Transcription:
Genetic Testing for Huntington’s Disease

Melanie Cole (Host): Welcome. Our topic today is genetic testing for Huntington's disease, and here to tell us about that is my guest, Dr. Danny Bega. He's a neurologist and the Clinical Director of the Huntington's Disease Clinic at Northwestern Memorial Hospital. Dr. Bega, let's start with a little definition. What is Huntington's disease, and how common is it?

Dr. Danny Bega, MD, MSCI (Guest): First of all, thank you for having me here. Huntington's disease is a degenerative disease of the brain that is inherited, and it's a relatively rare disease. About one in 10,000 to 20,000 people are affected by it, and what occurs is that the brain is deteriorating over time, particularly in areas that are involved in coordinating movement, cognition, as well as behavior and psychiatric function. And so it's sort of thought of as a triad of cognitive, motor, and psychiatric disease that progresses gradually over time, with the unfortunate key being that there's this heredity to it where it's passed off from one generation to the next with about a 50% chance of inheriting the disease.

Melanie: As you brought that up, it's known as the quintessential family disease. Tell us a little bit about how that's inherited.

Dr. Bega: So the inheritance pattern is what we call autosomal dominant, which means that we all know we get one copy of every gene from our mother and one from our father, and it only takes one abnormal copy in this case to cause the disease. And so people who get the disease inherit one abnormal mutation in this particular part of their DNA from either their mother or their father. And once they themselves have that mutation, they have one normal copy and one mutated copy, they can then have a 50% chance of passing on that mutated copy to any of their offspring.

Melanie: So then tell us about the hallmarks of it. When does it present itself? Can it be mistaken for Parkinson's or Alzheimer's if someone does not know that they carry this gene?

Dr. Bega: The way that this disease typically manifests is when people start to develop sort of aggravated movements or excessive, almost fidgeting type of movements that can occur anywhere in the body. Those are movements that are very different from what someone with Alzheimer's disease or Parkinson's disease would look like to a trained physician. Not to say that there isn't misdiagnoses out there, but a movement disorder specialist would easily be able to distinguish the type of movements that someone with Huntington's would have from diseases like- more common diseases like Parkinson's.

Now beyond that, people with the disease present with this gradually progressive decline in their cognitive abilities and eventually develop a dementia. We often think of Alzheimer's when we think of dementia. Alzheimer's is the most common kind of dementia, but Huntington's disease itself also comes with dementia, and the presentation is very different in that the age of onset, we typically think of Alzheimer's as being a disease of the elderly. With Huntington's disease, this is not a disease of the elderly. This is a disease that affects people earlier in life and the average age, when people start to develop symptoms, is around the mid-forties with a range. We see younger onset Huntington's even as early as the teenage years, which is more rare, and as old as into the seventies or eighties. But the typical person is somewhere between thirty and fifty when they start to develop symptoms, which is very different from something like Alzheimer's or Parkinson's typically.

And lastly, the psychiatric piece. There can be a lot of problems with irritability, with depression. There's unfortunately a high rate of suicide and suicide attempts with people with Huntington's, and so these behavioral components of the disease also set it apart from a lot of other neurological disease that we see.

Melanie: Before we speak about some of the goals of treatment and symptom management, Dr. Bega, who should get tested for this genetic mutation? Who should consider genetic testing, and should they speak with a genetic counselor?

Dr. Bega: That's a great question, and a complicated one. The most obvious reason to test is someone who is having symptoms and has a known family history of Huntington's disease, in order to confirm the suspected diagnosis in that person. But there are other indications where we may consider testing, in that people who are wanting to know if they will eventually get Huntington's disease because they know of a family history. So this is considered what we would call predictive testing, in asymptomatic individuals who are at risk because of a family member, which puts them at a 50% risk of having the gene, and they don't yet have symptoms, but they want to know if they will eventually develop symptoms.

And so this is an area that really requires a lot of expertise and counseling because it turns out that only about 10% of the people who are at risk for Huntington's choose to get tested, and the decision to get tested is very individual based on an individual person's beliefs and desires about reasons why they may want to get tested, and we have to approach that with sensitivity and we really have to educate people about the pros and cons of getting tested.

