A 7-year-old girl with normal early development presents with seizures, recurrent stroke-like episodes, episodic vomiting, and sensorineural hearing loss. MRI shows infarcts not confined to vascular territories, and blood lactate is elevated. Muscle biopsy shows subsarcolemmal mitochondrial proliferation. What is the mode of inheritance?

• A Autosomal recessive
• B Autosomal dominant
• C X-linked dominant
• D Maternal (mitochondrial) inheritance ✓

Explanation

The combination of mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes defines MELAS, usually caused by the m.3243A>G point mutation in MT-TL1. Mitochondrial DNA is transmitted exclusively through the ovum, so inheritance is maternal with variable expressivity explained by heteroplasmy. Ragged red fibres reflect subsarcolemmal mitochondrial accumulation. Autosomal and X-linked patterns do not apply to mtDNA point mutations.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.