Question

Which one of the following is NOT true regarding Homocystinuria?

• A. Downward dislocation of lens
• B. Marked osteoporosis
• C. Stroke in young
• D. Autosomal dominant inheritance

Hint:

Three of these are true clinical features - the fourth gets the inheritance pattern wrong.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
Homocystinuria is an inborn error of methionine metabolism, most commonly due to cystathionine beta-synthase deficiency. The question asks which of four statements about it is NOT true.

Step 2: Key Concept or Approach:
Homocystinuria produces a marfanoid body build with several features that overlap with, and some that distinguish it from, true Marfan syndrome: downward or inferior dislocation of the lens (as opposed to the upward dislocation typical of Marfan syndrome), osteoporosis, and a strongly increased risk of arterial and venous thrombosis - including stroke at a young age - because elevated homocysteine damages the vascular endothelium and promotes clotting. Crucially, the inheritance pattern is autosomal recessive, since it takes two defective copies of the cystathionine beta-synthase gene to cause the enzyme deficiency.

Step 3: Working Through the Options:
Downward lens dislocation is a true and classically taught distinguishing feature of homocystinuria. Marked osteoporosis is a true skeletal feature, related to abnormal collagen cross-linking. Stroke in young patients is true, reflecting the pro-thrombotic effect of high homocysteine levels on blood vessels. Autosomal dominant inheritance is false - the disease is inherited in an autosomal recessive pattern.

Step 4: Conclusion:
The correct answer is autosomal dominant inheritance, since homocystinuria is actually an autosomal recessive condition.