Basic biology

Couples who have children with certain medical problems may be interested in PGD (preimplantation genetic diagnosis) for two reasons:

    • To facilitate the development of a baby that is free from the genetic condition

 

    • Create the opportunity to save the life of an existing child with an otherwise untreatable disorder

Some of the disorders that we have used this technology for:

    • Fanconi anemia

 

    • Thallasemia

 

    • Diamond-Blackfan anemia

 

    • Acute lymphoid leukemia

 

    • Acute myeloid leukemia

The thing that all these conditions have in common is that they can all be cured by bone marrow stem cell transplantation.

The transplant hurdle

Most people are aware that when a transplant is attempted, the recipient must take medications that will suppress their immune system. This reduces or avoids the chance that the transplant will be “rejected” by their immune system.

The problem with this is that the drugs also suppress some of the beneficial things the immune system does. A person taking immunosuppressive drugs is much more susceptible to infection and disease. In addition, they must stay on these medications for the rest of their lives or risk rejection.

How does the body “know” a transplant is present?

HLA markers are protein molecules that are located on the surface of almost all cells in the body. The immune system uses these HLA markers in recognizing cells that are your own (self) from those that are foreign (non-self). Nearly 600 different HLA molecules have been identified. HLA markers are inherited. There are six HLA markers that are looked at for transplantation purposes. Three are inherited from the mother, and three from the father.

HLA Matching

Without PGD, the most likely way to find a match between two people is among siblings.

There is a 25% chance that siblings will inherit the same genes from their parents. This would be considered a “perfect match.”
There is a 50% chance that siblings will be a “half match” to a sibling, and
There is a 25% chance that siblings will not share any HLA markers in common.

Therefore, there is a 75% chance that any time a couple conceives a baby, that the baby will not be a perfect match for the affected child. Simply trying to have more and more children in the hopes that a match occurs is not a very feasible option for most couples.

Through a blood test, we determine which HLA markers are present in the affected child. Using PCR (polymerase chain reaction) technology, we identify which embryos are a 100% HLA match. Those embryos are used to try to produce a pregnancy.

After birth

When the HLA matched child is born, stem cells can be easily harvested from the umbilical cord. These stem cells can then be used for a bone marrow transplant without the need for immunosuppressive medications. Thus, the affected child is cured. This means the affected child no longer needs any treatment for the condition and does not require treatment to suppress the immune system. The child can lead a healthy normal life.