What are X and Y chromosome aneuploidies?

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

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

Monosomy X (Turner syndrome)

Babies with monosomy X are biological females who have one X chromosome instead of two. Unfortunately, a high proportion of pregnancies with monosomy X will result in a miscarriage in the first or second trimester of pregnancy. Babies with monosomy X that make it to term may have heart defects, learning difficulties, and infertility. In most cases, babies with monosomy X will need extra medical care including hormone therapy at various stages of life

XXY Syndrome (Klinefelter Syndrome)

Babies with XXY syndrome have two X chromosomes and one Y chromosome (XXY). This condition can be associated with learning difficulties and behavioral problems. People with Klinefelter syndrome might be infertile. About 1 in 500 biological males will be born with Klinefelter syndrome.

Triple X syndrome

Babies with Triple X syndrome have three X chromosomes (XXX). Children with this condition could be taller than average and might experience learning difficulties or behavioral problems. Approximately 1 in 800 biological females will be born with three X chromosomes.

XYY Syndrome (Jacob's Syndrome)

Babies with XYY syndrome have one X chromosome and two Y chromosomes (XYY). Most babies with XYY syndrome do not have any birth defects. Children with XYY could be taller than average and have an increased chance for learning, speech, and behavioral problems. Approximately 1 in 1,000 biological males will be born with one X chromosome and two Y chromosomes.

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

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

For reasons we don't completely understand, children with X and Y chromosome variations can also have developmental delays, learning disabilities and social-emotional difficulties. Babies diagnosed prenatally or during infancy with an X and Y chromosome aneuploidy should be monitored closely during early developmental years (birth to 5), including standardised developmental assessments to determine if early interventions are needed. Children with an X and 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 and Y chromosome aneuploidies in males include:

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

X chromosome aneuploidies 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 and Y chromosome aneuploidies. 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.

EarlyLife

What are X and Y chromosome aneuploidies?