Testicular tumors may explain why some diseases are more common in children of older fathers

A rare form of testicular tumour has provided scientists with new insights into how genetic changes (mutations) arise in our children. The research, funded by the Wellcome Trust and the Danish Cancer Society, could explain why certain diseases are more common in the children of older fathers.

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; those which occur in other cells can lead to tumours, but are not inherited.

In work published today in Nature Genetics, researchers at the University of Oxford and Copenhagen University Hospital describe a surprising link between certain severe childhood genetic disorders and rare testicular tumours occurring in older men: the germ cells that make the mutant gene-carrying sperm seem to be the same cells that produce the tumour.

Although the original mutations occur only rarely in the sperm-producing cells, they encourage the mutant cells to divide and multiply. When the cell divides, it copies the mutation to each daughter cell, and the clump of mutant sperm-producing cells expands over time. Hence, the number of sperm carrying this mutation also increases as men get older, raising the risk to older fathers of having affected children.

Professor Andrew Wilkie from the University of Oxford, who led the study, explains: "We think most men develop these tiny clumps of mutant cells in their testicles as they age. 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."