Preimplantation Genetic Diagnosis for Adrenoleukodystrophy

Preimplantation Genetic Diagnosis for Adrenoleukodystrophy

If you and your partner are both carriers for adrenoleukodystrophy (ALD), or if one of you has a type of ALD (such as adrenomyeloneuropathy (AMN) or Addison’s disease), you may be interested in reducing the risk of your children inheriting ALD by pursuing in vitro fertilization (IVF) with preimplantation genetic diagnosis instead of conceiving naturally.

How do children inherit ALD?

The mutation that causes all types of ALD affects the ABCD1 gene that is located on the X chromosome, one of two chromosomes that determine biological gender. Men have one X and one Y chromosome, while women have two X chromosomes. If a man inherits a mutated copy of the ABCD1 gene from his mother, he will develop a form of ALD. However, if a woman inherits an X chromosome carrying the mutated gene she usually has only a few symptoms because the healthy gene on her other X chromosome can compensate.

Women rarely inherit two mutated copies of the ABCD1 gene, but it can happen. Researchers identified more than 650 mutations that cause different types of ALD. If patients are able to make some ABCD1 protein, even if it doesn’t work as well as it should, they may have AMN or Addison’s disease; but if no protein can be made from the gene, the more severe form of the disease usually is present. This childhood-onset form of the disease (CALD) is more severe, and most children do not live to adulthood. It usually is not possible to predict from a particular ABCD1 gene mutation how severe the disease will be, or how it will progress.

A small percentage of CALD cases occur as a result of novel mutations in patients with no family history of the disease. For patients who inherit an ABCD1 mutation, the progression of the disease may be different from what the child’s parents had. For example, if a child’s mother has AMN or no symptoms of the disease, the child still might have CALD.

What is preimplantation genetic diagnosis?

Instead of conceiving naturally, parents can have their sperm and egg combined in a laboratory to create embryos. Doctors can implant these embryos into the mother’s (or a surrogate’s) uterus. This process is called in vitro fertilization.

Clinicians can screen embryos created by IVF for genetic problems before doctors implant them. They collect a few cells from each embryo and use these for genetic testing. They safely freeze the embryos until the test results are back. This process may take a week or two. Parents can choose to implant only embryos that do not contain a mutation in the ABCD1 gene.

Your doctor will discuss with you how you want to proceed at each stage of the process.

Benefits of preimplantation genetic diagnosis

Preimplantation genetic diagnosis greatly reduces the risk of transmitting a genetic disease to the next generation. Because clinicians perform the procedure before implanting the embryos, parents can decide whether to proceed with a pregnancy.

Concerns about preimplantation genetic diagnosis?

Preimplantation diagnosis helps reduce your risk of passing adrenoleukodystrophy or another genetic disease to your children. However, it cannot eliminate the risk completely. This is because sometimes adrenoleukodystrophy develops as a result of new mutations that occur during early development. You should discuss with your doctor whether additional prenatal diagnosis tests will be needed.


Last updated: July 15, 2020


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