Children's Hospital Colorado
Turner Syndrome Clinic

X&Y Chromosome Variations

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What are X&Y chromosome variations?

X&Y chromosome variations refer to conditions in which a child has an abnormal number of sex chromosomes, also known as X&Y chromosomes.

Other words used to describe X&Y chromosome variations are sex chromosome anomaly, sex chromosome abnormality and sex chromosome aneuploidy.

How do X&Y chromosome variations affect boys and girls?

Males usually have one X and one Y chromosome, and females usually have two X chromosomes. Occasionally, because of problems with the formation of a parent’s sperm or egg, a child can be born with extra or too few sex chromosomes.

For reasons we don't completely understand, children with X&Y chromosome variations can also have developmental delays, learning disabilities and social-emotional difficulties. Babies diagnosed prenatally or during infancy with an X&Y chromosome variation should be monitored closely during early developmental years (birth to 5), including standardized developmental assessments to determine if early interventions are needed. Children with an X&Y chromosome variation should have neuropsychological testing during early academic years to monitor for learning disabilities, attentional problems and social/emotional concerns. Boys with extra X chromosomes need to be seen by an endocrinologist during puberty to help monitor their testosterone levels. Girls who are missing an X chromosome (Turner syndrome) also need ongoing monitoring and treatment by endocrinology, cardiology and other specialties. 

X&Y chromosome variations in males include:

  • 47,XXY (Klinefelter syndrome)
  • 47,XYY
  • 48,XXYY
  • 48,XXXY
  • 49,XXXXY

X chromosome variations in females include:

  • 45,X (Turner syndrome)
  • 47,XXX (Trisomy X or Triple X)
  • 48,XXXX (Tetrasomy X)
  • 49,XXXXX (Pentasomy X)

What causes sex chromosome variations? 

Children are born with X&Y chromosome variations. These conditions are caused by a problem in the division of the X and Y chromosomes during the formation of a parent's egg or the sperm, which are then involved in conception. The exact cause is unknown, and these conditions are typically not inherited.

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Kelly Wolfe, PhD

Kelly Wolfe, PhD

Neuropsychology, Neuropsychology - Pediatric

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Michele Yang, MD

Michele Yang, MD

Neurology - Pediatric

Peter Baker, MD

Peter Baker, MD

Clinical Biochemical Genetics, Clinical Genetics and Genomics - General, Pediatrics

Eileen Yager, MD

Eileen Yager, MD


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