Tag Archives: Huntington Disease

Screening – part II

In my previous post I wrote about the kinds of screening that could be though of as what you get for having reached a certain age (eg, age 50 for colonoscopy/colon cancer screening) or age +/- behaviors (eg, a sexually active female above a certain age). In future posts I might write about a particular screening test in more depth.

However in this post I’d like to talk about screening for genetic diseases. This is a bit different that the screening I wrote about last time and people can fall into several groups. One group is to see if someone will develop a disease. One disease that fits this mold is Huntington’s Chorea. People who have the mutation do  go on to develop the disease. For Huntington’s Chorea there needs to be a clear family history for testing. For Huntington’s, as well as well as other’s like it, there are multiple things to consider before testing. A big consideration  for Huntington’s Chorea is how one would handle the information if one was found to have the disease (there is no asymptomatic carrier state the same way there is for tay sachs, sickle cell anemia and others). Either you have the mutation and will develop the disease or you don’t and won’t. Someone might choose only to get tested if there is a chance they will have kids and want to know the chances of passing the disease onto their children, or to do prenatal testing, which brings up a whole lot of other issues beyond the scope of this post (what would you do if the test was positive? would you end the pregnancy? Would you go forward knowing you and the child you bring into the world would develop the disease? Would you get tested or do prenatal testing of the child if you were against ending the pregnancy? If you get tested before pregnancy and are positive, would you decide not to have children or would you do some sort of pre-implantation diagnostic testing and then only implant embryos that are free of the disease  – this latter approach might not be something insurance covers which is a whole other discussion/set of issues). Another disorder that fits into this category is Familial Polyposis Coli.  People who inherit this disorder have a virtually 100% chance of developing colon cancer and have an average age of 39 at the time of diagnosis of colon cancer. There are a few mutations associated with this disease which give rise to a somewhat different course of disease (mainly in the average age of diagnosis, # of polyps, etc). To my knowledge the best diagnostic tests for this are family history and colonoscopy rather than genetic testing – it allows for biopsy, quantification of the # of polyps, etc). In this case testing for the disease poses fewer of the issues than say, Huntington’s as there is a treatment available for this disease. If or when there is a treatment for Huntington’s chorea, then some some of the thornier issues mentioned above change.

This brings us to the next group – screening for a carrier state. What disorders one screens/gets screened for depends on one’s family history as people from different parts of the world are at risk for different diseases. Examples of disorders I am thinking of include Sickle Cell Anemia, any of the Thallessemias (and there are several. Some are lethal if inherited. Others are lethal or more symptomatic if two forms are interited together) If one is free (as best as genetic testing can tell), one’s partner might still want to be tested. Their children might not be at risk but grandchildren might and knowing that risk can be helpful. If both partners carry the trait for a particular disease several options exist. Some I mention above (testing pre implantation genetic diagnosis, aka PGD), deciding not to have children, etc. How one might choose to use the information is a matter of conscience.

In the last group of screening, it is to assess whether one is at risk for developing diseases where family history of suggestive of high risk: testing for BRAC1 and BRAC2 mutations in people whose family history includes a high incidence of breast and/or ovarian cancer, for example. This group is similar to the first one. Family history can guide if someone’s high risk. It is unlikely a clinical geneticist would screen for Huntington’s in someone with no family history whatsoever. If the family history shows only sporadic cases of breast or ovarian cancer, for example, testing for BRAC1 and BRAC2 would be less helpful. In these cases it is the person him/herself who’s at risk for the disease.  With some tests such as for BRAC1 and 2, the risk of disease may not be 100%, as it is with Huntington’s. In cases testing, some can decide about, say prophylactic mastectomy and/or oophorectomy, whether to wait after one has had children, etc. Of note, even if the risk is for typically a “womens’ disease” and the risk is on a father’s side of the family it is worth testing for.

Some last thoughts on this issue. If one is thinking of doing any sort of genetic testing, a primary care physician is a good place to start as he or she will at least be able to give some input on how likely one has a hereditary syndrome running in the family. However for actual testing it’s better to go through a clinical geneticist for testing. They have the background to pre and post test counseling.  The clinical geneticist will also be be set up with a lab that would do the testing, as even in a tertiary care center, the laboratories that do the testing are more specialized than  those that do the routine testing physicians do.

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