Mother and child

Single-gene screeing

Dedicated genetic testing
for fragile X syndrome

In addition to a comprehensive screening for more than 500 genetic disorders (Inheritest), we also offer screening for specific disorders, such as fragile X syndrome, the most common inherited form of intellectual disability, and a common known cause of autism.1

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Fragile X syndrome

Fragile X syndrome is found among a variety of ethnic groups,2 and can occur in families with no history of inherited intellectual disability. Approximately one in 260 women3 and one in 800 males4 in the general population is a fragile X carrier. Since typically only a mother needs to be a carrier to pass on this disorder, the couple’s risk is higher than for cystic fibrosis. 

Why focus on fragile X screening?

Fragile X is the most common cause of inherited intellectual disability, which affects approximately 1 in 4,000 males and 1 in 8,000 females.1 Carrier screening for Fragile X will detect approximately 99% of individuals who are carriers of a mutation in the Fragile X gene and at risk of having a child with Fragile X syndrome.2 

Approximately 1 in 260 women3 and 1 in 800 males4 in the general population is a carrier of fragile X syndrome. Fragile X syndrome occurs when a woman who carries a fragile X mutation, passes this mutation on to her child. Fragile X syndrome can be seen in families with a history of intellectual disability or in families without any such history.

Individuals are considered to have an increased risk to be fragile X carriers if they have:

  • Family history of fragile X syndrome or fragile X related disorders
  • Family history of unexplained intellectual disabilities, developmental delay, or autism
  • Unexplained infertility problems, ovarian insufficiency or failure, elevated FSH levels, early menopause
  • Unexplained problems with balance or tremor

Choice in testing for fragile X syndrome

At Labcorp, our focus is offering the right test at the right time to the right patient, which is why we offer two types of testing for fragile X.

Carrier screening: 

  • Fragile X Carrier Screen is commonly used for individuals when there is no family history suggestive of the syndrome
  • For individuals who may have a family history of fragile X syndrome, fragile X-related disorders (primary ovarian insufficiency, or late-onset ataxia), or unexplained intellectual disabilities, developmental delay, or autism

Diagnostic testing (both prenatal and pediatric): 

  • Individuals at higher risk, including those that may be symptomatic or have a family history suggestive of fragile X syndrome
  • Female carriers of fragile X syndrome who are currently pregnant 
  • Women with primary ovarian insufficiency or failure, premature menopause, or infertility associated with elevated FSH levels before the age of 40 with no known cause 
  • Individuals (usually, infants or children) with unexplained intellectual disabilities, developmental delay, or autism

Additional Resources


  1. Sherman, S, et al. Fragile X syndrome: Diagnostic and carrier testing. ACMG Practice Guideline Genet Med 2005; 7(8):584–587.
  2. Maddalena, A, et al. Technical Standards and Guideline for Fragile X: The First of a Series of Disease-Specific Supplements to the Standards and Guidelines for Clinical Genetics Laboratories of the American College of Medical Genetics. Genet Med 2001; 3(3):200–205.
  3. Carrier Screening for Fragile X syndrome. ACOG Committee Opinion, Number 469. October 2010.
  4. Dombrowski, C., et al. Premutation and intermediate-size FMR1 alleles in 10,572 males from the general population: loss of an AGG interruption is a late event in the generation of Fragile X syndrome alleles. Hum Mol Genet 2002; 11(4):371–378.