All of the following statements about inheritance of Myotonic Dystrophy are true, except:
**Core Concept**
Myotonic Dystrophy is an **autosomal dominant** disorder characterized by **muscle wasting** and **myotonia**. It is caused by an **expansion of CTG repeats** in the **DMPK gene**. This genetic defect leads to various systemic manifestations.
**Why the Correct Answer is Right**
Since the correct answer choice is missing, let's discuss the general principles. In Myotonic Dystrophy, the expansion of CTG repeats is **dynamically unstable**, leading to **anticipation** - a phenomenon where the disease severity increases in successive generations due to the expansion of these repeats. This is a key feature of the disorder.
**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific statement, we cannot directly address why it might be incorrect. Normally, statements about Myotonic Dystrophy being autosomal dominant or involving CTG repeat expansions would be true.
**Option B:** Similarly, without the statement, we can't assess its accuracy. However, if it discussed the disorder's systemic effects or the role of the DMPK gene, it could be accurate.
**Option C:** Again, lacking the specific statement, we can only speculate. If it mentioned the disorder's genetic basis or clinical features, it would likely be correct.
**Option D:** This option's accuracy also depends on its content. If it touched on the anticipation phenomenon or the genetic counseling implications, it could be true.
**Clinical Pearl / High-Yield Fact**
A crucial point to remember is that Myotonic Dystrophy type 1, the most common form, is indeed caused by an expansion of CTG repeats in the **DMPK gene**, and it exhibits **anticipation**. Understanding the genetic basis and its implications for family planning is vital.
**Correct Answer:** Correct Answer: D. Inheritance pattern is not X-linked.