Advanced IVF Lab Technique, Preimplantation Genetic Diagnosis or PGD, Identifies Single Gene Defects Prior to Embryo Transfer
Preimplantation Genetic Diagnosis, or PGD, in conjunction with IVF can provide life-altering results when a couple carries a gene for a specific genetic disorder. PGD is performed in an IVF cycle after egg retrieval and before embryo transfer to help identify affected embryos, unaffected embryos, and embryos are carriers of the disease in question.
Patients may know that they are at risk for certain genetic disorders, either because one partner in the couple has the disease or is a known carrier for a disease. Texas Fertility Center has worked with many couples who were asymptomatic carriers, and were unaware of their status prior to preconception testing. For example, one in 31 Americans, or 10 million people, is a symptomless carrier of cystic fibrosis.
A preconception genetic test analyzes a blood or saliva sample to search for the presence of single gene defects that can lead to devastating genetic disorders such as:
- Cystic fibrosis
- Sickle cell disease
- Muscular dystrophy
- Polycystic kidney
Preconception Testing Precedes PGD
Couples can have their chromosomes evaluated in order to determine if they contain alleles
PGD allows for chromosomal testing and selection and transfer of unaffected embryos to avoid passing on inherited disease to your children or having a child affected by aneuploidy.
If the test confirms that one or both members of the couple contain an abnormal gene, the reference genetics lab utilizes either a known probe or genetic material from the couple’s blood to create a genetic probe specific to the condition that they carry. This probe is then combined with 6-8 cells removed from each healthy appearing Day 5, 6, or 7 embryo obtained from IVF in order to determine if the embryo has the abnormality. Most of the diseases that we screen for with PGD are called “autosomal recessive” disorders. This means that, for an individual to actually have the disease, both genes (one from the mother and one from the father) must be abnormal. In this case, the baby is said to be “affected” (ie. he/she has the disease in question). Babies that have one normal and one abnormal gene are “carriers” (ie. they typically do not display any symptoms of the disease – just like their parents). One exception to this is sickle cell disease, where carriers – known as individuals with sickle cell trait – can have symptoms.
PGD is also helpful for an individual who is genetically normal but may have a balanced translocation of their chromosomes. In this situation, parts of two unrelated chromosomes may trade places with each other, potentially resulting in embryos that contain either too much or too little DNA. As with single gene defects, PGD allows for the identification of these “unbalanced” translocations prior to the actual embryo transfer, avoiding the likelihood of transferring embryos that will either not implant or subsequently miscarry.