Case history
Case history #1
A 2-year-old boy presents with developmental delay and floppiness. Although he is happy and interactive, he is behind in reaching developmental milestones. He rarely turns over, has difficulty holding up his head unsupported for a long time, and is unable to sit independently. He is suspected of having dyskinetic cerebral palsy. When asked, his parents remember sometimes noticing orange "sand" in his diapers in the past. On clinical examination, there is a generalized, severe hypotonia. He displays frequent extraneous movements in his face, neck, and limbs, with twisted and sustained postures that interfere with voluntary movement and are indicative of generalized action dystonia. An MRI of the brain is unremarkable. Metabolic analysis reveals elevated concentrations of uric acid in serum and urine. Hypoxanthine-guanine phosphoribosyltransferase (HPRT) activity is not detectable in cultured fibroblasts. A mutation in the HPRT gene is found.
Case history #2
A 6-year-old boy presents with severe pain in his right flank and lower abdomen, accompanied by nausea. He has also noticed some blood in his urine. His parents report an episode of a red and swollen joint in his left big toe, which was treated with anti-inflammatory agents. Besides severe costovertebral angle tenderness on his right side, a general physical exam is unremarkable. A detailed neurologic exam reveals mild clumsiness and slightly indistinct speech. When performing complicated motor tasks with one hand, the contralateral hand sometimes adopts a mirror posture suggestive of subtle overflow dystonia. Renal ultrasonography confirms nephrolithiasis as the cause of his abdominal pain, and laboratory investigation reveals hyperuricemia. The kidney stone, which passes eventually, shows high urate content. HPRT enzyme activity is 8% of normal.
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