Genetic screening: too much information?

Thu, Feb 7, 2013, 00:00

OPINION: Genetic testing can detect thousands of medical conditions, but do you really want to know about them?

Like much new scientific technology, human genetic testing offers many advantages but also presents a considerable number of problems. This area bristles with ethical dilemmas for medicine. Parents and patients who embrace the new technology without caution risk burdening themselves with severe and unnecessary anxiety and fear.

The fundamental unit of biological organisation is the cell. Every human body contains about 50 trillion cells and each cell contains the full human genetic content (genome) in the form of the chemical DNA.

DNA is a very long molecule made of repeating units called nucleotides. There are four different nucleotides denoted by the four letters A, T, G and C.

The genetic DNA in every cell controls the day-to-day activities of the cell and is the hereditary material passed on to the daughter cells when the cell grows and divides in two. Prior to cell division, the DNA duplicates itself and identical copies are passed on to each daughter. The genetic instructions in DNA are encoded in the linear sequence of the four nucleotides A, T, G and C.

Mistakes can occur when the DNA copies itself, resulting in wrong information entering the coded instructions of the linear nucleotide sequence. Wrong information can also enter DNA for other reasons. Such wrong information is called a mutation, and it can cause a disease. Mutations are copied when the cell divides and they are passed on from generation to generation. A parent whose genome contains a mutation that predisposes for a disease can pass that mutation on to his or her child. The full human genome, containing about 3.2 billion nucleotides, was sequenced in a massive effort that culminated in 2003 at a cost of $2.7 billion (€1.9 billion).

Today, a person can have his or her individual genome sequenced from a teaspoon of blood for about $7,500 (€5,500), and the price is dropping fast. The individual genome sequence can be scanned for mutations that predispose for various diseases. Genetic screening can also be done on babies and on embryos in the womb. A wide variety of mutations can be screened for, including those that predispose towards or underlie Alzheimer's disease, colon cancer, breast cancer, diabetes, autism and obesity.

The advantage of this is that, for example, if genetic screening of your baby finds they are predisposed to develop Alzheimer's, you could steer them away from playing rugby, because trauma to the head could accelerate the Alzheimer's tendency. Similarly, a predisposition to develop some other conditions uncovered by screening could indicate protective dietary or exercise regimes.

On the other hand, what do you do if genetic screening of the baby shows up a mutation indicating that a neurological disease will develop in the early 40s, progressing rapidly to dementia and for which there is no treatment? This news will depress the parents, and the question arises: should the parents tell the child later on and destroy his or her peace of mind for the rest of their lucid life? Releasing the information will also mean the child can never get disability or long-term care insurance. A strong case can be made that it would be unethical to tell the child. Indeed, it might be better if the parents didn't know either.

Genetic testing can now detect over 2,500 medical conditions, but only about 500 of these are treatable. People often have genetic screening to try to shed light on a mystery illness or to check if they are carrying an unfortunate familial trait. But these powerful screenings often show up genetic results that were not looked for.

Most parents say they want to know about every risk of disease to their children even when there is no treatment. Majority medical and ethical opinion, however, favours sharing only genetic results that can be acted on immediately (The DNA Dilemma by Bonnie Rochman, Time, December 24th, 2012).

Genetic screening of the developing embryo is becoming increasingly common. If the embryo is diagnosed to be carrying a gene that predisposes towards a serious disease, the option to abort is often taken in countries where abortion is available. According to a New York Times article from May 2007, about 90 per cent of pregnant women given a Down syndrome diagnosis in America had chosen an abortion.

William Reville is an emeritus professor of biochemistry and public awareness of science officer at UCC.

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