X chromosomal mutations and spermatogenic failure.

The X and Y chromosomes, the sex chromosomes, are important key players in germ cell development. Both chromosomes contain genes that are uniquely expressed in male spermatogenesis. Furthermore, these chromosomes are special because men only have a single copy of them. These features make the sex chromosomes interesting for studying in view of spermatogenesis defects. The role of the Y chromosome, together with the presence of Yq microdeletions, in male infertility is well established. Less well-understood are the X-linked genes, their expression patterns and potential impact on male infertility. This review provides an overview of the current knowledge on potential spermatogenesis genes that are located on the mouse and human X chromosomes. A summary is given on knock-out mice models in which X-linked genes have been shown to alter spermatogenesis, and on genes that have been studied in humans. Finally, new research areas like miRNA analysis, Genome Wide Association Studies (GWAS) and array comparative genomic hybridisation (CGH) studies are discussed. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.