Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is a condition that affects many of the body’s systems, particularly the brain and nervous system (encephalo-) and muscles (myopathy). The signs and symptoms of this disorder most often appear in childhood following a period of normal development, although they can begin at any age.
Early symptoms may include muscle weakness and pain, recurrent headaches, loss of appetite, vomiting, and seizures.
Most affected individuals experience stroke-like episodes beginning before age 40. These episodes often involve temporary muscle weakness on one side of the body (hemiparesis), altered consciousness, vision abnormalities, seizures, and severe headaches resembling migraines.
Repeated stroke-like episodes can progressively damage the brain, leading to vision loss, problems with movement, and a loss of intellectual function (dementia).
Most people with MELAS have a buildup of lactic acid in their bodies, a condition called lactic acidosis. Increased acidity in the blood can lead to vomiting, abdominal pain, extreme tiredness (fatigue), muscle weakness, and difficulty breathing.
Less commonly, people with MELAS may experience involuntary muscle spasms (myoclonus), impaired muscle coordination (ataxia), hearing loss, heart and kidney problems, diabetes, and hormonal imbalances.
What causes MELAS?
MELAS syndrome 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, some of our DNA is in another important structure called the mitochondrion (plural: mitochondria).
The mitochondria are 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 all of our mitochondrial chromosome from our mother.
Much of the DNA in our mitochondria is used to manufacture proteins involved in the key function of mitochondria — to produce energy and power the cells in our body.
How common is MELAS?
The exact incidence of MELAS is unknown. It is one of the more common conditions in a group known as mitochondrial diseases. Together, mitochondrial diseases occur in about 1 in 4,000 people.
What are the symptoms of MELAS?
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 build-up of lactic acid in the blood (a condition called lactic acidosis), temporary local paralysis (stroke-like episodes), and abnormal thinking (dementia).
How is MELAS diagnosed?
The diagnosis of MELAS is usually suspected on clinical grounds. However, confirmation of the diagnosis usually requires a muscle or brain biopsy.
The muscle biopsy shows characteristic ragged red fibers; a brain biopsy shows stroke-like changes.
When do people with MELAS develop symptoms?
MELAS can affect people at very different times in life, ranging from age 4 to age 40 or more. However, most patients with MELAS syndrome show symptoms before they are 20 years old.
How is MELAS treated?
There is no known treatment for the underlying disease, which is progressive and fatal.
Patients are managed according to what areas of the body are affected at a particular time. antioxidants and vitamins have been used, but there have been no consistent successes reported.
Are there other mitochondrial diseases?
Yes, mutations (genetic changes) in the mitochondrial chromosome are responsible for a number of other disorders aside from MELAS such as:
- an important eye disease called Leber hereditary optic atrophy;
- a type of epilepsy called MERRF which stands for Myoclonus Epilepsy with Ragged Red Fibers; and
- a neuromuscular disease called the Kearns-Sayre syndrome.
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 the mitochondria.
How do people inherit MELAS?
This condition is inherited in a mitochondrial pattern, which is also known as maternal inheritance. This pattern of inheritance applies to genes contained in mitochondrial DNA.
Because egg cells, but not sperm cells, contribute mitochondria to the developing embryo, only females pass mitochondrial conditions to their children.
Mitochondrial disorders can appear in every generation of a family and can affect both males and females, but fathers do not pass mitochondrial traits to their children.
In most cases, people with MELAS inherit an altered mitochondrial gene from their mother. Less commonly, the disorder results from a new mutation in a mitochondrial gene and occurs in people with no family history of MELAS.