Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes
OMIM	540000
DiseasesDB	8254
MeSH	D017241

Overview

Mitochondrial myopathy, encephalopathy, lactic acidosis, stroke-like episodes, abbreviated to MELAS is one of the family of mitochondrial cytopathies, which also include MERRF, and Leber's Hereditary Optic Atrophy. A feature of these diseases is that they are caused by defects in the mitochondrial genome which is inherited purely from the female parent. The disease can manifest in both sexes.

Pathophysiology

Genetics

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes is a condition related to changes in mitochondrial DNA. Mutations in the MT-ND1, MT-ND5, MT-TH, MT-TL1, and MT-TV genes cause mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes. The genes associated with MELAS are contained in mitochondrial DNA. Some of the genes related to MELAS provide instructions for making proteins involved in normal mitochondrial function. These proteins are part of a large enzyme complex in mitochondria that helps convert oxygen and simple sugars to energy. Other genes associated with this disorder provide instructions for making molecules called transfer RNAs (tRNAs), which are chemical cousins of DNA. These molecules help assemble protein building blocks called amino acids into full-length, functioning proteins within mitochondria.

Mutations in a particular transfer RNA gene, MT-TL1, cause more than 80 percent of all cases of MELAS. These mutations impair the ability of mitochondria to make proteins, use oxygen, and produce energy. Researchers have not determined how changes in mitochondrial DNA lead to the specific signs and symptoms of MELAS. They continue to investigate the effects of mitochondrial gene mutations in different tissues, particularly in the brain.

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.

Natural History, Complications and Prognosis

Prognosis

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.

Diagnosis

History and Symptoms

MELAS is a condition that affects many of the body's systems, particularly the brain and nervous system (encephalo-) and muscles (myopathy). In most cases, the signs and symptoms of this disorder appear in childhood following a period of normal development. Early symptoms may include

• Muscle weakness
• Muscle pain
• Recurrent headaches
• Loss of appetite
• Vomiting
• Seizures
• Abdominal pain
• Extreme tiredness (fatigue)
• Difficulty breathing

Physical Examination

Eye

• Vision abnormalities

Ear

• Hearing loss

Extremeties

• Myoclonus

Neurologic

• Stroke-like episodes beginning before age 40
• Temporary muscle weakness on one side of the body (hemiparesis)
• Altered consciousness
• Ataxia
• Seizures
• Dementia

Laboratory Findings

Most people with MELAS have a buildup of lactic acid in their bodies, a condition called lactic acidosis.