Researchers say a rare form of testicular tumor might help explain why some diseases are more common in the children of older fathers.
The research team from University of Oxford and Copenhagen University Hospital has found a link between certain severe childhood genetic disorders and rare testicular tumors occurring in older men.
Mutations can occur in different cells of the body and at different times during life. Some, such as those, which occur in 'germ cells' (those which create sperm or eggs), cause changes, which affect the offspring.
According to the researchers, the germ cells that make the mutant gene-carrying sperm seem to be the same cells that produce the tumor.
"We think most men develop these tiny clumps of mutant cells in their testicles as they age," Nature magazine quoted lead researcher Professor Andrew Wilkie from the University of Oxford as saying.
"They are rather like moles in the skin, usually harmless in themselves. But by being located in the testicle, they also make sperm - causing children to be born with a variety of serious conditions.
"We call them 'selfish' because the mutations benefit the germ cell but are harmful to offspring," Wilkie added.
The new discovery might provide an insight into the origins of several serious conditions that affect childhood growth and development like achondroplasia and Apert, Noonan and Costello syndromes, as well as some conditions causing stillbirth.
"What we have seen so far may just be the tip of a large iceberg of mildly harmful mutations being introduced into our genome," said Wilkie.
"These mutations would be too weak and too rare to be picked up by our current technology, but their sheer number would have a cumulative effect, leading to disease," he added.
The study appears in journal Nature Genetics.