Data & Statistics
Fragile X syndrome (FXS) is the most common known cause of inherited intellectual disability.1 FXS affects both males and females. Females often have milder symptoms than males.2 The exact number of people who have FXS is unknown, but it has been estimated that about 1.4 per 10,000 males and 0.9 per 10,000 females have FXS.3
- Among people affected with FXS, intelligence quotient (IQ) scores decline noticeably with age: adolescents and adults consistently score lower on IQ tests than young children.4
- Young children with FXS often take longer than their peers without FXS to reach early language milestones and to develop nonverbal communication (communication without words, typically through gestures, facial expressions, and body language).4
- While the average IQ score of the general population is 100, boys with FXS have an average IQ score under 55.4
- The average age of FXS diagnosis for boys is 35 to 37 months. Girls are diagnosed at an average age of 42 months.5[Read article]
- Parents are usually the first to notice symptoms of FXS at about 12 months of age for boys and 16 months of age for girls.5[Read article]
- Parents reported repeat healthcare visits before their healthcare provider diagnosed developmental delay at an average age of 20 months for boys and 26 months for girls.
- Health professionals typically diagnosed FXS about 16 months after confirming a developmental delay.
- About 4 in 10 families reported that they visited a health professional at least 10 times before their child was diagnosed with FXS.6[Read article]
Co-Occurring Conditions and Characteristics
- A national parent survey found that most individuals with FXS had been diagnosed or treated for other conditions that occur together (co-occurring) with FXS.7[Read scientific summary]
|Fragile X Co-Occurring Conditions (As reported by parents)||Males||Females|
|Developmental Delay or Intellectual Disability||96%||64%|
- A study of 557 people with FXS between 3 and 21 years of age found that8[Read article]
- Just over 4 in 10 individuals had both FXS and autism spectrum disorder (ASD).
- Individuals with both FXS and ASD were about 3 times more likely to experience seizures than individuals with FXS alone.
- Approximately 4 in 10 individuals with both FXS and ASD had sleep problems that required treatment, compared to 3 in 10 individuals with FXS alone.
- There was a higher proportion of attention problems, hyperactivity, hypersensitivity/over reactivity, perseverative/obsessive compulsive behavior, and irritability/aggressive behavior/agitation/ self-injury among those with both FXS and ASD as compared to those with FXS alone.
- Aggressive/disruptive behavior was the only behavior treated with medicine more often in individuals with both FXS and ASD compared to those with just FXS. About 4 in 10 individuals with both FXS and ASD were treated with medicine for aggressive/disruptive behavior compared with less than 2 in 10 individuals with FXS alone.
- Compared to children who only have ASD, children with both FXS and ASD may be less likely to receive Behavior Therapy.
- About 3 in 10 boys with FXS but only 2 in 10 typically-developing boys are obese.9 [Read scientific summary]
Adult Life of Men and Women with FXS
- Among adults with FXS, men are less likely than women to be able to read books with new words or ideas, speak using complex sentences, or speak at a typical speed.10[Read scientific summary]
|Abilities Among Adults with FXS||Men||Women|
|Read books with new words or ideas||19%||76%|
|Speak using complex sentences||62%||89%|
|Speak at a typical speed||62%||90%|
- A national family survey of adults with FXS showed that11[Read scientific summary]
- About 4 in 10 women with FXS achieved a high or very high level of independence in adult life compared to about 1 in 10 men.
- About 4 in 10 women with FXS lived independently, often with a spouse or romantic partner, compared to 1 in 10 men who lived independently, and rarely with a spouse or romantic partner.
- About 8 in 20 women with FXS required no assistance with activities of daily living compared to 1 in 20 men.
- The majority of women with FXS had at least a high school diploma; the majority of men did not have a high school diploma.
- Almost half of women with FXS had full-time jobs, compared to 2 in 10 men.
People with a fragile X premutation do not have fragile X syndrome but might have another fragile X-associated disorder. Some people with fragile X premutations have noticeable symptoms, and others do not.
- The exact number of people who have a fragile X premutation is unknown. Studies estimate that between 1 in 148 and 1 in 291 females and 1 in 290 and 1 in 855 males in the United States may have a fragile X premutation.12-17
- These numbers are important because both men and women are at risk for having symptoms related to fragile X-associated disorders.13[Read article]
- Women with a premutation reported their last menstrual cycle at an earlier age (on average, 48 years) than women without a premutation (on average, 51 years).
- Men and women with a premutation were more than four times as likely to report dizziness or fainting and more than twice as likely to report numbness compared to people without a premutation.
- People with a premutation are almost twice as likely to have a child with a disability as people without a premutation.13[Read article]
- A national parent survey found that males and females with fragile X premutation were more likely to have been diagnosed or treated for other conditions that occur together with FXS compared to people who did not have a premutation.7[Read scientific summary]
|Fragile X Premutation Co-Occurring Conditions (As reported by parents)||Males||Females|
|Developmental Delay or Intellectual Disability||32%||6%|
- With each additional condition occurring with FXS, there was greater financial burden for the family.
- About half of families reported that FXS caused a financial burden.
