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Overview of Sex Chromosome Abnormalities

By

Nina N. Powell-Hamilton

, MD, Sidney Kimmel Medical College at Thomas Jefferson University

Reviewed/Revised Nov 2023
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Sex chromosome abnormalities may be caused by full or partial deletions or duplications of sex chromosomes.

Except for certain cells (for example, sperm and egg cells or red blood cells), every human cell contains 23 pairs of chromosomes, for a total of 46 chromosomes. There are 22 pairs of chromosomes that are not sex chromosomes (called nonsex chromosomes, numbered chromosomes, or autosomal chromosomes) and one pair of sex chromosomes.

The sex chromosomes Sex chromosomes Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body or the code for functional ribonucleic... read more Sex chromosomes determine whether a fetus becomes male or female. A pair of X and Y chromosomes (XY) results in a male, and a pair of X and X chromosomes (XX) results in a female.

Sex chromosome abnormalities occur when a person is missing a whole sex chromosome (called monosomy) or has an extra sex chromosome (called a duplication). Abnormalities can also occur when a person is missing part of a sex chromosome (called a deletion).

Sex chromosome abnormalities are common and cause syndromes that are associated with a range of physical and developmental problems. Many of these syndromes are not noticed while the mother is pregnant but may be discovered if prenatal testing Prenatal Testing for Genetic Disorders and Birth Defects Prenatal testing for genetic disorders and birth defects involves testing a pregnant woman or fetus before birth (prenatally) to determine whether the fetus has certain abnormalities, including... read more is done for other reasons, such as older age in the mother. The abnormalities are often hard to recognize at birth and may not be diagnosed until puberty.

Syndromes that are caused by a sex chromosome abnormality are less severe than those caused by a nonsex chromosome abnormality. For example, girls who have an extra sex chromosome (an extra X) often appear normal physically and mentally and are fertile. In contrast, children who have an extra nonsex chromosome typically have a severe disorder, such as trisomy 13 Trisomy 13 Trisomy 13 is a chromosomal disorder caused by an extra chromosome 13 that results in severe intellectual disability and physical abnormalities. Trisomy 13 is caused by an extra chromosome 13... read more , which results from a person having an extra chromosome 13.

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