triple X syndrome

Last reviewed 01/2018

This is an example of a sex chromosome abnormality.

This condition has a genotype 47, XXX.

The chromosomal abnormality 47,XXX occurs in one in a thousand female births; its incidence increases with increasing maternal age.

Non-disjunction at either female meiotic division or at the male second meiotic division is the cause of 47,XXX.

The clinical features associated with 47,XXX are extremely variable. Some possible features associated with 47,XXX are:

• often no distinguishing phenotype, especially in 1st year of life
• there may be slight neuromotor developmental delay, followed by slight delay in speech and language. Lack of co-ordination and poor academic performance with immature behaviour
• affected individuals tend to be tall
• normal sexual development
• there is an increased incidence of infertility in females affected by this condition
• considerable variability in syndrome makes counselling problematic: spectrum from learning disabilities to graduates