WASHINGTON — As many as 250,000 veterans of the first Gulf War “have persistent unexplained medical symptoms” whose cause may never be found, although genetic testing and functional brain imaging may eventually shed some light on the problem.

That is one of the conclusions of a new review of research on the constellation of physical complaints originally known as “Gulf War syndrome” experienced by many soldiers soon after the United States drove invading Iraqi forces out of Kuwait in early 1991.

The review, by the National Academy of Science’s Institute of Medicine, found that the only illness clearly caused by the Gulf War is post-traumatic stress disorder, or PTSD. It is present in 2 percent to 15 percent of Gulf War veterans (depending on how it is diagnosed), and about three times more common in them than in soldiers who served at the same time but were deployed elsewhere.

The 12-member panel of medical experts also found “evidence of an association” between Gulf War service and anxiety disorder, alcohol abuse, dyspepsia, irritable bowl syndrome and “multisymptom illness” (its term for Gulf War syndrome) although not clearly a causal one.

An increase in vague symptoms and persistent pain has also been seen in some non-American groups, including British troops who served in the Gulf, and Danish peacekeepers who were there after the war.