This is the VOA Special English Health Report.

Scientists are trying to better understandautism. The National Institute of Mental Health in Bethesda, Maryland, recently announced the start of three major studies of autism.

Autistic children experience delays in the development of social and communication skills. They may also show limited interests and repeat the same actions over and over.

Autism generally appears by the age of three. It is part of a larger group of disorders, often called autism spectrum disorders. Others include Asperger's syndrome and pervasive developmental disorder.

One of the three new studies will define differences in autistic children with different developmental histories. Another will measure the effectiveness of an antibiotic medicine as a treatment for one kind of autism. And the third study will examine if chelation treatment is effective against autism.

Chelation removes heavy metals from the blood; for example, in cases of lead poisoning. But many parents seek this treatment for autistic children. They believe that many cases of autism were caused by vaccines that contained thimerosal, a mercury-based preservative. That theory is debated.

Institute officials note that chelation does not target mercury alone. It can also remove minerals that the body needs, such as calcium, iron and zinc.

Researchers will do a controlled study to test the effectiveness and safety of chelation for children with autism spectrum disorders.

Institute officials say these disorders are currently reported to affect as many as six out of every 1,000 children.

In an unrelated study, scientists have reported that a man's age could affect the chances that his children will develop autism. The study found that men age forty and older had autistic children almost six times as often as fathers under the age of thirty.

Men in their thirties were about one and one-half times more likely to father an autistic child as dads in their twenties and teen years.

The study, in children born in Israel in the nineteen eighties, found no link between autism and older mothers. The findings appeared in the Archives of General Psychiatry.

And that's the VOA Special English Health Report, written by Caty Weaver. Internet users can learn more about health issues and download archives of our reports at www.unsv.com. I'm Steve Ember.

autism : 孤独症