Preimplantation Genetic Diagnosis for Early-Onset Alzheimer’s Disease

Preimplantation Genetic Diagnosis for Early-Onset Alzheimer’s Disease

by Dr. Hsien-Hsien Lei
Posted October 1, 2007 in DNA Testing, DNA and Disease, Genetic Engineering

embryosThe UK Human Fertilisation and Embryology Authority has approved the use of preimplantation genetic diagnosis (PGD) to select embryos free of the gene for early-onset Alzheimer’s disease (AD). The couple who applied has a family history of the disease on the man’s side. His mother, grandmother, and two uncles all died from early-onset Alzheimer’s.

In 2002, researchers in Chicago performed the first PGD procedure for early-onset Alzheimer’s disease. Fifteen embryos were screened for the V717L mutation in the amyloid precursor protein (APP) gene which acts in a dominant fashion; only one copy of the genetic mutation is needed to cause early-onset Alzheimer’s. In this case, the mother carried the V717L mutation inherited from her father. One of her sisters and one of her brothers also had the disease. At the time, the Wellcome Trust Public Health Genetics Unit raised the following concern:

Considerable controversy surrounds this use of preimplantation genetic diagnosis. The issue is whether a woman who knows that she is likely to fall victim to dementia while still in her 30s, and so be unable to care for her child, has the right to choose to become a mother.

Dr. David King, director of Human Genetics Alerts – an independent public interest watchdog group in London that opposes the use of PGD for early-onset Alzheimer’s disease:

We can confidently expect science to find a cure for Alzheimer’s in the next 40 years.

I don’t believe that it is better never to have been born than to live a healthy life for 45 years and die from Alzheimer’s.

If we don’t want to slide down this slippery slope, we must restrict PGD to conditions that are fatal in early life.

As for the couple who has just been granted the use of PGD for early-onset Alzheimer’s, the potential father is the one with the family history. Yet, he does not know if he carries the APP V717L gene mutation. If he does carry the genetic mutation, he has a 50-50 chance of passing the mutation, and subsequently the disease, to his children.

Although I’m not questioning this couple’s very personal choice, I do wonder why they are going through PGD without knowing the potential father’s genetic status. If he tests negative, he can rest assured that his children most likely won’t develop early-onset Alzheimer’s and they would not have to go through PGD. However, if he tested positive, he’d be in the same situation of considering PGD. I understand the psychological implications of genetic testing, but what is the rationale behind this choice?

Would you choose PGD to select embryos free of a genetic mutation even if you didn’t know if you had the genetic mutation yourself and thus had no a priori knowledge of the probability of passing the genetic mutation on to your children?

via PHG Foundation
Photo: Early human embryos from Wellcome Images under Creative Commons

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(8 comments)


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8 Comments

Comment by David Bradley

There was research published just last week providing additional evidence that Alzheimer’s disease is actually the “third” form of diabetes.

http://www.eurekalert.org/pub_releases/2007-09/nu-dst092607.php

db

Thanks for the link, David.

 
 
Comment by Dana Waring Subscribed to comments via email

Hi Hsien,

While I can certainly understand why Dad would be frightened about his status, I don’t think I would use IVF w/ PGD unless I knew there was a definate risk. IVF with PGD is still a relatively new technology – with risks that may not yet be fully understood. Seems like a lot to put this potential child though, and also Mom who will go through the IVF procedure.

I am not convinced the level of government involvement in the UK is what is needed in the US, however, I do appreciate its effect of getting this debate into the public eye. I feel this family, as I am sure they feel like they are facing a number of imperfect and difficult options.

Dana, It’s not just the government in the UK that tries to maintain a tight grip on genetic technology. There are so many watchdogs here that it makes my head spin!

 
 
Comment by Barry Starr

What a weird story. As I was reading along I was wondering about the ethics of not letting an embryo that will develop Alzheimer’s 30 years down the road grow into an adult and then finding out the dad doesn’t even know if he is a carrier.

The dad should be tested if only for money’s sake. PGD is very expensive (is it covered in England?) and the positive result will tell him he is a carrier anyway. Seems like a costly way to determine his status!

I guess the broader question is whether to screen embryos for conditions like early onset Alzheimer’s or Huntington’s disease. Personally, I would probably screen any embryos I contributed to if I were a carrier just to deal with my own guilt. I would feel terrible about passing on a gene that would cause my child to die young if I could prevent it.

Barry, Weird indeed. I really don’t understand how they’ve gone along with the man’s decision not to be tested. The alternative to PGD would be to not have any children at all. Tough choices that in most cases would be limited by resources.

 
 
Comment by KathyF Subscribed to comments via email

Is the gene for early onset AD a 100% predictor of the disease? If so, that would explain his reluctance to be tested, to find out his fate–dying in the same way his mother did–at a time when he is enjoying life and looking forward to fatherhood. It would be unethical to require that he discover his gene status in order to become a father.

I’ve been reading a blog by a young woman who tested positive for HD, and is considering PGD. The cost is covered for HD in England, but she doesn’t know how many children it would cover, for how long, etc. So many questions! But thank goodness people have a choice now.

Thanks, Kathy. You raise an important point that most of us wouldn’t quite understand. For this particular genetic mutation, I believe that a carrier is almost guaranteed to develop early-onset Alzheimer’s. DNA technology has certainly brought about dilemmas that didn’t exist before. Choices are good and bad, I think.

 
 

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