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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®

PAR gene family

Reviewed January 2012

What are the PAR genes?

Genes in the pseudoautosomal (PAR) gene family are located near the ends of the X and Y chromosomes in areas known as the pseudoautosomal regions. The X and Y chromosomes are the human sex chromosomes. Females have two X chromosomes in each cell, while males have one X chromosome and one Y chromosome in each cell. Although many genes are unique to either the X or Y chromosome, genes in the pseudoautosomal regions are present on both sex chromosomes. Males and females have two functional copies of most pseudoautosomal genes in each cell.

The pseudoautosomal regions on the X and Y chromosomes are known as PAR1 and PAR2. PAR1 is located at the end of the short (p) arm of the chromosomes and is about 2.7 million DNA building blocks (2.7 megabases) long. It contains at least 24 known genes. PAR2 is located at the end of the long (q) arm of the X and Y chromosomes and is about 330,000 DNA building blocks (0.33 megabases) long. It contains at least five known genes.

In males, the pseudoautosomal regions are needed for the X and Y chromosomes to line up correctly during cell division. X-Y pairing in PAR1 appears to be critical for the normal formation of sperm (spermatogenesis), and studies suggest that a loss of PAR1 is associated with an inability to father a child (infertility). The shorter PAR2 does not appear to be necessary for normal fertility.

Although many of the genes in PAR1 and PAR2 play important roles in normal development, only one pseudoautosomal gene, the SHOX gene in PAR1, has been definitively associated with human disease. Changes involving this gene are responsible for two related skeletal disorders, Léri-Weill dyschondrosteosis and Langer mesomelic dysplasia. One copy of the SHOX gene is also missing in females with Turner syndrome, causing them to have short stature and skeletal abnormalities. Additionally, variations in the SHOX gene have been associated with short stature in people without other features of a genetic syndrome (idiopathic short stature).

Which genes are included in the PAR gene family?

The HUGO Gene Nomenclature Committee (HGNC) provides an index of gene families ( and their member genes.

Genetics Home Reference summarizes the normal function and health implications of this member of the PAR gene family: SHOX.

What conditions are related to genes in the PAR gene family?

Genetics Home Reference includes these conditions related to genes in the PAR gene family:

  • Langer mesomelic dysplasia
  • Léri-Weill dyschondrosteosis
  • Turner syndrome

What glossary definitions help with understanding the PAR gene family?

cell ; cell division ; chromosome ; DNA ; dysplasia ; fertility ; gene ; homeobox ; idiopathic ; infertility ; sex chromosomes ; short stature ; sperm ; spermatogenesis ; stature ; syndrome

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


These sources were used to develop the Genetics Home Reference summary for the PAR gene family.

  • Flaquer A, Rappold GA, Wienker TF, Fischer C. The human pseudoautosomal regions: a review for genetic epidemiologists. Eur J Hum Genet. 2008 Jul;16(7):771-9. doi: 10.1038/ejhg.2008.63. Epub 2008 Apr 9. Review. (
  • Blaschke RJ, Rappold G. The pseudoautosomal regions, SHOX and disease. Curr Opin Genet Dev. 2006 Jun;16(3):233-9. Epub 2006 May 2. Review. (
  • Graves JA, Wakefield MJ, Toder R. The origin and evolution of the pseudoautosomal regions of human sex chromosomes. Hum Mol Genet. 1998 Dec;7(13):1991-6. Review. (
  • Flaquer A, Fischer C, Wienker TF. A new sex-specific genetic map of the human pseudoautosomal regions (PAR1 and PAR2). Hum Hered. 2009;68(3):192-200. doi: 10.1159/000224639. Epub 2009 Jun 11. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: January 2012
Published: November 23, 2015