WASHINGTON — Increasing evidence ties pesticides and other chemicals to some, not all, of the Gulf War illnesses that afflict thousands of veterans of the 1991 war, says an analysis published Monday.

Nearly 30 percent of troops who took part in the brief war have reported symptoms that include fatigue, memory loss, pain and difficulty sleeping.

Citing the variety of symptoms, the Institute of Medicine in 2006 declared there is no single Gulf War syndrome, although troops who served in the Persian Gulf were sicker than those who didn't.

Multiple chemical exposures have long been chief suspects. So Dr. Beatrice Golomb of the University of California, San Diego, reviewed 115 studies of neurological symptoms and veterans' exposure to three related chemicals: the anti-nerve gas pyridostigmine bromide, or PB, given to troops at the time; pesticides used aggressively to control sand flies; and the nerve gas sarin.

Those chemicals belong to a family known as acetylcholinesterase inhibitors that work the same way in the body, she wrote Monday in Proceedings of the National Academy of Sciences.

Among the evidence Golomb cites: Veterans who are genetically less able to clear this type of chemical from their bodies had a higher chance of suffering symptoms, which mirror problems reported by pesticide-exposed agriculture workers.