What is Fragile X syndrome?IN BRIEF
Autistic people are more likely than others to have Fragile X syndrome (FXS). It's a genetic difference. In general, people who have fragile x syndrome need a lot of support. This can result in individuals having a particular type of facial appearance, but you would have to be familiar with the condition to notice this difference.

Definition of Fragile X syndrome?
It is a series of mutations located on the X chromosome, one of the human sex chromosomes. People with Fragile X syndrome often have distinct facial features, atypical intellectual development, and attention deficits. Everyone has at least one X chromosome. However, people with a single X chromosome and the associated syndrome (mostly boys and men) need a lot of support. However, some people show almost no symptoms.
Link to autism
Symptoms
- Delayed intellectual development
- Difficulty concentrating
- Language acquisition difficulties
- Reduced short-term and long-term memory for abstract information
- Significant difficulty in solving equations
- Easily overwhelmed by sensations
- Anxiety
- Social avoidance
Potential for adaptation
- People with Fragile X Syndrome can still retain important practical information
- They can effectively use the language(s) they have learned
- They have good visual memory
- They are able to concentrate on tasks using an electronic device.
How do you become a person with Fragile X syndrome?
Fragile X syndrome is hereditary. This means it is passed down from parent to child. The syndrome is linked to the X sex chromosome. People born female generally have two X chromosomes (XX). Those born male usually have one X and one Y chromosome (XY). Because everyone has an X chromosome, both females and males can have the syndrome. However, the symptoms will be different.
To find out moreWHAT'S DIFFERENT ABOUT THE X CHROMOSOME?
Chromosomes act like large libraries within our cells. They contain a large number of genes. Genes function like recipe books, containing the instructions needed to create the proteins that make up our bodies. These recipes are written in a special alphabet called DNA, which uses only four letters: A, T, C, and G.
Fragile X syndrome occurs when an error occurs in the FMR1 gene. The FMR1 gene contains a particularly complicated recipe for cells to read. Although each person is different, and therefore the recipes written in their genes vary, the recipe for the FMR1 gene always begins in the same way: the letters CGG repeated between 3 and 54 times. The FMR1 gene is a difficult recipe for cells to read because of the repetitions at the beginning, which make it harder for the cells to read the recipe as a whole.
In the case of Fragile X syndrome, it's as if there's been a "misprint" of the FMR1 recipe. The letters CGG are repeated over 200 times! The cells can no longer understand the recipe. They still produce the protein, but without correctly following all the instructions.
In summary, Fragile X syndrome occurs when the FMR1 recipe on the X chromosome becomes unreadable for our body's cells.
Fun fact
The syndrome is called Fragile X because the X chromosome appears fragile and seems ready to break where the FMR1 gene is located.

Fragile X syndrome in people born male (XY)
People born male with Fragile X syndrome tend to have more symptoms and more needs than those born female. Chromosomes contain the genes that are our body’s recipe books. People born male have only one X chromosome, so they have only one copy of each gene and recipe present on that chromosome. If a recipe is missing or badly written, the body can’t re-invent it and will have to make do without it. For this reason, people born male with Fragile X syndrome are more likely to experience significant intellectual development challenges, a distinctive facial appearance with elongated features and protruding ears, and generally more severe symptoms than those born female with the same syndrome. Furthermore, people born male with Fragile X often require significant support.
Fragile X syndrome in people born female (XX)
People born female with Fragile X syndrome have highly varied profiles. Generally, they have fewer symptoms than those born male because they have two copies of the X chromosome, and therefore two copies of each recipe. Cells can thus “compare recipes.” However, the bodies of people born with two X chromosomes (XX) will deactivate one copy of the X chromosome before birth. This mechanism is essential because the X chromosome contains the recipes for essential proteins that must be produced in a precise quantity. If the body kept two copies active, the cells would produce twice as many proteins!

When the X chromosome is deactivated
In some cases, the body deactivates the fragile X chromosome. These people will have almost no symptoms of the syndrome. The cells never consult the recipe containing the error after birth.
When only the X chromosome is active
Sometimes, the body keeps only the fragile X chromosome active. These people will experience more pronounced symptoms because the recipes contained in this chromosome will be the first consulted by the cells after birth. As a result, the symptoms of Fragile X syndrome will be more severe for these individuals.
Mosaic presentation
Sometimes, the body allows the cells to choose. Each cell then selects its preferred X chromosome. This is called a mosaic presentation. In these cases, symptoms vary greatly from one person to the next. This depends on the percentage of cells that have chosen the fragile X. Generally speaking, people born female with a mosaic presentation experience symptoms of anxiety. They often feel a constant need to compensate and pretend to be like everyone else, while sensing that something in their body works differently.
For find out more
Some people think that the Fragile X gene, FMR1, is dominant, i.e. it's a gene that expresses itself by default. For example, the brown-eye gene is dominant; it's the gene that expresses itself all the time if it's there, and suppresses the others. Blue-eyed people don't have the gene for brown eyes. However, the FMR1 gene is not dominant. The FMR1 gene has the same strength as other genes.
Are Fragile X syndrome and autism the same thing?
No, Fragile X syndrome and autism are not the same thing. Some traits are common to both conditions, such as being easily overwhelmed sensorially or fearing social activities. However, some traits are unique to Fragile X syndrome, such as distinct facial features or significant difficulty in solving equations. Conversely, some traits are unique to autism, such as communication difficulties that persist even when the person has a good command of the language. As mentioned at the beginning of the text, autistic people can also have Fragile X syndrome, and conversely, people with Fragile X syndrome can also be autistic.
“But I read a study that said they had found a cure for autism by studying Fragile X syndrome”
In November 2022, a group of American researchers published a study on autism, claiming to use the animal model of autism to better understand differences in the nervous system. To do this, they transmitted the FMR1 gene with a misprint to mice. As we saw earlier in this text, a misprint in the FMR1 gene is what causes Fragile X syndrome. They therefore bred mice exhibiting the animal version of Fragile X syndrome to study autism.
If this seems illogical, that’s because it is.
Researchers say that Fragile X syndrome is the leading genetic cause of autism since 25% of people with Fragile X are also autistic. However, many people with neurodivergence, such as Fragile X syndrome, autism, ADHD, or dyslexia, have associated conditions. For example, 30% of people with autism also have ADHD. But we can’t study autism to find drugs to help people with ADHD!
Nonetheless, this study provides some interesting insights into Fragile X syndrome in mice and perhaps in humans. Mice with Fragile X syndrome are hyposensitive, even though they are more easily overwhelmed sensorially. The reasons behind this contradiction need further investigation, if future research confirms this finding.
For further information
References
Ibarrondo. F., Camus. G. X chromosome inactivation in Mammalian females., Planet vie., 2012. (accessed 26-03-23)