Fragile X Syndrome Testing

Fragile X syndrome (FXS) testing detects more than 99% of individuals (both males and females) with FXS, as well as carriers of the condition.

Testing should be considered in any individual with intellectual disability, developmental delay, autism spectrum disorder, or a family history of intellectual disability

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Fragile X syndrome is a genetic disorder affecting approximately 1 in 3,500 males and 1 in 7,000 females. It is the most common cause of inherited intellectual disability and developmental delay in males. Typically, males with fragile X syndrome are more severely affected than females and present with a range of neurodevelopmental difficulties including learning disabilities, cognitive impairment, and autism spectrum disorder (ASD).
•    Delayed developmental milestones and speech
•    Behavioral disorders, such as ASD, ADD, anxiety, aggression, and depression
•    Intellectual disability or learning problems (~100% of males, ~60% of females)
•    Medical features including seizures, strabismus, scoliosis, and heart murmurs
•    Physical characteristics, which are variable and may become more apparent over time, such as a long face, prominent forehead, large ears, and macro­‐orchidism
Fragile X syndrome is caused by changes in the FMR1 gene, which is located on the X chromosome. The FMR1 gene contains a CGG trinucleotide repeat in the promoter region before the coding sequence of the gene. Normally, this DNA segment is repeated 5-­40 times; however, in most individuals with fragile X syndrome, the CGG segment is repeated more than 200 times. Repeats of this size result in the methylation of the FMR1 gene, which silences the gene and prevents any protein from being produced.

The FMR1 gene not only causes fragile X syndrome but a spectrum of conditions called FMR1-related disorders depending on the CGG repeat size and gender.
Because the FMR1 gene is located on the X chromosome, fragile X syndrome is transmitted as an X-­linked disorder. If a female is known to be a carrier of fragile X syndrome, she has a 50% chance passing on the mutation to her children. Males with fragile X syndrome cannot pass on the condition to their sons; however, all their daughters would be carriers. Repeats between 55 and 200 (called premutations) are unstable and can increase in size as they are passed from parent to child. Therefore, premutation carriers (particularly females) are at risk for having children with fragile X syndrome.

We estimate the turnaround time to be about 3 to 4 weeks or results will be reported with FirstStepDx PLUS Chromosomal Microarray when ordered together.