D r. Abayomi Ajayi, Medical Director, Nordica Fertility Centre, Lagos, Asaba and Abuja, gives insight into the intricately sensitive procedure of PGD which he describes as the genetic profiling of embryos.
Preimplantation Genetic Diagnosis, PGD, is a procedure used prior to implantation to help identify genetic defects within embryos created through in vitro fertilization, IVF to prevent certain diseases or disorders from being passed on to the child.
In most cases, the female, male, or both partners have been genetically screened and identified to be carriers of potential problems. Knowing the genetic make- up of embryos mainly enables us to prevent the transmission of diseases that can be transmitted from parents to offspring.
This ranges from sickle cell to cancers anything that can be transmitted genetically. If it is a cancer that the gene sequence has been identified, then it can be prevented. Any disease whatsoever that the gene sequence has been identified can be prevented.
How it is performed
Begins with the normal process of in vitro fertilization that includes: ovary stimulation through medication, egg retrieval, and fertilization in a laboratory.
Over the next three days the embryo will divide into eight cells. The preimplantation genetic diagnosis involves a one or two cells are removed from the embryo.
Next, DNA is retrieved from the cell and copied through a process known as polymerase chain reaction, PCR. Finally, by molecular analysis, the DNA sequence code is evaluated to determine if the inheritance of a problematic gene is present.
Once the PGD procedure has been performed and embryos free of genetic problems have been identified, implantation will be attempted through embryo transfer, intracytoplasmic sperm injection, ICSI, or zygote intra-fallopian transfer, ZIFT.
Who can benefit
Any couple at risk for passing on a genetic disease or condition. Possible candidates include women aged 35 and over; carriers of sex-linked genetic disorders; carriers of single gene defects; those with chromosomal disorders and women experiencing recurring pregnancy loss associated with chromosomal concerns.
In this environment, the two common uses are for sickle cell prevention and genetic intervention of sex selection. PGD is beneficial to people with strong history of certain cancers such as breast cancer, and also Down Syndrome.
What PGD looks for
Genetic and chromosomal problems that increase risk for birth defects or spontaneous miscarriage are indicated. It identifies the presence of a large number of about 300 disorders.
Also looks for recessive sex-linked disorders such as haemophilia; dominant sex-linked disorders such as Rett syndrome, and vitamin D-resistant rickets; single gene disorders such as cystic fibrosis and sickle cell anemia.
PGD can be used to prevent diseases that come through genes or chromosomes and the mitochondria. Some disorders are recessive others are dominant.
We can look at all of them and look at the diseases that have been mapped out and exclude them from diseases not to be transmitted.
For recessive diseases, two abnormal copies are required to become manifest, e.g., sickle cell disease. One abnormal gene from one parent combines with another abnormal gene from the other parent to produce one SS child. In cancers that are dominant, only one abnormal copy is required for the baby to develop the cancer.
Fortunately there are other diseases such as cystic fibrosis that are not as common, diseases linked to the X chromosome. Selection is not only for gender balancing but to determine defective embryos. Babies are born free from diseases that can be transmitted from their parents.
Because the 23rd pair of chromosomes is the sex chromosomes, PGD can also determine the sex of the embryo and has been used for the purpose of gender selection.
In Nigeria and countries where there is preference for a specific gender. For instance, someone has many girls and wants a boy. Why not? If health is a state of physical, mental, and spiritual wellbeing, the man who says he wants to have a boy at all cost, should he not be enabled to do so? If the technique of PGD is the way to give him the desired boy, rather than marrying more wives and possibly having more girls, why not. I’m am not saying there are no ethical issues involved, but right now, the stage at which we are, we do not have problems of nations such as China or India. The issues on ground now are that we do not misuse PGD. There should be responsibility using the technique.
No dilemma, no risk
The beauty of PGD is that it prevents selective termination of pregnancy. In the effort of preventing transmission of genetic diseases to babies, the first major milestone was prenatal diagnosis where we can take a sample from the baby either through colonic biopsy or aminocentesis. The problem with this is that there is already a pregnancy. So you need to make a decision based on the result, whether to terminate or to allow the pregnancy to continue despite the fact that you know the baby is affected. But with PGD, that dilemma does not come in at all. You can pick out the affected embryos and implant only the good ones.