- In more than 6 in 10 families, parents changed work hours, stopped working, or turned down a job because of having a child with FXS.
- Families reported that therapies accounted for about one-third of their FXS-related out-of-pocket expenses. An additional third of out-of-pocket expenses went to medicines and other medical costs, including genetic testing and developmental evaluations.
Visit the Articles & Key Findings page to read recent articles on FXS written by CDC scientists or funded by CDC.
- Hersh JH, Saul RA, Committee on Genetics. Health supervision for children with fragile X syndrome. Pediatrics. 2011 May;127(5):994-1006.
- Keysor CS, Mazzocco MM. A developmental approach to understanding fragile X syndrome in females. Microscopy Research and Technique. 2002 May 1;57(3):179-186.
- Hunter J, Rivero-Arias O, Angelov A, Kim E, Fotheringham I, Leal J. Epidemiology of fragile X syndrome: a systematic review and meta-analysis. Am J Med Genet A. 2014 Jul 164A(7): 1648-58.
- Raspa M, Wheeler A, Riley C. Public health literature review of fragile X syndrome. Pediatrics. 2017 June 1;139(Supplement 3):s153-s171.
- Bailey DB Jr, Raspa M, Bishop E, Holiday D. No change in the age of diagnosis for fragile X syndrome: Findings from a national parent survey. Pediatrics. 2009 Aug;124(2):527-533.
- Bailey DB Jr, Skinner D, Sparkman KL. Discovering fragile X syndrome: Family experiences and perceptions. Pediatrics. 2003 Feb;111(2):407-416.
- Bailey DB Jr, Raspa M, Olmsted M, Holiday DB. Co-occurring conditions associated with FMR1 gene variations: Findings from a national parent survey. American Journal of Medical Genetics Part A. 2008 Aug 15;146A(16):2060-2069.
- Kaufmann WE, Kidd SA, Andrews HF, Budimirovic DB, Esler A, Haas-Givler B, Stackhouse T, Riley C, Peacock G, Sherman SL, Brown T, Berry-Kravis E. Autism spectrum disorder in fragile X syndrome: Co-occurring conditions and current treatment. Pediatrics. 2017 June 1;139(Supplement 3):s194-s206.
- Raspa M, Bailey DB Jr, Bishop E, Holiday D, Olmsted M. Obesity, food selectivity, and physical activity in individuals with fragile X syndrome. American Journal on Intellectual and Developmental Disabilities. 2010 Nov;115(6):482-495.
- Bailey DB Jr, Raspa M, Holiday D, Bishop E, Olmsted M. Functional skills of individuals with fragile X syndrome: A lifespan cross-sectional analysis. American Journal on Intellectual and Developmental Disabilities. 2009 Jul;114(4):289-303.
- Hartley SL, Seltzer MM, Raspa M, Olmstead M, Bishop E, Bailey DB Jr. Exploring the adult life of men and women with fragile X syndrome: Results from a national survey. American Journal on Intellectual and Developmental Disabilities. 2011 Jan;116(1):16-35.
- Tassone F, Iong KP, Tong TH, Lo J, Gane LW, Berry-Kravis E, Nguyen D, Mu LY, Laffin J, Bailey DB, Hagerman RJ. FMR1 CGG allele size and prevalence ascertained through newborn screening in the United States. Genome Medicine. 2012 Dec 21;4(12):100.
- Seltzer MM, Baker MW, Hong J, Maenner M, Greenberg J, Mandel D. Prevalence of CGG expansions of the FMR1 gene in a US population-based sample. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics. 2012 Jul;159(5):589-597.
- Maenner MJ, Baker MW, Broman KW, Tian J, Barnes JK, Atkins A, McPherson E, Hong J, Brilliant MH, Mailick MR. FMR1 CGG expansions: Prevalence and sex ratios. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics. 2013 Jul;162B(5):466-473.
- Rousseau F, Rouillard P, Morel ML, Khandjian EW, Morgan K. Prevalence of carriers of premutation-size alleles of the FMRI gene–and implications for the population genetics of the fragile X syndrome. American Journal of Human Genetics. 1995 Nov;57(5):1006-1018.
- Hantash FM, Goos DM, Crossley B, Anderson B, Zhang K, Sun W, Strom CM. FMR1 premutation carrier frequency in patients undergoing routine population-based carrier screening: Insights into the prevalence of fragile X syndrome, fragile X-associated tremor/ataxia syndrome, and fragile X-associated primary ovarian insufficiency in the United States. Genetics in Medicine. 2011 Jan;13(1):39-45.
- Hunter J, Rivero-Arias O, Angelov A, Kim E, Fotheringham I, Leal J. Epidemiology of fragile X syndrome: A systematic review and meta-analysis. American Journal of Medical Genetics Part A. 2014 Jul;164A(7):1648-1658.
- Ouyang L, Grosse S, Raspa M, Bailey DB Jr. Employment impact and financial burden for families of children with fragile X syndrome: Findings from the National Fragile X Survey. Journal of Intellectual Disability Research. 2010 Oct;54(10):918-928.
- Page last reviewed: May 7, 2018
- Page last updated: May 21, 2018
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