Mr Akeem Odunfa and his wife Mary have battled infertility for eight years. The husband is a 42-year-old albino; the wife is 33. Aside the challenge of infertility, they fear if Mrs Odunfa concieves, she may give birth to an albino.
They made their fears known at an uptown fertility clinic where they enrolled for fertility treatment. To their surprise, Dr. Ololade Oyetunji, a consultant in Obstetrics and Gynaecology at Nordica Fertility Centre that attended to them assured them that they could, have a child free of albinism or any inherited disorder. The couple did not disbelieve. They were counselled on how they could be helped.
Thirteen months after, they held their babies – triplets, and none had the disorder.
They can be described as being lucky, because to go through miscarriage after miscarriage, or to have an advanced pregnancy terminated because a significant abnormality has been found at pre-natal screening can be depressing.
So, how was this couple helped and how can syndrome such as stammering, blindness, deafness, ‘vitiligo’, Tuner syndrome, cancer, Down syndrome, sickle cell, among others be tackled before conception?
The Medical Director/Chief Executive Officer (CEO), Nordica Fertility Clinic, Dr Abayomi Ajayi said Nigeria has joined countries that can scientifically assist parents with the over 600 inherited diseases to avoid giving birth to babies with susceptible or confirmed inherited diseases. It is through pre-natal screening: pre-implantation genetic screening (PGS), but principally through pre-implanation genetic diagnosis (PGD). The two are involved in In-vitro Fertilisation (IVF).
Ajayi said to understand how inherited diseases are formed in babies through aneuploidy, one must understand that the nucleus of almost every cell in the human body has a chromosome make-up (or karyotype) of 23 pairs of chromosomes making a total of 46.
He explained: “Half of each pair of chromosomes is inherited from the mother and half from the father.The exceptions are mature red blood cells which do not contain a nucleus and eggs and sperm which only contain half the complement of chromosomes. The first 22 pairs of chromosomes are called autosomes while the 23rd pair are the sex chromosomes (X or Y). Every egg contains an X chromosome, while a sperm may carry either an X or Y chromosome. A female will have two X chromosomes and a male an X and a Y chromosome. The sex of an individual will therefore depend on whether an X bearing or Y bearing sperm fertilises the egg. A female has a 46XX karyotype and the male 46XY.
“Sometimes there can be an abnormal number of chromosomes in a cell. There may either be additional or missing chromosomes. This is known as aneuploidy and accounts for the majority of inherited disease syndromes. When there is an extra chromosome instead of a pair this is called trisomy. In a live birth, the commonest trisomy to occur among the 22 pairs of autosomes is trisomy 21 (Down syndrome). Trisomy can affect the sex chromosomes too: 47XYY (Klinefelter’s Syndrome). Autism is difficult to pinpoint and cannot be prevented for now because it has a multifacetness. Its cause has not been established. Monosomy is the term used when there is a missing half to a pair of chromosomes. An example of this is Turner’s syndrome where there is a missing sex chromosome (45X0).
“Rarely can there even be four or five copies of a chromosome. When there is aneuploidy, this does not necessarily affect every cell. This patchy distribution of unaffected and affected cells is called mosaicism. To complicate matters further, there can be partial aneuplody where there is a genetic imbalance caused by the addition or loss of only a part of a chromosome, a situation referred to as unbalanced translocation. Every other over 600 diseases that have been identified due to chromosomal abnormality can be prevented.”
And for PGD, Dr Ajayi said, “IVF is carried out as well. By the third day the embryo will contain six to eight cells (blastomeres). The embryologist removes one to two blastomeres for testing. Embryos that are found to carry the faulty gene that causes the specific inherited disease are allowed to perish/resolve. One to three embryos that are free from the genetic disorder can then be transferred. If there are any suitable additional tested embryos, these can be stored for future use by freezing.”
How precisely can this be done? Abayomi said it is through a simple clinical procedure, “It is possible to detect chromosomal abnormaities by analysing the pattern of chromosomes in cells. This is called karyotyping. There are a number of other refined techniques used in the genetic screening for aneuploidy, in particular Fluorescence Iin Situ Hybridisation (FISH), Comparative Genomic Hybridisation (CGH) and Quantitative Polymerase Chain Reaction (PCR).”
An Obstetrician and Gyneacologist, and member of Society of Gyneacologist and Obstetrician Society of Nigeria (SOGON), Lagos State Chapter, Dr Adebayo Bamisebi, shed more light on this. “In pregnancy it is possible to screen for aneuploidy by means of amniocentesis where a sample of the amniotic fluid around the baby is removed for FISH (i.e, a diagnostic tool) and karyotyping, and chorionic villus sampling where a small sample of tissue from the placenta is removed for testing. However there are a number of problems linked to such prenatal screening. These techniques are not without risk. Miscarriage can complicate these invasive tests and statistically when this shattering event happens it is far more likely to be a normal pregnancy that is lost than an affected one,” Bamisebi said.
They both agreed that while pre-natal screening or Pre-implantation Genetic Screening can detect those pregnancies affected by aneuploidy, PGD goes a step further by testing an embryo for specific inherited abnormalities/disorders.
According to Dr Tayo Abiara, an assisted reproductive health expert , “pre-implantation Genetic Screening (PGS) offer screening that avoid the transfer of embryos that have common chromosomal abnormalities. Unlike PGD, PGS is not looking for a specific but PGD is a technology used in conjunction with IVF to screen embryos for genetic conditions prior to transfer, so as to remove a cell from a three-day old embryo fertilised in vitro or analyse cells for specific genetic or chromosomal abnormalities.”
Bamisebi explained that some couples are at risk of having a child with a specific serious genetically inherited disease. Such a disease may be due to an abnormality affecting the genes, chromosomes or tiny structures within the cell called mitochondria. Couples may have become aware of this because: “There is a family history of a genetically inherited disease; you have a child with a genetically inherited disease; you have had terminations of pregnancy for a genetically inherited disease. Until recently, pre-natal testing (amniocentesis and chorionic villus sampling) offered the only means of diagnosing serious genetic conditions affecting the baby. When found, the distressing option of having the pregnancy terminated could then be considered.
“But PGD provides an alternative to prenatal screening as embryos can be tested for any one of over 50 serious inherited disorders. PGD checks the genetic makeup of embryos obtained through IVF so that only unaffected embryos are transferred. Through PGD, couples are able to avoid passing on the condition to their children,” explained Dr Ajayi.
Nordica’s Clinic Manager, Mrs Tola Ajayi explained that PGD offers a better chance to PGS because, “There are some genetic diseases inherited by children that are life threatening and can only be treated by using stem cells from a close member of the family. PGD takes care of that. PGD involves a multidisciplinary team, that include the clinic’s own reproductive medicine specialists, embryologists trained to carry out the necessary embryo biopsies, clinical genetics specialists, scientists and counsellors.”
And how is PGS done? Ajayi explained: “IVF is carried out in the normal way. By day three of the embryo will contain six to eight cells (blastomeres). The embryologist removes one blastomere for chromosome analysis using the FISH screening technique. Clinics will screen five to 10 specific chromosomes of the 24 chromosomes, looking for the commonest chromosome disorders.
“Embryos that are free from chromosome abnormality can then be transferred. A maximum of two screened embryos can be transferred regardless of the age of the woman. If there are any suitable additional screened embryos these can then be stored for future use by freezing.”