NARP syndrome a disorder of –
**Core Concept**
NARP syndrome is a rare genetic disorder characterized by a defect in the mitochondrial DNA. It is caused by a mutation in the MT-ATP6 gene, which encodes a subunit of the mitochondrial ATP synthase enzyme. This defect affects the production of adenosine triphosphate (ATP), leading to impaired energy metabolism in cells.
**Why the Correct Answer is Right**
NARP syndrome is a maternally inherited disorder, meaning it is passed down from the mother to her offspring through the mitochondrial DNA. The MT-ATP6 gene mutation leads to impaired ATP production in the mitochondria, resulting in a decrease in energy metabolism. This energy deficiency affects various tissues, particularly the nervous system, leading to symptoms such as peripheral neuropathy, muscle weakness, and visual impairment.
**Why Each Wrong Option is Incorrect**
**Option A:** Mitochondrial myopathies are a group of disorders caused by defects in the mitochondrial DNA, but they are not the same as NARP syndrome.
**Option B:** Kearns-Sayre syndrome is another mitochondrial disorder caused by a large deletion in the mitochondrial DNA, but it is distinct from NARP syndrome.
**Option C:** MELAS syndrome is a mitochondrial disorder caused by a mutation in the MT-TL1 gene, which encodes a transfer RNA molecule. While it shares some similar symptoms with NARP syndrome, it is a separate disorder.
**Clinical Pearl / High-Yield Fact**
NARP syndrome is a rare disorder, but it is an important consideration in patients with unexplained peripheral neuropathy or muscle weakness, particularly in those with a family history of similar symptoms.
**Correct Answer: D. Mitochondrial disorders. NARP syndrome is a disorder of mitochondrial disorders.**