Transcript Mitochondrial Encephalomyopathy with Lactic Acidosis and

Mitochondrial
Encephalomyopathy with Lactic
Acidosis and Stroke-like
Episodes
(MELAS)
What is MELAS?
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Mitochondrial = Mutation in the mitochondria
Encephalo- = Occurs in the head
Myopathy = General term for muscle disease
Lactic Acidosis = The blood gets too acidic
Stroke-like Episodes = Brain-related
symptoms of bleeding or blockage
Characteristics
• It is the most common maternally inherited
mitochondrial disease
• Clinical Features: Strokes, myopathy,
muscle twitching, dementia, and deafness
• To a lesser extent: vomiting, migrainelike
headaches, diabetes, droopy eyelids,
muscle weakness, and short stature
More Characteristics
• MELAS affects no specific race or gender
more so than others
• Presentation of the disease occurs with
the first stroke-like episode (usually 14-15
yrs of age)
• This is a progressive disorder with a high
mortality rate
How does MELAS work?
• Abnormal mitochondria do not metabolize
pyruvate
• Excess pyruvate is reduced to lactic acid
which accumulates in blood and other
fluids
• Large clumps of abnormal mitochondria
form in the walls of small arteries and
capillaries in the brain and muscles
What causes MELAS?
• There are at least 6 different point
mutations associated with MELAS
• 80% of cases have a A to G point mutation
in the tRNA (Leu) gene at bp 3243
• 7.5% of cases have a T to C point mutation
in the tRNA (Leu) gene at bp 3271
Causes (contd.)
• All of these mutations are heteroplasmic
• Heteroplasmic = within a single cell, there
is a mixture of mitochondria, some
containing mutant DNA and some
containing normal DNA
• This feature of mitochondrial diseases
might offer a solution to the varied rates of
progression and onset of the disease
References
• Scaglia, Fernando, MD. MELAS
Syndrome.
http://www.emedicine.com/ped/topic1406.
htm. October 26, 2004
• http://herkules.oulu.fi/isbn9514255674/htm
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