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This 18 month old girl had global developmental delay, hypotonia, bilateral ptosis, left ventricular hypertrophy, chronic lactic acidosis and neutropenia. MRI of brain revealed bilateral T2/FLAIR intensity within thalami, globus pallidus and putamen with mitochondrial disorder high on the differential diagnosis, either Kerns-Sayre Syndrome or Leigh Syndrome. Molecular genetic analysis revealed a homozygous mutation E140K in SCO2 gene (complex IV of cytochrome c oxidase) and confirms the diagnosis of Leigh Syndrome.
Leigh syndrome is one of the most common mitochondrial disorders, caused by a number of mutations in genes involved in cellular respiration. It is either autosomal recessive or mitochondrial in inheritance. The resulting derangements of neuromuscular function are severe.
The electron microscopy from the left ventricle cardiomyocyte (readily evaluated for mitochondria) demonstrates a number of mitochondria of similar size and shape. There is one extremely enlarged mitochondrion with duplication of cristae, which is a classic ultrastructural feature of the disease. Molecular genetic testing confirmed the diagnosis of Leigh Syndrome.