CHICAGO (AFP) -- Most apparently random cases of autism may be just that, a function of freak genetic accidents, rather than a product of an inherited genetic predisposition that is passed down through generations, according to a new study.

The authors of the study suggest that spontaneous mutations in the DNA of an afflicted child or their parent may play a much larger role than previously thought in sporadic cases of autism, where there is no family history of the devastating childhood developmental disorder. The genetic origins of the neurological condition are still unclear, but in a recent paper, U.S. researchers reported that spontaneous mutations, or tiny glitches in the DNA, were common in about 10 percent of the autistic patients they studied. The pattern was particularly noticeable in cases of sporadic autism which is the most common form. In the light of this finding, investigators at Cold Spring Harbor Laboratory and Albert Einstein College of Medicine in New York did a mathematical analysis of three databases on the incidence of autism to see if this new theory could account for the distribution of cases. They concluded that a previously unrecognized pattern could be explained by assuming that spontaneous mutations are a significant cause of the disorder and that parents, especially women, who acquire the DNA glitches, have a 50 percent chance of passing it on to their child. The researchers suggest that in this way, women who carry these spontaneous mutations, which are in effect missing or duplicate stretches of DNA, while themselves asymptomatic, are the source of high-risk families, which feature one or more autistic children. ""For the first time, we have a model that explains the sporadic and the inherited forms of autism,"" said Michael Wigler, a geneticist at Cold Spring Harbor Laboratory. Given that spontaneous mutations in DNA increase with age, and that many women in industrialized nations are postponing childbirth until the last minute, the theory may also explain why older parents are at greater risk of having autistic children, Wigler said. The little-understood disorder is characterized by poor social and communication skills and afflicts one in 150 children, most of them boys, according to the latest estimates from U.S. public health authorities. The study appears in the Proceedings of the National Academy of Sciences