Inheritance: X-linked recessive
Genetic locus: Xq26-q27
Clinical findings:
(1) neurologic disability
(1a) marked delay in motor development with hypotonia and spasticity (which may not be detected until several months of age)
(1b) extrapyramidal dysfunction with dystonia, choreoathetosis and/or ballismus
(1c) pyramidal dysfunction with hyperreflexia and extensor plantar response (positive Babinski sign)
(1d) dysarthria
(2) cognitive disability (may be normal)
(3) behavioral problems with self-mutilation
(3a) biting of tongue, lips, fingers or other body parts
(3b) head banging or snapping
(3c) eye poking
(3d) activities damaging to fingers and/or extremities
(4) gouty arthritis
(5) uric acid and/or hypoxanthine nephrolithiasis, with urinary tract infection and renal insufficiency
(6) growth retardation
(7) dysphagia and emesis, with risk of aspiration
(8) fevers due to infection and/or joint inflammation and/or respiratory infection
The patient may have a sibling with similar findings.
Laboratory findings:
(1) hyperuricemia and hyperuricosuria, with elevation in the urine urate to creatinine ratio
(2) markedly reduced HPRT activity (< 1.5% residual activity)
(3) megaloblastic anemia
(4) biochemical evidence of renal insufficiency
