Question

A 25-year-old man presents for a routine physical examination. The patient is tall and on examination he was found to have an early diastolic murmur. His family pedigree is given below. Which of the following is the mode of inheritance by which the disease is likely to be transmitted?

• A. AD
• B. AR
• C. XLR
• D. XLD

Hint:

Trace the pedigree: trait in every generation with male-to-male transmission narrows it to one pattern.

Answer 1

The Correct Option is A

Step 1: A tall young man with an early diastolic murmur points to aortic regurgitation from aortic root dilatation, classically seen in Marfan syndrome (a fibrillin-1 connective tissue disorder).

Step 2: Read the pedigree. The trait appears in every generation, affects males and females equally, and there is at least one instance of male-to-male (father-to-son) transmission. That combination rules out X-linked inheritance and recessive patterns.

Step 3: Vertical transmission through every generation with an affected parent passing the trait to roughly half the children is the hallmark of autosomal dominant (AD) inheritance. The mutated gene expresses itself in the heterozygous state, and AD disorders typically affect structural or non-enzyme proteins (here, fibrillin), with variable expressivity and reduced penetrance.

So the inheritance is AD.

Ref: Robbins Basic Pathology, 9e.