Okay, let's tackle this question about the inheritance of Huntington's chorea. First, I need to recall the genetic basis of this condition. Huntington's disease is a neurodegenerative disorder, right? I remember it's related to a trinucleotide repeat expansion.

So the core concept here is the mode of inheritance. Huntington's is an autosomal dominant disorder. That means only one copy of the mutated gene is sufficient to cause the disease. The gene involved is HTT, which codes for huntingtin protein. The mutation is a CAG trinucleotide repeat expansion in the HTT gene. Normal individuals have fewer than 36 repeats, while affected individuals have 36 or more. The more repeats, the earlier the onset and more severe the disease.

The correct answer should be autosomal dominant. Let me check the options again. The user didn't provide the options, but typical distractors might include autosomal recessive, X-linked dominant, or maybe something else. For example, if an option says autosomal recessive, that's wrong because the disease doesn't require two copies. X-linked would also be incorrect because it's not on the X chromosome. Mitochondrial inheritance is out of the question here since it's a nuclear gene mutation.

Clinical pearl: Huntington's is a classic autosomal dominant disorder with complete penetrance. The trinucleotide expansion leads to an expanded polyglutamine tract in the huntingtin protein, causing neuronal dysfunction and death, particularly in the striatum and cortex. Genetic testing is available, and pre-symptomatic testing is an option for at-risk individuals.

Now, structuring the explanation. The Core Concept should state it's autosomal dominant due to the HTT gene mutation. The correct answer explanation would detail the CAG repeats and the dominant inheritance pattern. The wrong options would be addressed by explaining why they don't fit. The clinical pearl should highlight the key inheritance and the genetic mechanism. Finally, the correct answer line needs to be clear.

**Core Concept**
Huntington's chorea (Huntington's disease) is an **autosomal dominant neurodegenerative disorder** caused by a **CAG trinucleotide repeat expansion** in the **HTT gene** on chromosome 4. The mutated protein forms toxic aggregates, leading to progressive striatal and cortical neuronal loss.

**Why the Correct Answer is Right**
Huntington’s disease follows **autosomal dominant inheritance** with **complete penetrance**. A single mutant allele of the **HTT gene** (encoding huntingtin protein) is sufficient to cause disease. The pathogenic CAG repeat (>35 repeats) results in a polyglutamine tract that disrupts protein function and triggers apoptosis in neurons, particularly in the **caudate nucleus** and **putamen**. This mechanism distinguishes it from recessive or X-linked disorders.

**Why Each Wrong Option is Incorrect**
**Option A:** *Autosomal recessive* is incorrect because Huntington’s requires only one mutant allele for disease manifestation.
**Option B:** *X-linked dominant* is incorrect as the HTT gene is on an autosome (chromosome 4), not the X chromosome.
**Option D:** *Mitochondrial inheritance* is incorrect because mutations in nuclear DNA (not mitochondrial DNA) cause this disease.

**Clinical Pearl / High-Yield Fact**
Always associate

✓ Correct Answer: A. AD