An international study has identified more than 50 genes on the X chromosome that may lead to poor sperm production and contribute to male infertility.

In a paper published in The American Journal of Human Genetics, the international team of researchers revealed how they sequenced the genes of infertile male patients, and compared them with sequences from non-infertile men to determine the differences.

While previous research has shown that the X chromosomes play a role in male fitness, their role in sperm formation has been largely ignored, and only three X chromosomes have been identified as being involved in problems with sperm production.

In this new study, the researchers took a closer look at the X chromosomes in male patients with two types of male infertility: azoospermia and cryptozoospermia. The first case includes patients who have problems with sperm motility, and the second includes patients who produce little or no sperm.

In the recent study, the researchers worked on sequencing the X chromosome from samples collected from 2,350 male patients, suffering from either azoospermia or cryptozoospermia, which cannot be traced to non-genetic sources.

The researchers then compared the sequencing results with the X chromosomes in males without any fertility problems.

In doing so, they were able to identify 21 genes that could be linked to male infertility problems and another 34 genes described as having more modest associations.

The researchers note that this study also allowed them to identify several disease-causing variants of varying degrees of importance, which have been linked to genes identified in the past as associated with male infertility.

The researchers, led by Cecilia Krauses of the University of Florence in Italy, then sequenced samples from another 265 male patients with either azoospermia or cryptozoospermia, this time focusing their attention on the strongest associations they discovered in the first part of their study.

In doing so, they were able to identify specific variants in approximately 6 genes in nine of the patients.

They also looked for similar types of fruit flies with fertility problems, looking for examples of the RBBP7 variant specifically, because it was most common in men – and they also found that it was also more common in fruit flies.

The researchers concluded by suggesting that their work narrows the knowledge gap in the causes of X-linked infertility in male patients.