Sunday, May 10, 2009

Clarification On Genetic Testing

I belong to the HCMA forum for Hypertrophic Cardiomyopathy. I received some replies to a post I made back when I got my test results.

Did you know what your Dad's HCM gene was? If not, then your doctor cannot know that you didn't inherit this from your father and that you can't pass it along. In order for him to make this statement, your Dad would have to have known that he had a particular genetic mutation, and then if your sample didn't match his mutation, then you might still have a different HCM mutation.

I think that your doctor is misunderstanding the report. What it probably said is that you don't have any currently identified gene that causes HCM. If that is true, you might still have a gene that has not been identified yet as a gene that causes HCM. Nevertheless, you could still pass along a gene that has not been identified.
About 30% of the time the genetic testing for HCM will not turn up with a known mutation. That doesn't mean you don't have a familial form of HCM, just that it is not known. It also means that you could pass it on to your children, so an interpretation of the results of the genetic testing by somewhat who understands this is important.

We can only know if a gene you have is a copy of your father's by looking at your father's genes. Unless there is some tissue of his, or he was tested in the past, this didn't happen. If they reported -- as seems likely -- that you don't have any of the known mutations that tend to cause HCM, that doesn't mean there's no genetic basis for your disease, only that the genetic basis isn't known.
I had posted the results of the genes tested and the test interpretations and got this reply:

Yes, this says that you don't have any of the known variants (among the three genes they tested) that tend to cause HCM. There are other genes that have variants that are known to cause HCM. But even so, about 40% of HCM patients don't have any of the currently known variants. That means that (a) you have a lot of company, and (b) there is much about the pathways that lead to symptomatic HCM that still isn't understood. That said, you should know that there are actually very few diseases that have as well-known and strong a genetic basis as HCM.

Put differently: the "genetic tests" for HCM just ask a very simple question, namely, does this person have a mutation that we already know tends to cause HCM? If the answer is no, it doesn't say a thing about whether the person has a mutation somewhere else in the genome that tends to cause HCM.

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