1. Care & Services
  2. Prenatal Diagnosis
  3. Carrier Testing
  4. Fragile X

Fragile X

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. Approximately 1 in 260 women in the general population are carriers and women with unexplained infertility, premature ovarian failure or a family history of autism, developmental delay or unexplained intellectual disabilities may be at even higher risk.2

Fragile X syndrome has been found in all major ethnic groups and races. The phenotypic features of fragile X can include mental retardation, autism, elongated face, prominent ears or behavioral problems and often are not apparent until later in childhood, making it difficult to diagnose during the newborn period. The mean age of diagnosis is age 3 years.3

At San Diego Perinatal Center, we are currently recommending offering Fragile X carrier screening to all pregnant patients or women contemplating pregnancy regardless of their history because selective career screening will miss 50% of at risk families. Carrier screening and counseling ideally should be performed before pregnancy because this enables couples to learn about their reproductive risk and consider the most complete range of reproductive options. 

Carrier screening allows patients to make educated reproductive decisions and it gives them information about their personal health. Accurate prenatal fetal diagnosis is available and the choice can be offered whether to continue pregnancy. Prenatal diagnosis can lead to earlier postnatal intervention. Identification of carriers at risk for premature ovarian failure may allow for earlier and more effective reproductive interventions in those desiring pregnancy. Finally, screening all women prenatally, regardless of family history or specific risk factors, is cost effective when considering the burden of raising a child with fragile X syndrome.4


  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. https://www.acog.org/Clinical-Guidance-and-Publications/Committee-Opinions/Committee-on-Genetics/Carrier-Screening-for-Genetic-Conditions?IsMobileSet=false
  4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3651542/