Adrenoleukodystrophy (ALD) is a genetic disorder that affects the protein sheath that coats and insulates nerve fibers. Without this protein coat, nerve fibers are not able to send clear messages to and from the brain. Patients with ALD begin showing symptoms in early childhood, but by the time the disease has been diagnosed, it may be too late for treatment.
What causes ALD?
ALD is caused by mutations in the ABCD1 gene that is situated on the X-chromosome (one of two sex-determining chromosomes). Because women have two X chromosomes, they rarely develop symptoms of the disease but can carry the disease-causing mutation, which they can pass to their children. Men, who have only one X chromosome, develop the disease if they inherit a disease-causing mutation.
Women who are carriers of the mutated ABCD1 gene have a 50 percent risk of passing the mutation to their children. If they do and the child is a girl, she will be a carrier like her mother. If the child is a boy and has inherited the mutated X chromosome from his mother, he will develop the disease.
It is very important to diagnose ALD early because available treatments are only effective in a narrow window before symptoms appear, or very shortly after they do. Genetic testing can be used to confirm diagnosis and determine if other family members also carry the disease-causing mutation.
What is a genetic test?
A genetic test for ALD uses a blood or tissue sample from a patient to determine whether the patient’s X chromosome contains a disease-causing mutation within the ABCD1 gene. Genetic testing is usually used to confirm a diagnosis of ALD.
How is a genetic test performed?
A genetic test is usually performed on a small blood sample that is collected by a health professional at a hospital or clinic. The sample is then sent to a laboratory for analysis; DNA is isolated from the sample, and the specific region of the X chromosome containing the ABCD1 gene is sequenced, or “read,” to determine whether disease-causing mutations are present.
Following a diagnosis, other people in the patient’s family may also undergo genetic testing to determine whether they have the disease-causing mutation as well, regardless of whether they have symptoms.
During pregnancy, amniocentesis and chorionic villus sampling (two tests that can detect abnormalities) can both be used to test for the genetic mutation, but only if the physician or technician is specifically looking for it.
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