Preimplantation Genetic Diagnosis and Single Gene Defects

Preimplantation genetic diagnosis (PGD) is recommended as a part of IVF treatment to couples when there is a fear of a genetic disorder being transmitted to the embryo. Preimplantation genetic diagnosis is recommended when one or both of the parents is a carrier of a genetic abnormality. The embryonic testing done as a part of PGD ensures that embryos carrying or indicating to be carriers of a genetic abnormality are systematically eliminated. This ensures that only the healthiest of embryos are implanted into the IVF female. Among various genetic disorders decoded through PGD, single gene defects are counted among the most serious and difficult to identify conditions.

About Single Gene Defects

As the term suggests, a single gene defect is essentially a genetic condition induced by a mutation or alteration in only one gene of the DNA. This gene could be present in the IVF male or female. People who have a history of single gene disorders in their family pose a greater likelihood of transmitting these genetic conditions to their children. Conditions caused by single gene defects include:

  • Sickle Cell Anemia
  • Tay-Sachs Disease
  • Cystic Fibrosis
  • Myotonic Dystrophy
  • Duchenne/Becker Muscular Dystrophy
  • Cystic Fibrosis
  • B-Thalassemia
  • Huntington's disease

Effectiveness of PGD

PGD uses a method called Polymerase Chain Reaction or PCR testing for decoding the single gene defects. In an overall perspective, PGD is considered capable of identifying single gene defects in most of the embryos. However, this doesn't mean that embryos tested through PGD cannot develop single gene defects. Due to the technical limitations, some degree of inaccuracy of results is indicated. PGD has been found useful for decoding three main types of single gene defects. These have been classified as:

  • Autosomal recessive genetic disorders
  • Autosomal dominant genetic disorders
  • X-linked genetic disorders

The only other alternatives to PGD testing are post-conception procedures like amniocentesis and chorionic villus sampling that are not preferred by many people. These tests can be conducted only when the pregnancy has initiated. If single gene defects are discovered through these two tests, termination of pregnancy or giving birth to a child with genetic defects are the only options. In comparison, PGD allows elimination of embryos with single gene defects before conception.

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