Rare diseases - Fragile X syndrome

Fragile X syndrome is associated with autism, seizures and learning difficulties, writes Dr Harry Brown

 What is it?

  • Fragile X syndrome is the commonest cause of an inherited learning disability. It is mediated through a genetic abnormality of the X chromosome, which appears ‘fragile’, hence the name. The abnormal gene is FMR1.
  • The full disease process resulting from the genetic abnormality has not completely been elucidated.

Who is at risk?

  • Males are twice as likely as females to have this condition, which affects approximately one in 4,000 of the male population; it is less prevalent in Asian people.
  • Fragile X syndrome is associated with autism and seizures, and its prevalence in children with learning difficulties may be around 1-2%.
  • FMR1 abnormalities are also associated with the fragile X ataxia syndrome, which causes cerebellar ataxia and tremor in those aged over 50.
  • Some female carriers are at risk of premature failure of their ovaries which can result in premature menopause, before 40 years of age.

Signs and symptoms

  • People affected by fragile X syndrome can possess a wide spectrum of abnormalities. Features may start to present in infancy. Developmental delay and learning difficulties can be manifestations of this disorder.
  • Depending on how significant the presenting symptoms and signs are, the diagnosis may not be made until school age or beyond. Heterozygous females may show no symptoms at all. The more genetic abnormalities present, the greater the likelihood of developing symptoms.
  • Behavioural abnormalities include impulsivity, hostility and minimal eye contact. Some affected males may have autism. Physical features include prominent jaw and forehead, large, prominent ears, and men who are past puberty may have large testicles.
  • Other features include mobile joints, squint and mitral valve prolapse. Some affected individuals have no physical signs; some fully affected females may have less obvious physical signs.
  • Always ask about a history of special needs education and a family history of intellectual problems and in women, premature menopause.

What is the treatment?

  • Early intervention, which means early diagnosis, can help. The diagnosis can be made on DNA analysis by looking at the abnormal gene on the X chromosome. Further carrier testing in the immediate family may be necessary and this should be accompanied by appropriate counselling.
  • There is no cure; treatment is mainly supportive, treating symptoms. It is a condition that affects a person throughout their life. Information provision is important and this takes time. Recognised support groups should be suggested to the affected family. Also consider therapists such as occupational and speech and language therapists.

 

Dr Brown is a GP in Leeds

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