**Question:** Inheritance of Huntington's chorea

**Core Concept:** Huntington's disease is an autosomal dominant disorder caused by an expansion of CAG trinucleotide repeats on the HTT gene, leading to the production of an abnormal huntingtin protein.

**Why the Correct Answer is Right:** Huntington's chorea is an inherited neurological disorder characterized by involuntary movements, cognitive decline, and psychiatric symptoms. The disorder is caused by an expansion of CAG trinucleotide repeats on the HTT gene, which encodes the huntingtin protein. When the number of CAG repeats exceeds 36, it leads to the production of an abnormal huntingtin protein, causing the disease.

**Why Each Wrong Option is Incorrect:**

A. Dominantly inherited disorders can have autosomal, X-linked, or mitochondrial inheritance patterns. In this case, the correct answer is autosomal dominant inheritance.

B. Mitochondrial disorders are caused by genetic mutations in mitochondrial DNA, not nuclear DNA like in Huntington's disease.

C. X-linked disorders are inherited through the X chromosome, which is not applicable to Huntington's disease.

D. Recessive disorders are caused by mutations that require two copies of the mutated allele for expression. Huntington's disease is an autosomal dominant disorder.

**Clinical Pearl:** Understanding the inheritance pattern of genetic disorders is crucial for counseling and predicting the risk of affected offspring in families with a history of these conditions. In cases of autosomal dominant disorders like Huntington's disease, every child of an affected individual has a 50% chance of inheriting the disease.

**Correct Answer:** D. Autosomal Dominant

In conclusion, Huntington's chorea is an autosomal dominant disorder due to the inheritance pattern of the disease-causing mutation on the HTT gene. Understanding the inheritance pattern helps predict the risk of affected offspring and provides valuable information for genetic counseling.