Question

Which one of the following is NOT true in the case of myotonic dystrophy?

• A. Cardiac defects
• B. Cataract
• C. Enlarged testis
• D. Frontal baldness

Hint:

Think about what actually happens to gonadal size in this disease, not what you might expect.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question tests recognition of the classic multisystem features of myotonic dystrophy (dystrophia myotonica) and asks which listed feature is actually false for this condition.

Step 2: Key Concept or Approach:
Myotonic dystrophy is an autosomal dominant trinucleotide repeat disorder (CTG repeat in the DMPK gene) that causes myotonia along with a distinctive pattern of extramuscular findings: cardiac conduction defects and arrhythmias, early posterior subcapsular cataracts, frontal balding in men, and gonadal atrophy. The key discriminator here is testicular size -- the disease causes testicular atrophy with hypogonadism, not enlargement.

Step 3: Working Through the Options:
Cardiac defects are genuinely true -- conduction system disease, heart block, and arrhythmias are major and potentially fatal features requiring cardiac monitoring. Cataract is genuinely true -- subcapsular "Christmas tree" cataracts are a well-known early sign, sometimes preceding muscle symptoms. Enlarged testis is false -- myotonic dystrophy causes testicular atrophy and androgen deficiency, the opposite of enlargement, which is why this is the correct answer to "NOT true." Frontal baldness is genuinely true -- early frontal balding in affected men is one of the most recognizable external features of the disease.

Step 4: Conclusion:
The correct answer is enlarged testis, since myotonic dystrophy causes testicular atrophy, not enlargement.