Scientists may have discovered the reason why older men are at greater risk than younger men of fathering a child who develops serious health problems such as congenital deformities, autism, or schizophrenia.
Researchers at Oxford University have found that older men are more likely to harbour a rare form of testicular tumour which may also cause genetic mutations in the DNA of their children, who inherit the faults through their father's sperm. Professor Andrew Wilkie, who led the study published in the journal Nature Genetics, said that clumps of tumour-producing cells form in the testicular tissue which produces the "germ cells" that give rise to sperm.
"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," Professor Wilkie said. "But by being located in the testicle, they also make sperm, causing children to be born with a variety of serious conditions."
Professor Wilkie said that the latest study, which was funded by the Wellcome Trust, could help to explain the origin of several serious conditions affecting children, including achondroplasia, which is commonly known as dwarfism, as well as stillbirths.
The work may also help scientists to find the many genes that are involved in common diseases where there is a strong genetic component, such as autism and schizophrenia.
Until recently, it was assumed that only women have to worry about having children in later life but a number of studies in the past decade have shown that as the quality of a man's sperm decreases with age, the risk of him fathering a child with serious health problems increases.
The overall risk for an older father of having a child with a birth defect is estimated to be about 4 per cent, compared with a "background" risk of about 3 per cent. One study carried out in Israel suggested that men who became fathers at the age of 40 or older were nearly six times as likely to have a child with autism compared with men younger than 30 when they became fathers.
Research into schizophrenia suggests that the risk of the illness doubled among the children of older fathers compared with the children of men who became fathers in their 20s.
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