Manipulating embryonic genes to avoid disease
Have you ever wondered what you or your children would look like with different colored eyes, hair or any other feature? More importantly, if you suffer from an inherited disorder, wouldn’t you wish you could save your offspring from suffering a similar fate?
Recent advances in reproductive technology have opened a gateway to screening embryos for genetic disorders, and selecting only those which are healthy, leading to the potential of eliminating a faulty gene in the family tree – forever.
With the recent successful sequencing of the human genome, (i.e identifying all the DNA that makes up our genes) genetic modification to select healthy embryos has become a promising prospect for many parents who carry genes that predispose their offspring to disease. This can involve replacing faulty sections of DNA from sperm, eggs or fertilized embryos with healthy sections of DNA, a procedure called germ line therapy.
In the past this has only been successfully carried out in animal embryos including monkeys. But it has shown that such procedures can carry untoward and unknown risks on the offspring’s physical and mental health, and that carrying out similar insertions in the human gene line is not at present an ethical option.
On the other hand, integrating healthy genes into the cells of children or adults has proved very successful in curing potentially fatal diseases such as cystic fibrosis, severe immunodeficiency (SCID) and Huntington’s disease.
Another method of genetic manipulation involves selecting embryos that lack the faulty gene. Last week British doctors in the UK announced that they are planning to create ‘designer babies’ free from inherited breast cancer. Four women with strong family histories of beast cancer will undergo intravenous fertilization (IVF) despite not suffering from fertility problems, in order to create “test tube babies free from a gene that would give them up to an 80 percent likelihood of developing breast cancer later in life. The procedure called Pre-implantation Genetic Diagnosis (PGD) involves using IVF to fertilize an egg and a sperm in a test tube (actually a Petri dish) to create several embryos, and taking cells from each embryo to test for genetic disorders; in this case the genes that predispose to developing breast cancer. The presence of these genes (called BRCA-1 and BRCA-2) in an embryo would lead to it being destroyed, and only an embryo lacking these genes would be implanted in the womb of the mother.
Screening embryos for genes that predispose to cancer is somewhat controversial as the women undergoing the IVF may not actually develop cancer themselves and furthermore, inherited breast cancer is a complex issue as it is an ‘adult onset genetic condition’ with people carrying the faulty gene not necessarily developing the disease. However, doctors argue that women who have lost relatives to breast cancer, should be given the chance to free their families from the disease and to eradicate the faulty gene from the family.
Can we also choose the sex of our baby? Yes. Determining the sex of an embryo is possible as the sperm used to fertilize the egg can also be genetically manipulated and chosen according to whether it carries a female or male determining gene. Thankfully, sex selection in most countries is only allowed in order to prevent diseases that are linked to a certain sex such as Duchenne muscular dystrophy and hemophilia, which are only expressed in male babies.
With the advent of such reproductive technology comes the danger of such technology falling into the wrong hands – people who would select for cosmetic, behavioral or other non disease traits akin to the ‘Frankenstien philosophy. PGD touches on many issues such as how disability is defined, the moral status of embryos, ethical issues and reproductive choice. It is up to each society, doctor, parent, to define the correct use of such technology, as misuse would be a crime to humanity, and could change our genetic constitution far beyond our human imagination; and even worse, beyond our human limitations.
Dr. May El Meleigyholds a Ph.D in Immunology from the London School of Hygiene and Tropical Medicine, as well as an MSc. (Toxicology/pathology) and a B.Sc in pharmacology) from London University. El Meleigy is a freelance medical/health writer and is currently producing Health Education programs for Egyptian TV.