out what the risk is and how to manage 
it is not a simple matter.

/Janet L.

P.S. I'm the only diabetic in my family on either side
for at least 4 generations. But my father-in-law had
type 1 diabetes (onset late in life, possibly somehow
related to his Parkinson's Disease). I'm hesitant to 
mention this to people who don't already know because
they might think it's a reason that my husband and I 
should not have children together. (I don't think it is.)

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