Reference Work Entry

Encyclopedia of Child Behavior and Development

pp 1584-1585

XXXY Syndrome

  • Adeline LowAffiliated withPsychology


Barr-Shaver-Carr syndrome; 48 XXXY syndrome


The XXXY syndrome is a sex chromosome that affects one in 17,000 boys. It can also be called 48, XXXY syndrome because such individual has 48 chromosomes instead of the normal 46, due to the extra two sex chromosomes. Most researchers believe that 48, XXXY syndrome is a variation of Klinefelter syndrome (XXY syndrome), with the 47, XXY syndrome’s dysmorphic features being mild, multiple and widespread in the 49, XXXXY syndrome and intermediate level of the spectrum in 48, XXXY. In Klinefelter cases, 80% of them are the karotype of 47, XXY, while the remaining 20% are the different variants, including mosaicism. Among all the variants, 48, XXXY is the commonest observed. With the addition of each X chromosome, there is a significant increase in somatic malformations and mental retardation.


The symptoms and effects of Klinefelter syndrome increase with each additional X chromosome present in the male ...

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