Question

A family pedigree reveals multiple individuals with symptoms such as progressive eye movement limitation, retinal pigment changes, and disturbances in cardiac conduction. Based on these findings and the inheritance pattern, which of the following is the most probable diagnosis?

• A. Duchenne Muscular Dystrophy
• B. Kearns--Sayre Syndrome
• C. Friedreich Ataxia
• D. Myotonic Dystrophy

Hint:

Progressive external ophthalmoplegia + pigmentary retinopathy + heart block = Kearns--Sayre syndrome.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The clinical triad of Chronic Progressive External Ophthalmoplegia (CPEO), pigmentary retinopathy, and heart block (cardiac conduction defects) is the hallmark of a specific mitochondrial disorder.
Step 2: Detailed Explanation:

Inheritance Pattern: The pedigree shows mitochondrial inheritance (maternal inheritance). Affected females transmit the disease to ALL of their offspring, while affected males transmit it to NONE. This occurs because the mitochondria in the zygote are derived exclusively from the oocyte.

Kearns-Sayre Syndrome (KSS): This is caused by large-scale deletions of mitochondrial DNA (mtDNA). It is a multisystem disorder defined by the triad of: 1. Onset before age 20. 2. Pigmentary retinopathy. 3. CPEO (progressive limitation of eye movements and ptosis).

Critical Feature: Cardiac conduction disturbances (e.g., bundle branch blocks or complete heart block) are the most life-threatening component and require permanent pacemaker placement.

Differential Analysis: Duchenne Muscular Dystrophy is X-linked recessive (primarily affects males). Friedreich Ataxia is autosomal recessive (requires both parents to be carriers). Myotonic Dystrophy is autosomal dominant (vertical transmission from either parent to approx. 50% of kids).

Biochemical Marker: Muscle biopsy often shows "Ragged Red Fibers" on Gomori trichrome stain, indicating subsarcolemmal mitochondrial proliferation.

Step 3: Final Answer:
Given the maternal inheritance pattern in the pedigree and the specific clinical triad, the most probable diagnosis is Kearns–Sayre Syndrome.