Children's Hospital Colorado

X&Y Chromosome Variations

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.

Get to know our pediatric experts.

Elizabeth Troy, MD

Elizabeth Troy, MD

Child Neurology

Jessica Outten, FNP

Jessica Outten, FNP

CPNP-AC, NP-C

Patient ratings and reviews are not available Why?

Lauren Haisley, PhD

Lauren Haisley, PhD

Clinical Neuropsychology

Patient ratings and reviews are not available Why?

Richard Boada, PhD

Richard Boada, PhD

Clinical Neuropsychology

Patient ratings and reviews are not available Why?