There are so many different personalities, intellects, talents, and passions in this world. Unique people make this world interesting and provide improvement and progression in life. Genetics play a key role in people being different from each other, even within a single family. While changes in our genetics can bring strengths in someone, they can also bring disease, intellectual disability, or other health challenges. For example, in the case of autism spectrum disorder (ASD) there are over 1,000 genetic components that play a role in the condition. We know that autism spectrum disorder is typically a combination of genetics and environment. However, the most common inherited form of ASD in boys is Fragile X syndrome and does not typically only involve autism.
What is Fragile X Syndrome?
Fragile X syndrome is caused by a change in a gene called FMR1. The change in the FMR1 gene that causes this syndrome is called a CGG trinucleotide repeat expansion. In the beginning of the coding of the FMR1 gene, there is an extra code with 3 letters (CGG) that is repeated over and over, which causes the gene to not work properly. People with the genetic condition that results in Fragile X have over 200 of these CGG repeats in the beginning of their FMR1 gene. This repeat in the FMR1 gene is passed on from generation to generation in an X-linked pattern, meaning it is carried on the X chromosome. Women have two X chromosomes and men have one X chromosome and one Y chromosome. Because women have two X chromosomes, they are considered carriers, with one X chromosome having the repeats on the nonfunctioning FMR1 gene and the other X chromosome having a functioning FMR1 gene. However, because men only have one X chromosome, if they inherit the repeats on their FMR1 gene on their X chromosome, they will have Fragile X syndrome.
It is important to note that the repeats don’t jump to over 200 on the FMR1 gene by only being passed on once. An FMR1 gene that has a normal number of repeats typically has between 5 and 44 CGG repeats. A “gray zone”, where the FMR1 gene has the potential to become unstable and gain more repeats is 45-54 CGG repeats. Someone who is considered a “premutation carrier”, meaning there is a higher risk of the repeats getting bigger and turning into this syndrome is 55-200 CGG repeats. Female carriers of a “premutation” for Fragile X syndrome are at increased risk for primary ovarian insufficiency, meaning they can struggle with infertility and menopausal-like symptoms at an earlier age. Both female and male “premutation” carriers for Fragile X syndrome are also at risk of a tremor/ataxia syndrome, which is where someone can develop tremors, parkinsonian symptoms, dementia, or cognitive impairment starting around 60 years of age.
When males inherit a full mutation of over 200 CGG repeats, they are diagnosed with Fragile X syndrome. Someone with Fragile X syndrome can have ADD, ASD and autistic behaviors, social anxiety, intellectual disability, physical features such as large ears, long face, soft skin, and large testicles, and an overall friendly disposition. Females can inherit a full mutation and have some symptoms of Fragile X syndrome, but because of their second X chromosome their symptoms aren’t as severe. Females can have mild intellectual disability and ASD but can also never show symptoms.
Unfortunately, there is no cure for Fragile X syndrome. There are many clinics throughout the United States and around the world that treat this condition. These clinics can guide parents in how to best help their children and support them in growth and development. There are a variety of therapies and special education services that can help someone suffering from this condition thrive and improve their quality of life.
Worried About Fragile X Syndrome or Other Genetic Conditions? We Can Help
For individuals who are suspected to have Fragile X syndrome, there are genetics tests that only involve a blood draw that can be performed to confirm the diagnosis . Likewise, there are genetics tests that can be done to see if someone is a carrier for this and other genetic conditions, and which category of repeats they fall into. If a couple finds out during pregnancy that there is a risk of the pregnancy having this syndrome, diagnostic tests such as an amniocentesis are available to test the pregnancy.
If you have a family history of ASD or Fragile X syndrome, or would simply like to know if you are at risk to have a child with Fragile X, please contact AT-GC to schedule an appointment with a genetic counselor to assess your risk.