Inheritance pattern of myotonic dystrophy is ?
**Core Concept**
Myotonic dystrophy is a genetic disorder characterized by progressive muscle wasting and weakness, with an autosomal dominant pattern of inheritance. This means that a single copy of the mutated gene is sufficient to cause the condition, and each child of an affected parent has a 50% chance of inheriting the mutated gene.
**Why the Correct Answer is Right**
Myotonic dystrophy is caused by an expansion of a CTG repeat in the DMPK gene on chromosome 19. This expansion leads to the production of an abnormal protein that disrupts muscle function. The autosomal dominant pattern of inheritance means that a single copy of the mutated gene is enough to cause the condition, and each child of an affected parent has a 50% chance of inheriting the mutated gene. This is in contrast to autosomal recessive conditions, where two copies of the mutated gene are required to cause the condition.
**Why Each Wrong Option is Incorrect**
* **Option A:** Autosomal recessive pattern of inheritance is incorrect because myotonic dystrophy requires only one copy of the mutated gene to cause the condition.
* **Option B:** X-linked pattern of inheritance is incorrect because myotonic dystrophy is not linked to the X chromosome.
* **Option C:** Mitochondrial pattern of inheritance is incorrect because myotonic dystrophy is not caused by mutations in mitochondrial DNA.
**Clinical Pearl / High-Yield Fact**
Myotonic dystrophy is the most common form of muscular dystrophy in adults, and it is often misdiagnosed as other conditions such as multiple sclerosis or peripheral neuropathy.
**Correct Answer:** C. Autosomal dominant