Spermatogenesis is a complex process regulated by a multitude of genes. The identification and characterization of male-germ-cell-specific genes is crucial to understanding the mechanisms through which the cells develop. The term “TEX gene” was coined by Wang et al. (Nat Genet. 2001; 27: 422–6) after they used cDNA suppression subtractive hybridization (SSH) to identify new transcripts that were present only in purified mouse spermatogonia. TEX (Testis expressed) orthologues have been found in other vertebrates (mammals, birds, and reptiles), invertebrates, and yeasts. To date, 69 TEX genes have been described in different species and different tissues. To evaluate the expression of each TEX/tex gene, we compiled data from 7 different RNA-Seq mRNA databases in humans, and 4 in the mouse according to the expression atlas database.Various studies have highlighted a role for many of these genes in spermatogenesis. Here, we review current knowledge on the TEX genes and their roles in spermatogenesis and fertilization in humans and, comparatively, in other species (notably the mouse). As expected, TEX genes appear to have a major role in reproduction in general and in spermatogenesis in humans but also in all mammals such as the mouse. Most of them are expressed specifically or predominantly in the testis. As most of the TEX genes are highly conserved in mammals, defects in the male (gene mutations in humans and gene-null mice) lead to infertility. In the future, cumulative data on the human TEX genes’ physiological functions and pathophysiological dysfunctions should become available and is likely to confirm the essential role of this family in the reproductive process. Thirteen TEX genes are now referenced in the OMIM database, and 3 have been linked to a specific phenotype. TEX11 (on Xq13.1) is currently the gene most frequently reported as being associated with azoospermia.

Tetrasomy 9p (ORPHA: 3310) (i(9p)) is a rare chromosomal imbalance. It is characterized by the presence of a supernumerary chromosome incorporating two copies of the short arm of chromosome 9 and is usually present in a mosaic state postnatally. Depending on the level of mosaicism, the phenotype ranges from mild developmental delay to multiple congenital anomalies with severe intellectual disability. Here, we report on a patient diagnosed with i(9p) mosaicism after the recurrent failure of in vitro fertilization. Although the patient's clinical phenotype was normal, the level of mosaicism varied greatly from one tissue to another. A sperm analysis evidenced subnormal spermatogenesis with chromosomally balanced spermatozoa and no risk of transmission to the offspring. Although individuals with i(9p) and no clinical manifestations have rarely been described, the prenatal diagnosis of this abnormality in the absence of ultrasound findings raises a number of questions.