Treatment: No known cure is available, and there is no effective therapy. Physical therapy and joint replacement increase flexibility and range of motion and help to decrease morbidity. Some researchers advocate a diet low in phenylalanine and tyrosine, although the success of this approach is anecdotal at best. The National Institutes of Health is currently studying an inhibitor of the enzyme 4-hydroxyphenylpyruvic acid dioxygenase, which would decrease the production of homogentisic acid and theoretically help to decrease joint destruction.