Fragile X syndrome

Fragile X syndrome causes a range of developmental and behavioural problems. People with Fragile X syndrome often have developmental delay, learning difficulties, anxiety and epilepsy, and are sometimes diagnosed as having features consistent with autism spectrum disorder. However, males are usually more severely affected than females because the FMR1 gene (which causes the condition) is located on the X-chromosome. Fragile X is the most common form of inherited intellectual disability.

Quick facts about fragile X syndrome
Genes: FMR1
Inheritance: X-linked
Alternative Names: Fragile X syndrome pre-mutation, FRAX, Fragile X
Relevant resources for fragile X syndrome

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 fragile X syndrome inherited?

fragile X syndrome 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 fragile X syndrome, 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 fragile X syndrome before or early in pregnancy?

The biggest benefit of screening for fragile X syndrome 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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