- Defective purine salvage due to absent HGPRT, which concerts hypoxanthine to IMP and guanine to GMP. Results in excess uric acid production and de novo purine synthesis

- X-linked recessive

- intellectual disability, self-mutilation, aggression, hyperuricemia, gout, dystoniaH: HyperuricemiaG: GoutP: Pissed off (agression, self-mutilation)R: RetardationT: DysTonia

- orange crystals in diapers (sodium urate)

Treatment: allopurinol or febuxostat