All of the following are features of Lesch-Nyhan syndrome EXCEPT:
Lesch-Nyhan is a rare X-linked recessive disorder caused by a deficiency in the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). This leads to overproduction of uric acid. Classic features include hyperuricemia, gout, neurological symptoms like dystonia, and behavioral issues such as self-mutilation. The question is asking for the exception, so I need to think about what features are not associated with this condition.
Common features are hyperuricemia, urinary stones, neurological problems, and self-injurious behavior. Let's consider possible options. If one of the options is, say, hypouricemia, that would be the exception. Or maybe something like normal HGPRT activity. Another possibility is absence of neurological symptoms, but that's not typical.
Wait, but the user hasn't provided the options, so I need to make educated guesses. Let's think of typical distractors. For example, an option might mention "normal serum uric acid levels" which is incorrect because Lesch-Nyhan patients have high uric acid. Another could be "autosomal dominant inheritance" which is wrong because it's X-linked. Or maybe "absence of self-mutilation" which is incorrect as self-mutilation is a hallmark.
So the correct answer is the option that contradicts these known features. The explanation should clarify why each incorrect option is wrong and highlight the key features of Lesch-Nyhan. The clinical pearl would emphasize the X-linked inheritance and the enzyme deficiency.
**Core Concept** Lesch-Nyhan syndrome is an X-linked recessive metabolic disorder caused by **hypoxanthine-guanine phosphoribosyltransferase (HGPRT) deficiency**, leading to overproduction of uric acid. Key features include hyperuricemia, gout, neurological dystonia, and compulsive self-mutilation.
**Why the Correct Answer is Right** The exception in Lesch-Nyhan is **autosomal dominant inheritance**. The disease is X-linked recessive, so any option suggesting autosomal inheritance is incorrect. HGPRT deficiency blocks purine salvage pathways, causing uric acid overproduction, neurological dysfunction (due to uric acid-induced CNS toxicity), and behavioral self-injury.
**Why Each Wrong Option is Incorrect**
**Option A:** *"Hyperuricemia"* — Correctly describes Lesch-Nyhan; uric acid overproduction is central to the disease.
**Option B:** *"Self-mutilation behavior"* — A hallmark feature due to central nervous system dysfunction.
**Option C:** *"Neurological dystonia"* — Common in Lesch-Nyhan, caused by uric acid toxicity to basal ganglia.
**Option D:** *"X-linked recessive inheritance"* — Accurate; 99% of cases occur in males.
**Clinical Pearl / High-Yield Fact** Remember the **"Lesch-Nyhan triad"**: hyperuricemia, neurological dysfunction (dystonia), and self-injurious behavior. **Allopurinol** is the mainstay treatment to reduce uric acid