Embryonic genetic testing, or preimplantation genetic diagnosis, is being increasingly adopted by fertility clinics across the world. This is because IVF treatment provides the freedom of testing the embryos before they are implanted in the uterus of the IVF female. This provides the advantage of eradicating embryos before pregnancy is initiated, saving the IVF couple from the emotional trauma associated with terminating a pregnancy. This is the usual problem related with other genetic testing methods that use post-pregnancy testing methods. An appreciable part of PGD testing is its ability to decode sex-linked disorders.
Some of the genetic conditions are autosomal in nature. This means that they are caused due to an abnormality in the chromosomes, numbered 1 to 22. However, a grouping of chromosomes is called sex-linked chromosomes. This includes sex chromosomes, X and Y. A genetic defect in these chromosomes can cause a direct transmission of the condition to the child, or the child may become a passive carrier.
For instance, some of the sex-linked disorders are called X-linked recessive disorders. This means that they involve the X chromosome and are most likely to be present among boys only and almost never affect the females. This is why during PGD testing, decoding the sex of the embryos also becomes a critical requirement.
Sex-linked disorders that can be identified through PGD testing include Duchenne muscular dystrophy, which is a progressive mental retardation found only among boys, and hemophilia, which is a life-threatening condition that causes uncontrolled bleeding. Other examples of sex-linked disorders where PGD testing has proven to be effective include:
- Neuromuscular dystrophies
- Vitamin D resistant rickets
- Incontinentia Pigmenti (Bloch-Sulzberger syndrome)
- Rett syndrome