ANIMAL MODELS THAT MIMIC HUMAN MALE REPRODUCTIVE DEFECTS

Androgen receptor gene polyglutamine length is associated with testicular histology in infertile patients

PURPOSE

Androgens and a functioning androgen receptor are required for normal spermatogenesis. The androgen receptor gene (AR) has a repetitive DNA sequence in exon 1 that encodes a polyglutamine tract. Within the normal polymorphic range this (CAG)(n) tract length is inversely related to the transcriptional activity of the androgen receptor. In a prospective analysis we determined the association of AR (CAG)(n) tract length with testicular histology in infertile males.

MATERIALS AND METHODS

Blood DNA from 70 severely infertile patients without obstruction who were undergoing testicular biopsy was amplified by polymerase chain reaction targeting the AR (CAG)(n) tract. A total of 37, 15 and 18 men presented with the Sertoli-cell-only syndrome, maturation arrest and hypospermatogenesis, respectively. Blood DNA from 55 fertile men served as the control. Polymerase chain reaction amplified DNA was direct sequenced using a genetic analyzer.

RESULTS

Median CAG repeat length was 22 (range 17 to 33) in infertile patients and 21 (range 8 to 27) in controls (p = 0.009), including 22 (range 17 to 30) in patients with the Sertoli-cell-only syndrome, 22 (range 18 to 28) in those with maturation arrest and 23 (19 to 33) in those with hypospermatogenesis. Statistical significance was noted for the hypospermatogenesis versus control groups (p = 0.039) but not for the groups with the Sertoli-cell-only syndrome or maturation arrest versus the control group (p = 0.054 and 0.591, respectively).

CONCLUSIONS

Infertile males with testicular failure, particularly those with hypospermatogenesis, are more likely to have a longer androgen receptor polyglutamine tract than controls. Polymorphisms of the AR (CAG)(n) tract may contribute to spermatogenesis efficiency through a subtle modulatory effect on androgen receptor function.

The role of human and mouse Y chromosome genes in male infertility

It was suggested by Ronald Fisher in 1931 that genes involved in benefit to the male (including spermatogenesis genes) would accumulate on the Y chromosome. The analysis of mouse Y chromosome deletions and the discovery of microdeletions of the human Y chromosome associated with diverse defective spermatogenic phenotypes has revealed the presence of intervals containing one or more genes controlling male germ cell differentiation. These intervals have been mapped, cloned and examined in detail for functional genes. This review discusses the genes mapping to critical spermatogenesis intervals and the evidence indicating which are the most likely candidates underlying Y-linked male infertility.

Lessons from knockout and transgenic mice for infertility in men

This review concentrates on the clear cases where knocking out a gene in mice has caused male infertility and thus comes near to proving that the gene plays a role in the development of sperm. Knockout mice have been created with primary defects at every stage of spermatogenesis thus creating a framework for decoding the genetic hierarchy that causes male germ cell differentiation. As well as defining essential genes in vivo experiments have defined promoter and untranslated sequences responsible for the expression of proteins at all the spermatogenic stages. In conclusion knockout mice remain the ultimate test of spermatogenic hypotheses as well as providing detailed information about this complex process.

The genetic basis of infertility in men

Subfertility in men is a heterogeneous syndrome, its pathophysiology remaining unknown in the majority of affected men. A large number of genes and loci are associated with sterility in experimental animals, but the human homologues of most of these genes have not been characterized. A British study suggested that, in a large proportion of men with idiopathic infertility, the disorder is inherited as an autosomal recessive trait; this provocative hypothesis needs confirmation. Because normal germ cell development requires the temporally and spatially co-ordinated expression of a number of gene products at the hypothalamic, pituitary and testicular levels, it is safe to predict that a large number of autosomal, as well as X- and Y-linked, genes will probably be implicated in different subsets of male subfertility.

The genetic basis of male infertility

Defective spermatogenesis can be the end result of a multitude of causes, such as systemic disease, malnutrition, endocrinologic disorder, genetic defects, anatomic obstruction of the passage of spermatozoa, infections, and environmental toxins. A genetic basis of infertility is thought to exist in a majority of infertile men currently classified as having idiopathic infertility. Despite advances in molecular technology, the pathophysiology of spermatogenic failure in a majority of infertile men remains unknown. Although a large number of genes and loci in experimental animals are associated with sterility, the human homologues of most of these genes have not been cloned yet. Infertility is a heterogeneous syndrome in men; therefore, it is likely that a multitude of genes and loci will be implicated in different infertility subsets.