MELAS=The syndrome of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes
An A-to-G transition in the mitochondrial transfer RNA Leu(UUR) gene at base pair 3243 has been shown to be associated with maternally transmitted diabetes and sensorineural hearing loss. In other subjects, this mutation is associated with diabetes and the syndrome of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS syndrome). The mitochondrion plays a key role in the regulation of insulin secretion, particularly in response to glucose.
MELAS is a maternally inherited multisystemic disorder caused by mutations of mitochondrial DNA. The hallmark is the occurrence of stroke-like episodes that result in hemiparesis, hemianopia, or cortical blindness. Other common features include focal or generalized seizures, recurrent migraine-like headaches, vomiting, short stature, hearing loss, and muscle weakness. 80 percent of cases are related to the A3243G mutation and 10 percent to the T3271C transfer RNA mutation.
MELAS usually manifests in childhood after a normal early development [46,47,50]. A relapsing-remitting course is most common, with stroke-like episodes leading to progressive neurologic dysfunction and dementia.
The diagnostic criteria required:
--stroke-like episodes before age 40 years,
--encephalopathy characterized by seizures or dementia,
--either blood lactic acidosis or the presence of ragged red fibers in skeletal muscle biopsy
However, a broader range of phenotypes is now recognized as compatible with the diagnosis, including clinical onset after age 40.
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