Things that we bring up with people is the potential for how that may affect their planning for their future, how that may affect planning for having a family, having children of their own. One very good reason to get tested is people who are planning to have children, and if they want to know about the risk for their own children, and potentially prevent passing on the mutated gene to their offspring, that's something that we can do in this day in age. So we can do prenatal testing with in vitro fertilization using pre-implantation testing. So when a sperm and egg fertilize and form an embryo, embryos can be tested for the gene, and embryos that test negative for the Huntington's gene can then be implanted. And so people who are at risk can guarantee, using that method, that they have offspring that don't have the Huntington's gene. So this is one area where it's important to consider getting tested or doing the pre-implantation testing.

With regard to the process, we usually actually have people talk to our genetic counselor over the phone before we even meet them if they're considering being tested. We want to educate people about the implications of the test result on things like life insurance, disability insurance, on long-term care insurance prior to testing. A lot of people don't know about how it may affect those things before they decide to get tested, and we do that even before we meet them. We do that over the phone with our genetic counselor.

Then when we meet them in person, we go over the implications of testing again. I meet with them myself, our genetic counselor again meets with them, and we go over what is the reason for wanting to get tested at this stage in their life? Is it, again, due to planning for family planning? Is it curiosity? Is it worry? What are the reasons?

We go into the pros and cons of testing, we go into how they would respond, how they would react if a test came back positive or negative. How they would live their life differently if a test came back positive or negative. These are really important things to go over before testing, getting a sense of their ability to handle the test result. And so I think this is a process- it's not so quick, but we have to go through it kind of thoughtfully in this way.

Melanie: Other than prenatal testing, what are some of the limitations or the risks of finding out that you do have this genetic mutation? What is it that they can actually do if they find out that they do have it?

Dr. Bega: In terms of treating the disease earlier because they find out early, unfortunately right now there isn't a medication that I can give someone who tests positive early on that would slow the onset of the disease or prevent the onset of the disease, which is a big reason that people have, for a long time, chosen- the majority of people have chosen not to know. If there's nothing I can do about it, why should I know?

We're in a bit of a different era today. We're in an era where research in Huntington's disease is- exciting is an understatement. I mean, we're really in an era where breakthroughs are being made, and in an era where we're testing out treatments that we're hopeful may slow down the disease in our lifetime. And so knowing today means potentially participating in clinical trials, it means potentially knowing about these treatments that may one day slow down the disease earlier in the process. And so this is a time where we really need to think hard about testing for that reason.

The prenatal testing is a very important part, as you mentioned. Planning for the future is important. Thinking about as a disease that can lead to disability, planning for things like long-term care insurance, and disability insurance, and these sorts of things can be useful to do, kind of to think thoughtfully about the future.

Some people, based on their test results, choose not to have children. Some people, based on their test results, choose to have children but to go through it in a way where they can make sure that their children don't get the disease. But some of it is just also about planning; planning for the type of job that someone is going into, and being able to plan for their family as well.

So there are a lot of reasons that people choose to get tested, but a lot of information they need I think ahead of time in preparation.

Melanie: Dr. Bega, wrap it up for us with your best advice and information and what you want people to know that might have a familial history of Huntington's disease, and genetic testing, and even the goals of treatment. Should they be told that this is what they have?

Dr. Bega: Well for people who are already suffering from this disease first of all should know that being seen at a center that has a multi-disciplinary approach to care is vital. In our center, every patient sees a neurologist, a neuro-psychiatrist, a genetic counselor, a social worker. It really takes this group of specialists with expertise in different aspects of the disease to take good care of someone with Huntington's, and it's really important to have that expertise.

For people who are at risk who have loved ones with Huntington's, it's important to realize that there really is hope for the coming years in Huntington's. I believe this is going to be a very different disease to manage and treat even a few years from now than it is today. The research is coming. It can never come fast enough for people who are at risk for the disease or are suffering from the disease, but it is happening. I do believe we're going to have drugs that slow down this disease in the coming years, and participating in research is vital, being connected to centers that provide education on Huntington's and opportunity to participate in research is vital. In terms of deciding to get tested, there's not a right or wrong answer for people who are at risk, but go to a place where you can get the genetic counseling, the education to make an educated decision about whether getting tested is right for you.

Melanie: Thank you so much, Dr. Bega, for being on with us today, for sharing your expertise, and explaining so very clearly the implications of genetic testing for Huntington's disease. It's really important information for people with a familial history to learn about and to hear from you. Thank you again for joining us. You're listening to Northwestern Medicine PodTalk. For more information on the latest advances in medicine, please visit www.NM.org. That's www.NM.org. This is Melanie Cole, thanks so much for listening.