Genetic diagnosis for healthier children a reality

Lynne Smit

It is all too easy to get caught up in the technicalities of genetic therapy, where the diagnosis of a disease by looking at a single gene on a microscopically small embryo can seem like magic to the uninformed. But as slide after slide of smiling parents with healthy children come up on the screen, it soon becomes clear that the miracle of birth is what the International Conference on Fertility and Sterility, IFFS 2007, last month, was all about.

For the couples who know that they could pass on a potentially fatal disease to their children, preimplantation genetic diagnosis (PGD) provides new hope.

Delegates heard how genetic diagnosis can be carried out on embryos to ensure as far as possible that they will not inherit the diseases carried by their parents. And it goes further than that: children are being born who hold the promise of a cure for their siblings already suffering from debilitating inherited diseases.

Its is perhaps fitting that in a session about heredity at a conference about fertility that Dr Oleg Verlinsky from the Reproductive Genetics Institute in Chicago was able to present a paper for his father Yuri who was recovering from an operation and unable to make the trip to Durban.

As he explained, PGD is not new. It has been 16 years since it was first used for sickle cell anaemia, and is now being applied to 130 genetic conditions. The difference now, he said, is that "as testing becomes more complex and accurate, the chances of implanting a healthy embryo become greater".

"New advances have also allowed doctors to determine that embryos that would have previously been considered normal were in fact carrying a risk for particular diseases or syndromes," Verlinsky said. "Now these embryos are not being implanted."

Dr Semra Kahraman, from the Instanbul Memorial Hospital in Turkey, explained how her institute is using PGD, not only to prevent the birth of affected children but also to conceive healthy babies who are potential donors of the bone marrow and umbilical stem cells needed to cure their siblings.

These embryos are tested not only for the presence or absence of a disease, but also for their human leucocyte antigen (HLA) compatibility. If siblings are HLA-identical, then there will be less chance that the immune system will identify the transplanted material as alien and thus attack or reject it.

Kahraman explained that parents are given extensive counseling so that they know that a cure is not guaranteed, even though in her experience all nine of the children treated with marrow of blood from their HLA-identical siblings at her hospital have been completely cured.

While Kahraman's work was mainly with children who had inherited diseases, Dr Karen Sermon from the Vrije Universiteit in Brussels is dealing with patients at a very different stage of their lives.

Her work is with late onset diseases, which often only occur after the patient has had four or more decades of normal life and normally affect several members of the same family.

These diseases are often not tested for, because patients were seen as having "a good life span" ahead of them before they started to become ill.

"Now that I am over 40 myself," she said "I don't see 40 years as being a good life span any more," she said.

Patients often come for testing because their parents or grandparents have begun to show symptoms of diseases like Huntington's or certain cancers. A complicating factor is that at least half of these patients are only interested in ensuring that their children are healthy, and do not want to know whether there is a time bomb of disease ticking in their own lives.

"This provides an ethical dilemma for health professionals," she said. "Often we are in the position of knowing that a patient is not a carrier, but we are forced to test and implant embryos in order to respect the patients' wish for nondisclosure."

 

June 2007