By Ed Yong Rising levels of male infertility around the world could be linked to an increase in the number of young men suffering from diabetes, according to results presented on Wednesday at the European Society of Human Reproduction and Embryology. A group of researchers from Queen’s University in Belfast, UK, have found that the DNA-repair genes in sperm stem cells of diabetic men are less active, despite the sperm appearing healthy under the microscope. “We have shown that diabetes influences male reproductive function in subtle, previously undetected ways,” says Con Mallidis, who led the study. His group have previously found that the sperm of diabetic men have unusually high levels of DNA damage. Now they have demonstrated that sperm sampled from eight diabetic men show significant changes in the genes involved in repairing this damage. Allan Pacey, of the University of Sheffield, UK, says that the results suggest that the sperm production process was disrupted in some way. This should be checked, he says, since DNA damage could, in theory, lead to disease in children fathered by such men. Mallidis’s study is small, but no large epidemiological studies have looked for links between diabetes and infertility, he says. Mallidis thinks that the common practice in fertility clinics of visually assessing sperm quality could be misleading. “Few clinics even bother to record the diabetic status of the male partner in a couple seeking assistance for infertility,” he claims. It isn’t clear how diabetes leads to DNA damage, but Mallidis thinks the most likely culprits are a class of compounds called advanced glycation end products (AGEs). The team found unusually high levels of these chemicals, which are known to damage DNA by oxidative stress, in the reproductive tracts of diabetics. Diabetes is also associated with a 14-fold decrease in the level of a protective protein called ornithine decarboxylase, which produces compounds such as spermidine and spermine that counteract the effects of AGEs. Mallidis says, “What we have is a body [sperm DNA damage], a bullet [oxidative stress] and a smoking gun [AGEs]. Whether one is the result of the other?