Alpha Thalassaemia X-intellectual disability syndrome

Also known as: Alpha Thalassaemia Mental Retardation syndrome; Mental Retardation on the X-chromosome


Alpha Thalassaemia X-intellectual disability (ATR-X) syndrome is a very rare genetic condition that affects boys only. It causes learning disability, a characteristic facial appearance and mild anaemia (low level of haemoglobin in red blood cells).

Over 300 families have been identified worldwide with the condition.


Last updated June 2017 by Richard Gibbons, Professor of Clinical Genetics, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, UK.

Although great care has been taken in the compilation and preparation of all entries to ensure accuracy, we cannot accept responsibility for any errors or omissions. Any medical information is provided is for education/information purposes and is not designed to replace medical advice by a qualified medical professional.

What are the symptoms?

Boys affected by ATR-X syndrome may experience the following:

  • learning disability and delayed development – boys show a varied range of learning difficulty/intellectual disability and delay in meeting developmental milestones
  • lack of language – this is common with some boys only learning to sign a few words
  • hypotonia (weak muscle tone) – which delays motor skills, such as sitting, standing and walking and can affect feeding as well
  • distinctive facial appearance – including widely spaced eyes, a small nose with upturned nostrils and low-set ears
  • alpha thalassaemia – most boys have mild signs of this. The condition reduces the production of haemoglobin which carries oxygen around the body. Sometimes red blood cells may be small in size (microcytic anaemia)
  • microcephaly (small head size)
  • short stature
  • skeletal abnormalities
  • gastrointestinal problems – gastroesophageal reflux (backflow of stomach acid into the food pipe) and constipation
  • genital abnormalities – affected males may have undescended testicles, hypospadias (opening of the urethra on the underside of the penis), or ambiguous genitals (those that do not look male or female).

What are the causes

ATR-X syndrome is caused by a mutation in the ATRX gene. Although the exact function of the ATRX gene is unknown, it is thought to be involved in regulating the expression of other genes in the body.

How is it diagnosed?

By using a specific stain, the red blood cells of someone affected by ATR-X syndrome have a golf ball-like appearance under the microscope which allows the diagnosis of ATR-X to be confirmed by a simple blood test in 85% of cases.

Testing the DNA to look for the change (mutation) in the ATRX gene can confirm the diagnosis.

How is it treated?

Boys affected by the condition require support in various areas to develop to their full potential. Infant stimulation, early intervention and special education are very important to encourage development. Alternative forms of communication, such as signing, PECS and Makaton may be used. Infantile hypotonia is common and is associated with difficulty sucking, so extra nutritional support may be needed (such as special teats and tube feeding into the stomach). Medications may be used to alleviate gastroesophageal reflux. Physical therapy may be needed to help movement and also relieve spasticity (tightness in muscle) if it occurs.

The anaemia associated with alpha thalassaemia is usually mild and very few cases need treatment. Undescended testes should be monitored with scanning, as the testicles may become cancerous if left inside the abdomen.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
This condition is transmitted in an X-linked recessive manner. Affected families should be referred to a genetics centre for information and support.

Prenatal diagnosis
This may be possible in some families where the mutation in the family has been identified.

Is there support?

ATR-X Support Group

Tel: 01606 44943

The group offers support for people affected by Alpha Thalassaemia and their families. It links families where possible, and welcome calls from anyone with an interest in this condition.

Group details last updated January 2016.

There is a very active international Facebook page for affected families. It’s a closed group but can be reached at:

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