Screening Embryos for Genetic Disease

November 2006
Written by Heather Walmsley

Tags: Health, screening, prenatal

Is Lucy healthy?
Lucy has always thought herself to be healthy and normal. When she first started school she hated it, because people laughed at her odd ‘tics’. Her face used to twist and her shoulders jerk forwards. Sometimes, before she realized she was doing it, she would shout the same word over and over. But slowly she learned to control this. And her classmates don’t notice it much anymore.

Her parents tell her that everyone is born with special gifts and burdens. So, while Lucy feels different, she also knows that difference is normal. Her friend Andrea has ‘dyslexia’ and struggles to read. Simon carries an inhaler, in case he has an asthma attack. John is good at math but wears thick glasses. Natalie is the fastest runner in the class, but the boys laugh at her big nose.

Is Lucy ‘healthy’? She has Tourette Syndrome – a neurological disorder with a genetic component. What about Simon? Three million Canadians have asthma. And John? And what about Natalie? A big nose runs in her family, and it certainly causes just as much emotional pain as Lucy’s condition causes her….

These are important questions because couples can now screen out certain inherited conditions in their children, during IVF (in-vitro fertilisation).

Screening for genetic ‘disease’
During IVF, a doctor removes a woman’s eggs from her ovaries and fertilizes them with her partner’s sperm in a laboratory. The fertilized eggs then divide into a small ball of cells and are implanted into the woman’s uterus.

Some IVF clinics now offer pre-implantation genetic diagnosis (PGD) too. This involves testing the DNA of embryos before implanting them – to check for evidence of serious inherited diseases such as cystic fibrosis, muscular dystrophy, sickle-cell anaemia, and Tay-Sachs.

PGD – right or wrong?
Some people think PGD is simply wrong. They believe that an embryo is not just ‘a bundle of cells’ but a very tiny baby, with the moral status of a human being. They argue that killing any embryo during IVF – even one with gene mutations – is immoral.

But PGD is practiced in many countries. Many people think it is a good thing – to prevent children being born into lives of suffering. For example, most children with Tay-Sachs disease cannot be treated. As fatty substances clog up the nerve ends in their brain, they become deaf, then blind, then unable to swallow, then paralyzed. Although the children are born normal, the disease progresses and most children die before they are four.

What do you think? Is it right to kill human embryos? Is it right for children (and parents) to suffer Tay-Sachs, if they can be spared the pain?

Where should we draw the line?
Right now, you might be thinking that ethics questions are pretty black and white….

Not really, because the list of genetic conditions that doctors are screening for with PGD is getting longer and longer. It’s hard to know where to draw the line.

In October 2005, a group of US scientists discovered a gene-mutation that causes some cases of Tourette Syndrome. If parents were able to screen for this gene mutation in the future, would it be a good thing? Think about Lucy. It’s hard not to agree that her life would be better if she didn’t have Tourette Syndrome. But would the world be a better place, if she hadn’t been born? Would the world be a better place if nobody got Tourette Syndrome?

Before you answer, consider that some people with Tourette’s do have really miserable lives, and find it impossible to make friends. Then again, some never even show symptoms. You should also know that Mozart is thought to have had this condition. Would the world have been better without one of the greatest composers that ever lived?

Valuing lives
It would be so much easier if we had some kind of machine – to measure which genetic lives were worth living, and which were not.

But this machine could never please everyone. Couples already reject embryos with markers for Muscular Dystrophy. They want to give their children a good start in life. But some disabled people find this insulting, as if their lives were worthless. After all, people with Muscular Dystrophy can achieve incredible things – like swimmer Danielle Camp who has set three world records.

If you had to decide, and the scientific possibilities were limitless, what genetic conditions or traits would you allow couples to screen for, using PGD?