What is the inheritance pattern of friedreich ataxia?
**Core Concept**
Friedreich ataxia is an autosomal recessive genetic disorder caused by an expansion of GAA trinucleotide repeats in the FXN gene, leading to impaired mitochondrial function and progressive neurodegeneration.
**Why the Correct Answer is Right**
Friedreich ataxia follows an autosomal recessive inheritance pattern, meaning that an individual must inherit two copies of the mutated gene (one from each parent) to express the disease. This is because the mutated gene is recessive, and a single copy of the normal gene is sufficient to prevent the disease. The GAA trinucleotide expansion in the FXN gene leads to the production of a truncated frataxin protein, which is essential for mitochondrial iron-sulfur cluster assembly and is crucial for maintaining mitochondrial function. The lack of frataxin results in impaired mitochondrial energy metabolism, leading to neurodegeneration and the characteristic symptoms of Friedreich ataxia.
**Why Each Wrong Option is Incorrect**
* **Option A:** Friedreich ataxia is not an X-linked disorder, as it does not follow a sex-linked inheritance pattern and is not more commonly expressed in males.
* **Option B:** Friedreich ataxia is not a dominant disorder, as an individual must inherit two copies of the mutated gene to express the disease.
* **Option C:** Friedreich ataxia is not a mitochondrial disorder in the classical sense, although it does involve impaired mitochondrial function. However, it is caused by a nuclear gene mutation rather than a mitochondrial DNA mutation.
**Clinical Pearl / High-Yield Fact**
Friedreich ataxia is the most common inherited ataxia and typically presents in late childhood or early adolescence with symptoms of gait ataxia, dysarthria, and areflexia. Early recognition and diagnosis are crucial for the management of this disorder.
**Correct Answer: B. Autosomal recessive**