MELAS syndrome

[2] A feature of these diseases is that they are caused by defects in the mitochondrial genome which is inherited purely from the female parent.

Though less common, infantile onset may occur and may present as failure to thrive, growth retardation and progressive deafness.

Onset in older children typically presents as recurrent attacks of a migraine-like headache, anorexia, vomiting, and seizures.

Increased acidity in the blood can lead to vomiting, abdominal pain, extreme tiredness (fatigue), muscle weakness, loss of bowel control, and difficulty breathing.

MERRF patients may also have hearing loss, visual disturbance secondary to optic atrophy, and short stature.

The characteristic myoclonic seizure in MERRF may help to narrow diagnosis, but genetic testing should be considered to distinguish the two conditions.

[1] Leigh syndrome may also present with progressive neurological deterioration, seizures, and vomiting, mainly in young children.

[5] Some of the genes (MT-ND1, MT-ND5) affected in MELAS encode proteins that are part of NADH dehydrogenase (also called complex I) in mitochondria, that helps convert oxygen and simple sugars to energy.

Less commonly, the disorder results from a new mutation in a mitochondrial gene and occurs in people with no family history of MELAS.

Initial lesions often occur in the occipital or parietal lobes with eventual involvement of the cerebellum, cerebral cortex, basal ganglia, and thalamus.

MR spectroscopy may show an elevated lactate peak in affected and even unaffected brain areas.

Muscle biopsy of a person diagnosed with MELAS but carrying no known mutation. (a) Modified Gomori trichrome stain showing several ragged red fibers (arrowhead). (b) Cytochrome c oxidase stain showing Type-1 lightly stained and Type II fibers, darker fibers, and a few fibers with abnormal collections of mitochondria (arrowhead). Note cytochrome c oxidase negative fibers as usually seen in mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS). (c) Succinate dehydrogenase staining showing a few ragged blue fibers and intense staining in the mitochondria of the blood vessels (arrow). (d) Electron microscopy showing abnormal collection of mitochondria with paracrystalline inclusions (arrowhead), osmiophilic inclusions (large arrowhead) and mitochondrial vacuoles (small arrowhead). [ 7 ]