Fragile X syndrome | Better Health Channel
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Summary

Fragile X syndrome is an inherited condition causing various degrees of intellectual disability. It affects males more than females and is the most common known cause of inherited intellectual disability. Some children with Fragile X syndrome will display behaviours similar to those of children with autism, including hand flapping and repeating of words and sentences. Males with Fragile X syndrome may have physical features such as large prominent ears, enlarged testes and very flexible joints. Genetic counselling can help people understand how Fragile X might affect their family.

Fragile X syndrome is a genetic disorder caused by an alteration in the X chromosome (that is, a change in the DNA structure). It results in a wide range of developmental, physical and behavioural problems, and is the most common known cause of inherited intellectual disability. Prevalence estimates for Fragile X syndrome vary – the best estimate is that about one in 4,000 males has this syndrome.

Fragile X syndrome varies in its presentation


The most significant effects of Fragile X syndrome are:
  • Developmental delay
  • Intellectual disability
  • Behavioural problems
  • Mimicking.
The degree of intellectual disability can vary from mild learning difficulties through to severe intellectual impairment. Behavioural problems are present in some Fragile X individuals. These effects tend to be more severe in males than in females.

Characteristics of Fragile X syndrome


Some children with Fragile X syndrome will display behaviours similar to those of children with autism, including:
  • Hand flapping
  • Repeating of words and sentences.
Fragile X males may have certain physical features, including:
  • Large, prominent ears
  • Enlarged testes
  • Flexible joints.
Not all of these characteristics are seen in every person with Fragile X syndrome.

Chromosomes explained


Chromosomes are located in the cells of the human body and contain all our genetic information. In every cell, there are 23 pairs of chromosomes, one pair of which determines the sex of a person. A male has an X and a Y, a female has two X chromosomes. A child will receive one of their sex chromosomes from the father’s sperm (X or Y) and one from the mother’s egg (X).

Fragile X syndrome is inherited


The Fragile X syndrome is inherited in a way known as ‘X-linked’. The altered gene is on the X chromosome.

On the X chromosome, there is a gene called FMR1, which produces a protein that helps the brain to function normally. If this gene is altered, it cannot produce its normal protein. Our genes often contain regions that are repeated. In the ‘normal’ form of the gene, there will be between five and 55 repeated copies of a small section of the gene. In a person with Fragile X syndrome, this copy number is increased to more than 200 repeats (called a ‘full mutation’). When there are more then 200 repeats, the gene is switched off, leading to the symptoms seen in Fragile X syndrome.

A repeat number of between 55 and 200 is classed as a ‘pre-mutation’. The number of repeats may increase when the mother passes on her X chromosome to her child. Therefore, an apparently unaffected woman – with fewer than 200 repeats – may have an affected son or daughter with greater than 200 repeats.

Other effects of Fragile X premutations


In the past it was thought that the only significance of a person having a Fragile X premutation was that women with permutations were at risk of having a child with Fragile X syndrome. Recently it has been discovered that Fragile X permutations can have additional health effects. Approximately 20 per cent of females with a Fragile X premutation experience premature menopause (menopause prior to age 40 years), and males (and some females) with permutations are at risk of a late onset neurological disorder called Fragile X Tremor Ataxia syndrome (FXTAS).

Counselling is available


The facts about Fragile X are complicated, and parents and family members are invited to ask their doctor to refer them to a genetics clinic. The genetics clinic can provide diagnostic and counselling services, including information about reproductive options. Clinics are held in Victoria in metropolitan Melbourne, Geelong, Ballarat, Bendigo, Albury/Wodonga, Mildura, Shepparton, Warragul, Warrnambool, Frankston and Sale/Traralgon. Contact Genetic Health Services Victoria for more information about Fragile X syndrome or to organise an appointment.

Where to get help

Things to remember

  • Fragile X is the most common cause of inherited intellectual disability.
  • Fragile X affects males more than females.
  • The children of unaffected carriers may be affected by Fragile X syndrome.
  • Genetic counselling is available and recommended.
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This page has been produced in consultation with and approved by:

Genetic Health Services Victoria Murdoch Childrens Research Institute

(Logo links to further information)
Genetic Health Services Victoria

Last reviewed: July 2011

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<a href="http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Fragile_X_syndrome?open">Fragile X syndrome - Better Health Channel</a><br/>
Fragile X syndrome is an inherited condition causing various degrees of intellectual disability. It affects males more than females and is the most common known cause of inherited intellectual disability. Some children with Fragile X syndrome will display behaviours similar to those of children with autism, including hand flapping and repeating of words and sentences. Males with Fragile X syndrome may have physical features such as large prominent ears, enlarged testes and very flexible joints. Genetic counselling can help people understand how Fragile X might affect their family.

Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your qualified health professional. Content has been prepared for Victorian residence and wider Australian audiences, and was accurate at the time of publication. Readers should note that over time currency and completeness of the information may change. All users are urged to always seek advice from a qualified health care professional for diagnosis and answers to their medical questions.

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