A 2-year-old boy presents with progressive lactic acidosis, failure to thrive, and hypotonia. Plasma lactate-to-pyruvate (L:P) ratio is markedly elevated (>30). MRI shows symmetric bilateral lesions in the basal ganglia and brainstem. Muscle biopsy shows cytochrome c oxidase (complex IV) deficiency. This clinical syndrome is known as:
- A MELAS syndrome (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes)
- B Leigh syndrome (subacute necrotising encephalomyelopathy) ✓
- C Kearns-Sayre syndrome
- D Leber hereditary optic neuropathy (LHON)
Explanation
Leigh syndrome is a heterogeneous mitochondrial disorder characterised by subacute necrotising encephalomyelopathy with bilateral symmetric lesions in the basal ganglia and brainstem on MRI, severe lactic acidosis with elevated L:P ratio (reflecting impaired pyruvate oxidation), and progressive neurodegeneration. It can result from mutations in complex I, II, IV, or pyruvate dehydrogenase/ATP synthase components — both mitochondrial and nuclear encoded. Complex IV (COX) deficiency is among the most common causes. MELAS involves stroke-like episodes with ragged-red fibres (m.3243A>G). Kearns-Sayre involves external ophthalmoplegia, pigmentary retinopathy, and heart block. LHON causes painless bilateral visual loss in young males.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
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Written and medically reviewed by the StethoPrep medical team.