Medical Definition of Dementia, MELAS
MELAS is a form of dementia. It is caused by mutations in the genetic material (DNA) in the mitochondria. While most of our DNA is in the chromosomes in the cell nucleus, another important cell structure that carries DNA is the mitochondrion. Much of the DNA within the mitochondrion is used to manufacture proteins that help in the mitochondrion's energy-producing function.
As a result of the disturbed function of their cells' mitochondria, patients with MELAS develop brain dysfunction (encephalopathy) with seizures and headaches, as well as muscle disease with a buildup of lactic acid in the blood (lactic acidosis), temporary local paralysis (strokelike episodes), and abnormal thinking (dementia).
MELAS is diagnosed by muscle biopsy showing characteristic ragged red fibers. Brain biopsy shows stroke-like changes.
MELAS affects persons at different times of life, from 4 to 40s. Most patients show symptoms before 20 years old.
Patients are managed according to which areas of the body are affected at a particular time. There is no known treatment for MELAS which is progressive and fatal.
Mutations (changes) in the mitochondrial chromosome are responsible for a number of disorders including not only MELAS but also for examples:
The mitochondria, as mentioned, are normal structures located outside the nucleus in the cell's cytoplasm. Each mitochondrion has a chromosome made of DNA that is quite different from the better known chromosomes in the nucleus. The mitochondrial chromosome is much smaller; it is round (whereas the chromosomes in the nucleus are normally shaped like rods); there are many copies of the mitochondrial chromosome in every cell; and no matter whether we are male or female, we inherit our mitochondrial chromosome from our mother.
MELAS and all other mitochondrial diseases were entirely enigmatic before it was discovered that they were due to mutations not in regular chromosomes but in the chromosome of mitochondria.
Last Editorial Review: 7/1/2016
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