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Alpha-thalassemia x-linked intellectual disability syndrome

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My son was diagnosed with alpha-thalassemia x-linked intellectual disability syndrome. The questions I have relate to other members of the family. I have a sister who has children. I understand that if my sister has the mutation, there is a chance that she passed it to her daughter, who would then be a carrier. But the literature I have read isn't completely clear regarding boys.  If my sister carries the mutation, could she have passed it to her son and could her son be an unaffected carrier of the mutation?

The following information may help to address your question:


How is alpha-thalassemia x-linked intellectual disability syndrome inherited?

Alpha-thalassemia x-linked intellectual disability (ATRX) syndrome is caused by a mutation in the ATRX gene and is inherited in an x-linked way.  The chance that a relative may have ATRX syndrome depends on whether the mutation in the first affected family member was inherited from his mother or happened by chance (a de novo mutation).  If the mutation happened by chance, there is very little risk that other relatives could be affected by this condition.  If the mutation was inherited from his mother, each of his mother's sisters has a 50% of being a carrier of ATRX syndrome.  If a woman is a carrier of an ATRX mutation, she has a 25% chance of having a son with the mutation who is affected with ATRX syndrome; a 25% chance of having a son who does not have the mutation and does not have ATRX syndrome; a 25% chance of having a daughter with the mutation who is a carrier of ATRX syndrome; and a 25% chance of having a daughter who does not have the mutation and is not a carrier.[1]
Last updated: 10/3/2012

Can a boy be an unaffected carrier of alpha-thalassemia x-linked intellectual disability (ATRX) syndrome?

No.  All boys who have a mutation in the ATRX gene have alpha-thalassemia x-linked intellectual disability syndrome.  Boys who do not have ATRX syndrome cannot pass this condition to their children.[1]
Last updated: 10/3/2012

We hope this information is helpful. We strongly recommend you discuss this information with your doctor. If you still have questions, please contact us.

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GARD Information Specialist

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  1. Stevenson RE. Alpha-thalassemia x-linked intellectual disability syndrome. GeneReviews. June 2010; http://www.ncbi.nlm.nih.gov/books/NBK1449/. Accessed 9/28/2012.