Genes are the basic building blocks of all living organisms. Contained within chromosomes, genes are the ‘data storage’ devices in cells that store information about the structure and function of cells. A defect in the genes disturbs the proper structure and hence, the function of the cells. These abnormalities are known as genetic disorders or genetic defects.
Chromosomes are microscopic, rod-shaped, structures that are found in the cells of living organisms. There are 46 individual chromosomes in each cell that are further grouped into 23 pairs.
Genetic defects in which there is a single identifiable defective gene are called single gene disorders. Fragile X syndrome and Huntington’s disease are some examples of single gene disorders.
During the process of IVF, there is a chance for abnormalities to arise in the number of genes in the embryo. Such embryos rarely implant successfully. If they do get implanted, it almost always leads to a miscarriage. However, despite the defects, some do implant successfully and the pregnancy is carried forward. Babies born of such a pregnancy have certain anomalies detected at birth.
Preimplantation genetic diagnosis
Developed in the late 1980s, preimplantation genetic diagnosis or PGD IVF tests fertilized embryos for single gene disorders. This is performed in order to prevent the implantation of genetically defective embryos during IVF. However, PGD IVF is limited in sensitivity as it can detect only 2% of the known genetic disorders.
What is Karyomapping?
A newer technique, Karyomapping is a single nucleotide polymorphism (SNP) test which examines the DNA of the parents and other close family members to identify a DNA fingerprint unique to the part of the chromosome that carries the mutated gene and which codes for the specific disease. This is then tested against the cells from the embryo to confirm that the gene mutation is not present. Karyomapping has the ability to identify all genetic defects.
How is Karyomapping different from other preimplantation genetic diagnosis tests?
PGD IVF tests, until the introduction of Karyomapping, had to be tailor-made for each couple. This required months of work and the wait was long and tedious. Conversely, Karyomapping is a universal test for all genetic disorders which reduces the waiting time to just a few weeks.
The Karyomapping procedure
An initial assessment is performed to identify whether you are a suitable candidate for Karyomapping. This assessment includes a detailed medical interview where your family history is examined closely for genetic defects.
DNA samples are collected either through saliva or blood. Samples from both partners and selected family members who carry the familial disorder are obtained in order to get a broader perspective of the situation.
The test examines the chromosomes of the parents, looking for the unique features of the defective gene. It is then possible to test embryos produced using IVF for the presence of this fingerprint.
Testing usually takes about 2 to 4 weeks depending on the information provided and to be gathered.
If the fingerprint characteristic of the chromosome carrying the defective gene is not detected, it can be inferred that the embryo has inherited normal copies of the gene and is therefore likely to be free of the disorder.
While these tests are being performed, the embryos are frozen and kept in stasis. Once it is established that the embryo does not have any genetic defects, it can be introduced into the mother’s uterus for implantation.
Does Karyomapping detect all chromosomal abnormalities?
Karyomapping uses the genetic make-up of the parents and affected relatives to identify any specific genetic mutations in the embryo with 95% accuracy. This process, however, cannot rule out genetic defects 100%. New mutations which might be absent in the parents but occur in the developing embryo cannot be detected through Karyomapping. It is recommended that couples undergo chorionic villus sampling or amniocentesis in order to detect any genetic defects that might have occurred after the pregnancy was established.