Which disorder is caused by an HPRT1 gene mutation and presents with self-injurious behavior along with cognitive impairment and dystonia?

• A. Blepharospasm
• B. Dopa-responsive dystonia
• C. Lesch-Nyhan syndrome
• D. Sydenham chorea

Answer: (C)

Lesch-Nyhan syndrome is the disorder described. It results from mutations in the HPRT1 gene, which encodes the enzyme hypoxanthine-guanine phosphoribosyltransferase involved in purine salvage. When this enzyme is deficient, uric acid builds up (hyperuricemia) and a distinctive neurologic/metabolic picture emerges. The hallmark behavioral feature is self-injurious behavior, often beginning in early childhood, alongside cognitive impairment and movement abnormalities such as dystonia and chorea. Other conditions listed don’t feature the same combination of HPRT1-related deficiency and self-injurious behavior: blepharospasm is a focal dystonia of the eyelids without this genetic-metabolic background; dopa-responsive dystonia typically shows diurnal variation and responds to levodopa; Sydenham chorea follows streptococcal infection and isn’t linked to HPRT1 mutations or self-harm. Thus, the described combination points to Lesch-Nyhan syndrome.