Single Gene Disorders
About PGD for Single Gene Disorders
Single gene disorders are genetic conditions caused by the alteration or mutation of a specific gene. Single gene disorders are often heritable (run in families), and therefore, individuals with a family history of a single gene disorder may be at risk for passing the condition onto their children. Examples of single gene disorders include cystic fibrosis, sickle cell anemia, Tay-Sachs disease, myotonic dystrophy, Duchenne muscular dystrophy, Fragile X syndrome and spinal muscular atrophy.
Single Gene Disorder FAQ
What single gene disorders can be tested?
RGI can perform PGD for essentially any single gene disorder for which the gene change (mutation) is known, including very rare conditions. Below, we have listed the single gene disorders for which RGI has previously performed PGD. It should be noted that RGI is always adding to this list, and if the disease you are interested in testing by PGD is not listed, we are happy to review your genetic report to determine if PGD is feasible.
RGI now offers discounted fees for certain single gene disorders.
How can PGD for single gene disorders help my family?
PGD is able to distinguish between embryos that are affected with a genetic disease and those that are not. Currently, PGD is the only way to determine whether an embryo is affected with a genetic condition prior to pregnancy. PGD has been utilized by many couples wishing to greatly reduce the risk of having a child with a devastating genetic disorder, and reduces the chance that a family will need to make a difficult decision about terminating a pregnancy following abnormal prenatal test results.
How does RGI test for single gene disorders?
Testing a single cell from an embryo is very different from testing a child or adult for a genetic condition. Due to the limited amount of DNA that is available in a single cell, an individualized testing system (“PGD set-up”) is developed for each couple before they begin their IVF cycle. Creating the PGD set-up requires a DNA sample from each partner and may require additional DNA samples from family members. Our genetic counselors will inform you of the samples that would be required for your case, as well as the cost and time required for RGI to complete the PGD set-up.
Once the set-up is completed, PGD for single gene disorders can be performed by analysis of polar bodies, blastomeres, or blastocyst/trophectoderm. Sometimes, a combination of multiple biopsy and testing methods is used to increase the accuracy of the test. RGI’s genetic counselors will work with you and your physician to determine the optimal testing strategy for your case.
The cells that are biopsied are analyzed using a technique called polymerase chain reaction (PCR). PCR allows the laboratory to use a small amount of DNA to obtain rapid and accurate results. In addition to testing for a known gene change (mutation), RGI uses DNA “linked markers”, which is a method similar to DNA fingerprinting. Testing for linked markers in addition to a known genetic mutation allows for several ways to determine which gene is inherited by an egg or embryo (i.e. a healthy gene or an affected one). Using linked markers greatly increases the accuracy of PGD, as well as the ability to obtain a test result for each tested sample.
Intracytoplasmic sperm injection (ICSI) is required when PGD is performed for single gene disorders. ICSI is a technique in which a single sperm is injected directly into a mature egg, for the purpose of fertilization. When performing PGD for single gene disorders, ICSI is required in order to greatly reduce the risk of sperm contamination of the cells tested. Without the use of ICSI, the laboratory may incorrectly test DNA from excess sperm that had surrounded the egg at the time of fertilization (instead of the DNA from the embryo), leading to misdiagnosis of the embryo.
What is the accuracy of the testing?
Typically, the accuracy of PGD for a single gene disorder is between 95-98%. The accuracy of the testing may vary depending upon the genetic condition, the cell type, and the number of linked markers for the family. In addition, the accuracy may vary from embryo to embryo within a given cycle.