Ethical issues associated with PGD for inherited cancer susceptibility



This is because of a combination of several factors:


? they are lower-penetrance (i.e. not everyone with the faulty gene will develop the cancer);
? the occurrence of cancers have a later age of onset ? in adult life in many cases;
? there is a possibility for preventative surgery, early detection and effective treatment for these
cancers in susceptible individuals.

 

Penetrance: The penetrance of a condition determines the proportion of people who carry a copy of a faulty gene that will be affected by a condition. If a condition is 100 per cent (or fully) penetrant, every person who carries a faulty gene will develop the condition. If a condition is 50 per cent penetrant, half of the people that carry a faulty gene will go on to develop the condition.
The penetrance for cancer development of the conditions we are considering here varies from around 30 per cent to 80 per cent depending on the condition or the fault within the gene. Carriers of these genes therefore have a strong likelihood, or predisposition, to developing cancer but not a certainty.

Age of onset: This refers to the age at which symptoms of the genetic condition are seen. The majority of conditions for which PGD have been performed cause illness in the baby when it is born or in childhood. If a person inherits a faulty gene that causes a predisposition to cancer, the person is not likely to be affected by this condition until they are in their late thirties, forties or fifties.

The potential for preventative surgery, early detection and effective treatment: Although there are treatment options for many of the conditions, for example cystic fibrosis, these are usually for the relief of symptoms rather than providing a cure. For people who develop cancer it is possible to be treated with drugs and/or surgery. Many people are successfully treated for cancer and this number is increasing as better treatments are developed. It is also possible for people who know that they are at risk to have regular checks and/or preventative ? prophylactic ? surgery to remove tissue that is likely to be affected by cancer such as the breasts (mastectomy) or bowel (colectomy). These are difficult decisions to make because there is a chance that the cancer may not develop, and if it does, it could be treated.

As couples present for PGD of heritable cancer, there is likely to be widespread debate in the community about the associated ethical issues, including disposal of embryos carrying the cancer-predisposition gene mutation and the practice of eugenics.

The ethical issues surrounding PGD for heritable cancer are really no different from those for autosomal dominant late-onset disorders. The best example is Huntington?s disease where individuals with ?40 CAG repeats in the Huntington gene have many years of ?disease-free? life, but will ultimately develop neurological symptoms later in their lifetimes.

Like Huntington?s disease, the overall life experience of some individuals and families affected by inherited cancer syndromes is also profoundly difficult, not only from seeing family members suffer from the disease but also the anxiety about if and when they too will be affected.

The option of PGD can ensure that future generations of families who utilise this technology will not be faced by such difficulty. It also offers an option to couples who would find terminating a pregnancy for an adult-onset cancer predisposition syndrome unacceptable. Couples who choose to utilise PGD do not make this decision lightly. It can be a long, stressful and costly process, and only those who are committed to the outcome will persist with it.


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