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Fragile X syndrome

Inheritance patterns and prenatal diagnosis

Inheritance patterns
A carrier woman has a fifty per cent chance of passing on the fragile X chromosome to her children. Of these, males are likely to be affected by the syndrome, whilst daughters have a 1 in 3 chance of being clinically affected.

Men can also be unaffected carriers of the fragile X chromosome. In such cases the genetic change is passed to all daughters, but to none of the sons. These daughters will themselves be unaffected but at risk of having affected children. Any sons of carrier males will be completely unaffected as they do not receive their X chromosome from their father.

Prenatal diagnosis
Prenatal diagnosis is possible by chorionic villus sampling or fetal blood sampling. This is likely to give a definitive answer for affected males but cannot always distinguish affected from unaffected carrier females.

View How is it diagnosed? How is it diagnosed?  |  Is there support? View Is there support?

Medical text and Psychological and behavioural characteristics text written June 1997 by Dr A Barnicoat, Consultant in Clinical Genetics, Institute of Child Health, London, UK and Professor J Turk. Last updated December 2005 by Professor J Turk, Professor of Developmental Psychiatry and Consultant Child & Adolescent Psychiatrist, Department of Clinical Developmental Sciences, St. George's Hospital Medical School, London, UK.

 

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