May is National Huntington’s disease awareness month. RSC New England fertility doctor Kristen Wright, MD discusses how in vitro fertilization with preimplantation genetic diagnosis may help those with the disease prevent passing it on to their children.
untington’s disease is a hereditary, degenerative brain disorder for which there is, at present, no cure. HD slowly diminishes the affected individual’s ability to walk, talk and reason. Eventually, the person with HD becomes totally dependent upon others for his or her care. Huntington’s Disease profoundly affects the lives of entire families — emotionally, socially and economically.
Many individuals with a family history of Huntington’s disease wish to avoid passing on this disease to their children. Individuals who have Huntington’s disease, or who carry a gene for the disease, have a 50% chance of their child inheriting Huntington’s. Fortunately, according to Reproductive Endocrinologist Kristen Wright, MD, there is an option to screen embryos for Huntington’s disease before an embryo implants in the womb to establish a pregnancy. This involves performing in vitro fertilization (IVF) combined with a process calledpreimplantation genetic diagnosis (PGD), which allows an embryo to be tested for specific genetic diseases.
An IVF/PGD cycle typically includes the following steps or procedures:
- Genetic testing of the affected parent to determine the exact genetic mutation that is present
- Medications to stimulate a woman to grow multiple eggs
- Retrieval of eggs from the ovaries
- Insemination of eggs with sperm usingintracytoplasmic sperm injection (ICSI), a process in which a sperm is injected directly into an egg
- Culture within an embryology laboratory of resulting fertilized eggs or embryos
- Biopsy of one or a few of the cells from each embryo for genetic analysis
- Genetic testing of biopsied cell(s) from each embryo for the specific genetic mutation(s) that the parents carry, to determine which embryo(s) is/are unaffected, and which is/are affected, by the genetic disease being tested for
- Placement, or transfer, of one or more unaffected embryos back into the uterus when the genetic status of the biopsied embryos has been determined
- Support of the uterine lining with hormones to permit and sustain pregnancy
“The probability of becoming pregnant with a fetus affected by Huntington’s disease is much less after PGD testing than it is after natural conception,” explains Dr. Kristen Wright of the Reproductive Science Center (RSC) of New England. However, Dr. Wright adds, this technique is not perfect.
According to Dr. Wright, “Up to 10% of embryos yield an inconclusive test result due to technical reasons. These embryos can still be transferred into the uterus, but may result in a fetus carrying Huntington’s disease. It is also possible that genetic testing will reveal that none of the embryos are unaffected by Huntington’s or that none of the embryos will develop normally while in the IVF laboratory. In these cases the embryo transfer will not be performed. Finally, there is no guarantee that a child will be unaffected by Huntington’s disease after IVF/PGD, although the chance is much less than after natural conception. For this reason, it is strongly recommended that patients who become pregnant undergo chorionic villi sampling (CVS) or amniocentesis during pregnancy to reveal whether the PGD analysis was correct. Genetic analysis after CVS and amniocentesis is more accurate than PGD because many more cells are available for analysis.”
“IVF has been used to help establish pregnancies since the mid-1970’s,” states Dr. Wright. “Today, approximately 1 to 3% of all babies born in developed countries are the result of an IVF conception. While this technique is widely used and generally very safe, there are small risks involved. The female patient may develop ovarian hyperstimulation syndrome or may have a surgical complication as a result of the egg retrieval. If more than one embryo is transferred into the uterus, a multiple gestation such as twins or more may develop. Multiple pregnancy is associated with a significant increased risk for preterm labor and delivery that can sometimes result in lifelong problems for the babies. For this reason, it is recommended that only one embryo be transferred back into the uterus in good prognosis patients,” states Dr. Wright.
The risks for multiple pregnancy are greatly reduced at RSC New England which, according to data provided by the Society for Assisted Reproductive Technology (SART), has an average singleton birth rate of 84.2% among IVF patients. This most recent data released for 2011, indicates that RSC New England has the highest average singleton and lowest average multiple birth rate in New Hampshire, Rhode Island and Greater Boston.
“It is a tremendous relief for many parents affected by Huntington’s disease to know that their children will not be affected by this disease,” explains Dr. Wright. More information about IVF and PGD can be found on theReproductive Science Center of New England’s website.
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