Charcot-Marie-Tooth disease, X-linked (GJB1-related)

Charcot-Marie-Tooth disease (CMT) are a group of conditions that affect the nerves that connect the brain and spinal cord to muscles and to cells that detect sensations, such as pain, heat and sound (peripheral nerves). The symptoms experienced by people with CMT can vary signifcantly from mild to severe and may include effects on movement and hearing.

Individuals with GJB1-related CMT usually develop peripheral nerve damage between the ages of 5 and 25. This can including weakness and loss of sensation in the feet and ankles, making movement more difficult. Some individuals also have sensorineural hearing loss or nervous system symptoms. Symptoms tend to get worse over many years, with long periods of no noticeable changes. Intelligence and life span are normal. Treatment is focused on managing the individual's symptoms.

GJB1-related CMT is considered to be X-linked dominant. This means that a single GJB1 variant is sufficient to cause CMT in both males and females. However, females are more likely to have more mild symptoms than males, beacuse they still have a functioning copy of the gene.

Quick facts about Charcot-Marie-Tooth disease, X-linked (GJB1-related)
Genes: GJB1
Inheritance: X-linked
Relevant resources for Charcot-Marie-Tooth disease, X-linked (GJB1-related)

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 Charcot-Marie-Tooth disease, X-linked (GJB1-related) inherited?

Charcot-Marie-Tooth disease, X-linked (GJB1-related) 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 Charcot-Marie-Tooth disease, X-linked (GJB1-related), 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 Charcot-Marie-Tooth disease, X-linked (GJB1-related) before or early in pregnancy?

The biggest benefit of screening for Charcot-Marie-Tooth disease, X-linked (GJB1-related) 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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