Adrenoleukodystrophy, X-linked

X-linked adrenoleukodystrophy (X-ALD) is a genetic condition that mostly affects males because the genetic variant for the condition is on the X chromosome. X-ALD affects the nervous system and the adrenal glands, which are small glands located on top of each kidney. In X-ALD, the myelin (fatty coating) that insulates nerves in the brain and spinal cord is prone to deterioration, which reduces the ability of the nerves to relay information to the brain. X-ALD can also cause damage to the outer layer of the adrenal glands which causes a shortage of certain hormones. Having a shortage of those hormones can cause weakness, weight loss, vomiting, and in severe cases, cause the person to experience a coma.

There are three distinct types of X-ALD that affect people in different ways and at different stages of their lives. X-ALD can affect each male who has the condition in different ways, even within the same family, and it is not possible to accurately predict the impact of X-ALD from a genetic result alone.

The cerebral form of X-ALD affects children and causes learning and behavioral problems. Over time the symptoms worsen, and the child may show aggressive behaviour, have difficulty communicating, and develop problems with their vision, swallowing, coordination and adrenal glands. It can be hard to predict how quickly the symtoms will get worse but sadly, children with this form of X-ALD will not usually survive more than a few years after their symptoms begin.

The adrenomyeloneuropathy form of X-ALD causes symptoms between early adulthood and middle age. People with this form of X-ALD develop progressive stiffness and weakness in their legs, experience urinary and genital tract disorders, and often show changes in behavior and thinking ability. Most people with this form also experience the problems regulating certain hormones and unfortunately, some people with this form have a shortened life expectancy.

The Addison disease only form of X-ALD can affect people at any age and starts with problems in the adrenal glands that affect hormone regulation. However, most people with this form will also experience symptoms of the adrenomyeloneuropathy type by the time they reach middle age. The Addison disease form is usally the mildest form of the condition however life expectancy depends on the severity of the signs and symptoms, and for some people, may still be shorter than average.

Quick facts about adrenoleukodystrophy, X-linked
Genes: ABCD1
Inheritance: X-linked
Relevant resources for adrenoleukodystrophy, X-linked

A quick genetics rundown

As humans we have about 23,000 genes. These genes are like tiny instruction manuals that influence our health, growth and development. We inherit half of our genes from our biological mum and the other half from our biological dad. These genes are lined up on structures called chromosomes. Most of us have 23 pairs of chromosomes. The first 22 pairs are called autosomes and for the most part - these are the same among men and women. The 23rd pair determine our sex - two X chromosomes for a female and one X and one Y chromosome for males.

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How is adrenoleukodystrophy, X-linked inherited?

adrenoleukodystrophy, X-linked is an X-linked condition. X-linked conditions occur when there is a genetic variation on the X-chromosome. For these conditions, the sex of the parent who passes on the gene variation influences the risk for the children.

If the father is affected, all his daughters will have a variation on one of their X-chromosomes and be healthy carriers. Sons can only inherit these x-linked conditions from their mother and therefore, in this situation, will not be affected by the disease.

If the mother is a healthy carrier of an X-linked variation and has a son, there is a 50% chance that they could inherit this variant and be affected by the disease. If they have a daughter, there is a 50% chance that they will be a healthy carrier (just like her mum).

Another way of looking at this is that there is a 25% chance of having an affected son and a 75% chance that the child will not be affected by the disease.

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What is carrier screening?

Carrier testing is like a checkup for your genes. It tests to see if you carry a gene variation that could cause a serious genetic disease in your child. Eugene offers an inclusive genetic carrier screening panel that includes adrenoleukodystrophy, X-linked, but there's a total 301 conditions that can be tested.

Eugene’s carrier test is a clinical grade test that can be done from the comfort of your own home — it’s just a saliva test. You're also paired with a genetic counsellor who provides mindful support and guidance every step of the way.

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Should parents screen for adrenoleukodystrophy, X-linked before or early in pregnancy?

The biggest benefit of screening for adrenoleukodystrophy, X-linked is that it can help future parents understand their reproductive risk so they can be ready and empowered to make more informed decisions. If neither partner are carriers, it provides reassurance and peace of mind that the risk of having a child with a genetic disease is low.

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