Study: Genetic Testing Not Good at Predicting Diseases

by Rebecca Taylor | Washington, DC | | 4/16/12 10:48 AM


If you have been reading this blog for any length of time you know that I despise genetic determinism. What exactly is genetic determinism? It is the unfortunate belief that we are no more than what is coded in our genes and that we can be evaluated as individuals accordingly.

I despise genetic determinism not simply because it reduces the dignity of a human person down to a sequence of nucleotides, but also because it is wrong scientifically. In reality, very few traits or diseases can be directly linked to a single gene variant or mutation. Some diseases are definitively linked to a specific problem in a gene or genes, examples would be Tay-Sachs, Sickle Cell Anemia, Cystic Fibrosis and Huntington’s. But the truth is that for most other diseases, it is just not that simple. Environment has as much or more to do with disease onset and progression as does genetics.

In fact, a recent study done by researchers at Johns Hopkins showed that genetic testing for disease is really not that predictive. They looked at occurrence of disease in identical twins and found that genetics were not a good predictor of who will suffer from what disease. From The Atlantic“:

The just-published study examines how often identical twins get the same diseases. Reviewing records of 53,666 identical twins in the United States, Sweden, Finland, Denmark, and Norway, researchers tabulated how well genes predict the chance of getting a disease. The answer is that they really can’t. Predictions based on genes turned out to be very close to useless. As Gina Kolata summed up in The New York Times: “While sequencing the entire DNA of individuals is proving fantastically useful in understanding diseases and finding new treatments, it is not a method that will, for the most part, predict a person’s medical future.”

And yet, at the same time utilitarian ethicists are continuing to push the idea that parents have the obligation to use IVF and preimplanatation genetic diagnosis (PGD) to have healthier children. In PGD, a single cell is taken from the early embryo and is tested for as many as 6000 different genetic variations. The embryos that make the genetic cut get a chance at being transferred to their mother’s womb. The others are discarded, donated to research or put in the deep freeze.

BioEdge reports that a new paper in the American Journal of Bioethics argues that parents are not just encouraged, but should be OBLIGED to use PGD to have “healthier” children. The title of the paper is “The Case for a Parental Duty to Use Preimplantation Genetic Diagnosis for Medical Benefit” and here is the abstract:

This article explores the possibility that there is a parental duty to use preimplantation genetic diagnosis (PGD) for the medical benefit of future children. Using one genetic disorder as a paradigmatic example, we find that such a duty can be supported in some situations on both ethical and legal grounds. Our analysis shows that an ethical case in favor of this position can be made when potential parents are aware that a possible future child is at substantial risk of inheriting a serious genetic condition. We further argue that a legal case for a duty to use PGD for medical benefit can be made in situations in which potential parents have chosen to conceive through in vitro fertilization and know that any children conceived are at substantial risk of having a serious genetic condition.

They argue there is a LEGAL obligation for parents who know they carry a serious genetic mutation to use PGD. Right now these ethicists argue an obligation to use PGD for a serious genetic condition, but as another utilitarian ethicist, Julian Savulescu, has already argued, some ethicists believe parents use of PGD should go beyond disease traits and be expanded to personality traits like intelligence as well.


Now realize that PGD chooses which children get to live based simply on their genetics. A criteria that the researchers at Johns Hopkins decided is not very predictive in disease. Which means genetics is not likely predictive in other personality traits like intelligence either. Environment is important in shaping a person both medically and socially.

But the IVF embryo has yet to experience much environment. It seems the utilitarian ethicist really doesn’t care. They want a nice neat genetic package with which they can arrange humanity into little boxes labeled “fit” and “unfit.” I think there was a pernicious movement of the early 20th century (starts with an E and ends in UGENICS) that did the same. Remember where that lead.

As The Atlantic points out:

We could clone Einstein and we really don’t know if he’s going to turn out to be an Einstein.

Remember gene expression the next time someone mentions an “innate musical talent,” or a “natural-born swimmer,” or “the math gene.” As a general rule, traits and diseases are developmental, not gene-determined.