A  A  A   Print
Trinucleotide Repeats: Fragile X SyndromeRepeticiones Trinucleótidas: el Síndrome X Frágil

Trinucleotide Repeats: Fragile X Syndrome

What are trinucleotide repeats?

DNA, the chemical that makes up our genes, contains a "code" of three-letter words known as "codons" or "trinucleotide repeats." Many genes normally contain a trinucleotide repeat which is present in several copies. But when the number of trinucleotide repeats increases to a larger than normal number of copies, the DNA is altered; therefore, the gene may not function properly, or may not work at all.

It is not well understood what causes a trinucleotide repeat to expand into more than the usual number of copies that should be in a gene. Sometimes, a person may have more than the usual number of copies, but not enough to alter the function of the gene. These individuals are referred to as "premutation carriers." When they pass on these extra copies to a child, however, those extra trinucleotide repeats cause the DNA to become unstable, and the area of DNA expands even more. The result is that the child has a gene that is not functioning properly (if at all), and the child is said to have the "full mutation." An example of a trinucleotide repeat disorder is Fragile X syndrome.

What is Fragile X syndrome?

Fragile X syndrome causes intellectual disability. This can range from mild to moderate to severe, in both males and females. However, males are typically more severely affected than females. Symptoms of Fragile X syndrome in childhood are not always specific. They overlap with other disorders, such as autism, Prader-Willi syndrome, and attention deficit-hyperactivity disorder (ADHD). Symptoms may include delays in development of speech, language, and motor skills. Autistic-like behavior, frequent tantrums, and hyperactivity are also commonly seen with Fragile X syndrome. Gaze aversion, or the inability to make and hold eye contact, is very common among males and females with Fragile X syndrome.

The gene that causes Fragile X syndrome, called FMR1, is located on the X chromosome. Females are usually not as severely affected as males. That is because females have a normal X chromosome, in addition to the X with the mutation. The FMR1 gene normally contains fewer than 44 trinucleotide repeats. Premutation carriers have about 55 to 200 trinucleotide repeats. People with Fragile X syndrome full mutation have over 200 repeats.

 
Today's Interactive Tools
Related Items

The third-party content provided in the Health Library of phoebeputney.com is for informational purposes only and is not designed to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your physician. If you or your child has or suspect you may have a health problem, please consult your primary care physician. If you or your child may have a medical emergency, call your doctor or 911 or other emergency health care provider immediately in the United States or the appropriate health agency of your country. For more information regarding site usage, please visit: Privacy Information, Terms of Use or Disclaimer.

Follow us online:

© 2014 Phoebe Putney Health System  |  417 Third Avenue, Albany, Georgia 31701  |  Telephone 877.312.1167

Phoebe Putney Health System is a network of hospitals, family medicine clinics, rehab facilities, auxiliary services, and medical education training facilities. Founded in 1911,
Phoebe Putney Memorial Hospital (the flagship hospital) is one of Georgia's largest comprehensive regional medical centers. From the beginning, Phoebe's mission and vision
has been to bring the finest medical talent and technology to the citizens of Southwest Georgia, and to serve all citizens of the community regardless of ability to pay.