MELAS

Definition: Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is a syndrome caused by mitochondrial abnormalities, in which children have acute episodes of neurologic dysfunction, cognitive changes, and evidence of muscle involvement with weakness and lactic acidosis.

The stroke-like episodes that give the syndrome its name are often reversible deficits that do not correspond well to specific vascular territories. Pathologically, areas of infarction are observed, often with vascular proliferation and focal calcification.

This syndrome is associated with mutations involving a different mitochondrial tRNA. Metabolic abnormalities are present in cerebral vessels, which may underlie the stroke-like episodes.

Synopsis

 mitochondrial encephalomyopathy
 lactic acidosis
 stroke
 rare glomerulopathy (11506292)

Etiology

 mitochondrial DNA mutations of the MTTL1 gene (mitochondrial transfer RNA leucine 1)

• The mitochondrial tRNA for leucine (UUR) is encoded by nucleotides 3230-3304. (In UUR, R = A or G.)
• The uridine in the wobble position of the anticodon of MTTL1 is modified to taurinomethyluridine.
• MTTL1 containing the 3243A-G (MIM.590050) or 3271T-C (590050.0002) mutations, both of which result in MELAS syndrome (MIM.540000), lack this modification.

References

 Matsumoto J, Saver JL, Brennan KC, Ringman JM. Mitochondrial encephalomyopathy with lactic acidosis and stroke (MELAS). Rev Neurol Dis. 2005 Winter;2(1):30-4. PMID: 16400302

 Jacobs HT, Holt IJ. The np 3243 MELAS mutation: damned if you aminoacylate, damned if you don’t. Hum Mol Genet. 2000 Mar 1;9(4):463-5. PMID: 10699169