Genes in the male Y chromosome and in the genome of mitochondria may cause different types of male infertility, according to two studies in the upcoming issue of Nature Genetics. In one study, American scientists hone in on a region of the Y chromosome that is missing in men with low or no sperm production - the most common cause of infertility. In the other, European scientists find a variant of a mitochondrial gene associated with poor sperm quality.
The team led by David Page of the Whitehead Institute in Boston succeeded in characterizing in molecular detail the AZFc region of the Y chromosome, thought to contain genes important to sperm production and survival. After painstakingly piecing together the sequence of the region, Page and colleagues discovered that it is made up of several nearly identical DNA sequences that are repeated over and over in different combinations-the reason this region had been so difficult to study up to now. Among the repeated sequences, the researchers found 27 potential genes, all of which are expressed predominantly or exclusively in the testis. The authors suggest that the AZFc region becomes deleted in some men when repeated sequences on either side of it stick to one another - as identical DNA sequences often do -- and through a process known as homologous recombination literally come off the chromosome taking with them everything in between.
The second group, led by Howard T. Jacobs working at the University of Glasgow, Scotland, and the Tampere University Hospital, Finland, found that a gene in the DNA of mitochondria - the units within cells responsible for generating energy - was present in a different form in about 10% of men with infertility compared to healthy men. The different form of the gene was associated with types of infertility other than the complete absence of sperm (the type studied by Page's group). It is possible, the authors suggest, that the mitochondrial gene (called POLG) affects the amount of energy a sperm has to swim.
About one in ten couples in the US are unable to have children because of infertility. The identification of genes that affect the quantity and quality of sperm may provide ways to alleviate the problem, at least in men.
Whitehead Institute, Cambridge, USA
Tel: +1 617 258 5203
Howard T. Jacobs
Institute of Medical Technology
Tampere University Hospital, Finland
Tel: +358 3 215 7731
(C) Nature Genetics press release.
Message posted by: Trevor M. D'Souza