By sola Ogundipe
Are you at risk for transmitting an inherited disease? Are you or your spouse living with a genetic disorder or both of you have the trait of a genetic disorder?
Are you currently unmarried but worried that your future children could potentially inherit a genetic disorder?
Worry no more because it is now possible to prevent transmission and inheritance of common and uncommon hereditary abnormalities such as Sickle Cell Disorder, Down Syndrome, albinism, cancer, cross-eye, deafness, blindness, mental retardation, etc., in children simply by screening the parents.
The chances of transmitting genetic disorders to your children can be completely eliminated through Preimplantation genetic testing that comprises Preimplantation Genetic Diagnosis (PGD)—a procedure used to help identify genetic defects within embryos; and Preimplantation Genetic Screening (PGS)—that helps identify abnormal number of chromosomes in the genes.
The goal of PGD/PGS is to prevent genetically-linked maladies from being passed on to the child. Both procedures increase the chance of selection of healthy embryos that will develop into healthy babies. If you’re a candidate for IVF, PGD/PGS might be just right for you. Now you can have a disease free baby.
According to an experienced Obstetrician & Gynaecololgist/Endocrinologist, Dr Abayomi Ajayi, genes are more accurate than fingerprinting because each human being has a unique genome sequence that is applicable to the embryo.
Ajayi who is the Medical Director, Nordica Fertility Centre, Lagos, Abuja & Asaba said scientists can now take a cell from the embryo, analyse it and be able to tell all the diseases that the embryo can be predisposed to in life.
In Ajayi’s view, the commonest reason in Nigeria for PGD/PGS is sex selection either for family balancing or to prevent some diseases carried in the Y chromosome (male specific). He added that couples who have had even 2-3 miscarriages though they produce good embryos might need it.”When people get married it is a gamble because they do not know what diseases they or their spouse is carrying. Certain diseases can be removed with PGD/PGS. When we do gene sequencing it can tell us if you are going to be prone to a disease even if you have not developed that disease. But it can enable you to start preventing it.
“With PGD/PGS, you can screen for so many disorders. We discovered is that there are some very rare diseases in Nigeria among normal people and it applies to the whole population. We have established that there are some people that carry particular diseases which they transmit to their offspring and so we can prevent these diseases and the scope of these diseases have been expanding. Today there are over 2,000 diseases that can be prevented by doing these tests, including breast cancer that is an inherited disorder.
There is a gene for breast cancer that has been isolated. Also, there are some babies that are going to be blind after a few years, with PGD/PGS, it is possible to prevent congenital blindness, deafness, Sickle Cell Disease, etc. We can also prevent Cystic fibrosis which is often believed not to be common in this part of the world, but now I’m beginning to be skeptical about this belief.”
Explaining further, Ajayi observed that when two people are predisposed to a disease (carriers), if they come together, they can produce a child that manifests the full disease. “Scientifically, for you to be a carrier of a disorder, some gene mutation must have occurred. I can tell you that all of us, as normal as we believe we are, are carriers of at least five to eight diseases. We do not manifest these diseases, but the problem comes when we marry another person that carries the same aberration.
“A typical example is Sickle Cell Disorder. When two persons with AS genotype get married, the transmission of the sickle cell gene is described as being autosomal recessive. You need two copies of the gene in order for the disease to manifest. So each time they have a baby, there is a 25-percent chance that the baby could have SS genotype.
“But some diseases are dominant and their inheritance is described as autosomal dominant. For this category, each time the carriers have a baby, there is a 50 per cent chance of that baby inheriting the disease. Therefore there needs to be a screening method to see that even if the two parties come together, their children would not have the diseases that both parties carry. That is how PGD evolved. PGS is a later addition.”
“When you have an abnormal child, it takes so much from you. It’s much better to prevent it. For instance, in male factor infertility when there is very bad sperm count, we now know that the embryo depends on the integrity of the sperm for its survival, so if you have very bad sperm you are likely to give very bad embryos, it is important to screen you with these procedures to ensure that the embryos you are transferring are normal.
“There are some abnormalities not even compatible with life. A lot of Edward’s Syndrome cases are in Nigeria. The condition is not compatible with life, but 30-40 percent of the babies with the Syndrome come out alive and they just die a few days after birth. The baby is born and you just wait for it to die. Nobody wants to go through all that so when women say they want to have a child at all cost even an abnormal one. It is the duty of the doctor to inform her so she can make informed decision.”
Ajayi said previous approaches to genetic screening was to take a sample from the baby while it is in the womb, but noted that the limitation with that method was that the woman had to be pregnant first and the baby already affected.
“But now because of advancements in genetics, we are able to screen you even when you are not married or pregnant to know the genetic aberrations that you carry so that if you want to get married, you do not marry another person who carries the same kind of aberration. This would ensure you are not predisposed to having a baby that would have the full blown disease.
“If the two of you carry the genes, we can also do tests even before you get pregnant, to make sure that the embryo that is transferred does not carry the disease. And when you are pregnant we can screen for the genetic diseases with non-invasive prenatal testing approaches such as amniocentesis.”
He said medical experts know that congenital abnormalities are quite common just that majority are not diagnosed. “Sometimes babies with congenital abnormalities die in the uterus. Because the number of autopsies that we do for such babies is low, we really need to start looking more at why babies die so that we can prevent a recurrence.
“We see there are lots of babies with chromosomal and congenital abnormalities. The ones we are looking at are those having structural abnormalities. Doctors in Nigeria are not looking at the chromosomal and genetic abnormalities, but now we need to begin looking at them.
“Very rare diseases can be screened now. We are now screening egg and sperm donors in Nordica because one of the questions recipients are asking about how sure we are that there would not be transfer of diseases during egg and sperm donation. So you must ask for it because it attracts a fee.
“What this is leading us into is personalized medicine. By the time we know what your gene sequencing is, we will know the drugs that can work for you. It will no longer be that everybody will require the same treatment. It is affordable, but depends on your priority.”
Ajayi said that in the first three months of life most of the pregnancy losses have genetic problems. “Majority of spontaneous abortions, about 70 percent, are not normal pregnancies. The abortion is nature’s way of ensuring that abnormal babies are not born. We are now also able to look at the product of conception or aborted fetuses and see if they have genetic problems because sometimes recurrent miscarriage may just be nature’s way of saying that the coming together of these two people and what they are producing has issues.
“If you can make the diagnosis, you can help them such that subsequently the embryo that they are going to be using is those that will be free subsequently from these diseases. Most of the time the two partners are carriers of a diagnosable disorder or one is manifesting the disease and you want to prevent it from being transmitted to the offspring.”
He said PGS screenings are to make sure that the embryos are normal and have the ability to become babies. “We said about 70 percent of pregnancies aborted in the first trimester are not normal. Among some of the commonest reasons are why they are not normal is because they have chromosomal anomalies. Once PGS can confirm that the chromosomes are 23 pairs, that embryo can become a baby.
“Most of the time, PGD and PGS are needed as they are doing different things. One helps the doctor to pick the embryos that would become healthy babies, while the second diagnoses diseases. They are not routine tests yet, for so many reasons one of which is cost.”
In his view, PGD is like the Ferrari of IVF. He noted that women above 37 need it because the chances of error in them are higher than in younger people.
“If a 42- year-old woman wants to use her eggs, it is possible but she should do this screening test. The way nature does it is that when you are below 35, about 70 percent of your eggs are capable of becoming babies, not that they cannot carry diseases.
“When you are about 40, about 80 percent of your eggs cannot become babies and that is why we say it gets more difficult as you age because at that point in time it is your egg reserves that remain.”