Question

The chromosome involved in myotonic dystrophy is

• A. Chromosome 19
• B. Chromosome 20
• C. Chromosome 21
• D. Chromosome 22

Hint:

Recall the CTG repeat in the DMPK gene at 19q13.

Answer 1

The Correct Option is A

Step 1: Identify the disease class - myotonic dystrophy is a trinucleotide-repeat expansion disorder. Step 2: The expanded $CTG$ repeat sits in the DMPK gene, which is mapped to band $19q13.3$. Step 3: This expansion explains the clinical triad of distal weakness, type I fibre atrophy and the inability to quickly relax a gripped hand (myotonia), with anticipation across generations as the repeat lengthens. Step 4: None of the other listed chromosomes (20, 21, 22) carry the DMPK locus, so by elimination and direct mapping the answer is chromosome 19.\[\boxed{\text{Chromosome 19}}\]