Adrenoleukodystrophy (ALD) is a serious disease characterized by the progressive loss of the protein coat (myelin), which protects nerve cells from damage. ALD can also cause adrenal insufficiency where the adrenal glands fail to produce normal amounts of important hormones.
How ALD is inherited
ALD is caused by mutations in the ABCD1 gene, which provides instruction for making a protein called ALDP that is important in processing very long-chain fatty acids (VLCFAs). The mutation leads to little or no ALDP production, causing large quantities of VLCFAs to build up in the nervous system and blood, resulting in damage.
ALD is an X-linked disease, which means that the affected gene 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.
This means the disease affects mostly men because if they inherit a faulty copy of the gene with their only X chromosome, there is no other copy of the gene to compensate.
In women, a single copy of the disease-causing mutation generally does not cause the disease because the healthy copy of the gene on their other X chromosome can compensate. They are, however, said to be carriers of the disease and can pass it on to their children.
The son of a carrier woman has a 50 percent chance of inheriting the disease and 50 percent chance of not being affected, while her daughter has a 50 percent chance of being a carrier like her mother and 50 percent chance of not being affected.
For women who know they may be carriers (or that they may have inherited the disease-causing mutation), prenatal diagnosis can be used to determine whether their children are at risk of developing ALD.
What is prenatal diagnosis?
Prenatal diagnosis is the diagnosis of a genetic disease before a baby is born. It entails collecting a DNA sample from the fetus and analyzing it with genetic testing. In the case of ALD, the sample is used to look for mutations in the ABCD1 gene.
There are two main methods of safely collecting a DNA sample from the fetus: amniocentesis and chorionic villus sampling (CVS). Both procedures carry some risk for both mother and fetus. However, most patients only report a small amount of pain around needle injection sites for one to two days following the procedure. Depending on how many tests are being performed, it may take several weeks to get the results.
Amniocentesis is a procedure in which an ultrasound device is used to guide a needle through the abdomen to the uterus, allowing a small sample of amniotic fluid to be obtained, which contains a few cells shed from the fetus. These cells can be used for genetic testing.
CVS involves obtaining a sample of the chorionic villus, the wispy outgrowths of the placenta that contain fetal DNA. These samples can be obtained as early as 10 weeks into pregnancy by inserting a needle either through the abdomen (transabdominal) or through the cervix (transcervical). The samples can then be used for genetic tests.
What happens after testing?
Following testing, parents return to their clinic or hospital, and their physician or a genetic counselor will discuss the results of the tests, along with what options the parents have moving forward.
Adrenoleukodystrophy News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.