The importance of salvage pathways in nucleotide metabolism was not appreciated until the discovery of a metabolic disease called the Lesch Nyhan syndrome in the 1960s. This is a rare but famous X-linked disease. Affected boys appear normal at birth. There is a delay in motor development a few months after birth. Affected boys exhibit choreoathetosis (a sign characterized by or flailing arm movements), spasticity, mental retardation, and uric acid overproduction that produces gout. They also are pathologically aggressive toward others and themselves, as shown by self- mutilating behavior. Self-mutilation is evidenced by biting and chewing lips and fingers. The syndrome is caused by an absence of HGPRT activity. Until the elucidation of the mechanism of the Lesch-Nyhan syndrome, scientists did not belive that purine salvage pathways were physiologically important. The severity of this disease, however, provided evidence to the contary.