DO older fathers doom their children to genetic disease? This is the question raised by a new study that says older men produce more gene mutations in the children they sire, boosting their risk of schizophrenia and autism and possibly other diseases.

A father's age is by far the biggest factor determining the rate of new, uninherited genetic mutations in his offspring, according to a paper published in the journal Nature.

From a man's peak reproductive years in adolescence, the rate of new or "de novo" gene mutations triggered at conception in his children rises by about two per year, the study found.

The rate doubles every 16 years, meaning that the baby of a 36-year-old father would have twice as many new mutations than that of a 20-year-old.

"The age of the father is the most important factor to determine the number of new mutations that happen when a child is conceived," study co-author Kari Stefansson from Iceland's DeCODE genetics company told AFP.

Though de novo mutations are not necessarily harmful, it can take only one change in a key gene to cause some types of disease — and the more mutations the higher the risk.

The results from what is claimed to be the biggest-ever study of its kind suggest that disproportionate attention has been paid to the age at which women give birth.

"We have in a very unjust manner been pointing the finger at the old mother when we should have been careful when it comes to the old father. It is clearly dangerous to have an old father," said Stefansson.

Maternal age is linked to Down's syndrome and other chromosomal diseases that develop through a process that is different to the type of genetic mutation described in this study.

The mutations in the Nature report are caused by cell division during processes like sperm production.

Stefansson and a team in Iceland, Denmark and Britain sequenced the genomes of 78 parent-child trios, as well as hundreds of control subjects, looking for variants in the sequence of a child's genetic code that did not exist in the parents.

They found that the rate of increase in de novo mutations could be ascribed to the tune of 97.1 per cent, "maybe entirely", to the age of the father — an outcome that "surprised" the researchers.

— AFP