LOS ANGELES – Men who become fathers later in life pass on more brand-new genetic mutations to their offspring, a study has found — probably contributing to disorders such as autism and schizophrenia in the next generation.

The finding, published online Wednesday in the journal Nature, buttresses earlier observations that rates of autism and some other disorders are more prevalent in children born of older fathers, sometimes by a factor of two or more, experts said. Although this has been observed for years from population studies, scientists had not known what lay behind it.

The new research, made possible by recent advances in DNA-sequencing technology, also should help correct an overemphasis on the riskiness of women giving birth at older ages, some researchers said.

Although older mothers are at higher risk for complications such as diabetes during pregnancy and are more likely to have children with chromosomal disorders such as Down syndrome, the study found that practically all of the new mutations detected in children came from the father.

And the older the father, the more mutations he passed on.

A man aged 29.7 at the time he fathered a child contributed 63 new mutations on average to his offspring, the authors found, and a man age 46.2 contributed double the amount –126 — the authors calculated.

Many of the mutations would confer no effect either for good or ill on the children, scientists noted. But some would — and that is significant because in developed countries there has been a shift over the decades toward older men fathering children, said study senior author Dr. Kari Stefansson.

Stefansson, a human geneticist at the University of Iceland and the company deCODE Genetics in Reykjavik, noted that the average age of Iceland’s fathers at the time of a child’s conception was 34.9 in 1900; 27.9 in 1980; and back up to 33 in 2011.

“Similar changes have taken place all over the Western world,” Stefansson said.