National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) affects many parts of the body, particularly the brain and nervous system (encephalo-) and muscles (myopathy). Symptoms typically begin in childhood and 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. People with MELAS can also have a buildup of lactic acid in their bodies that can lead to vomiting, abdominal pain, fatigue, muscle weakness, and difficulty breathing. The genes associated with MELAS are located in mitochondrial DNA and therefore follow a maternal inheritance pattern (also called mitochondrial inheritance). MELAS can be inherited from the mother only, because only females pass mitochondrial DNA to their children. In some cases, MELAS results from a new mutation that was not inherited from a person's mother.[1]
Last updated: 12/3/2013
The signs and symptoms of MELAS often appear in childhood following a period of normal development. 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 may involve temporary muscle weakness on one side of the body, 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.[1]

Many people with MELAS have a buildup of lactic acid in their bodies (lactic acidosis). This can lead to vomiting, abdominal pain, extreme fatigue, muscle weakness, and difficulty breathing. Involuntary muscle spasms, impaired muscle coordination, hearing loss, heart and kidney problems, diabetes, and hormonal imbalances may also occur.[1]

Last updated: 12/3/2013

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

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Medical Terms Other Names
Learn More:
HPO ID
80%-99% of people have these symptoms
Abnormal mitochondria in muscle tissue 0008316
Aphasia
Difficulty finding words
Losing words
Loss of words
[ more ] 		0002381
Aplasia/Hypoplasia of the cerebral white matter
Absent/small cerebral white matter
Absent/underdeveloped cerebral white matter
[ more ] 		0012429
Dementia
Dementia, progressive
Progressive dementia
[ more ] 		0000726
EEG abnormality 0002353
Increased serum lactate 0002151
Lactic acidosis
Increased lactate in body
0003128
Migraine
Intermittent migraine headaches
Migraine headache
Migraine headaches
[ more ] 		0002076
Muscle weakness
Muscular weakness
0001324
Ragged-red muscle fibers 0003200
Stroke-like episode 0002401
Widened cerebral subarachnoid space 0012766
30%-79% of people have these symptoms
Anxiety
Excessive, persistent worry and fear
0000739
Ataxia 0001251
Basal ganglia calcification 0002135
Bilateral tonic-clonic seizure
Grand mal seizures
0002069
Depressivity
Depression
0000716
Encephalopathy 0001298
Fluctuations in consciousness 0007159
Focal-onset seizure
Seizure affecting one half of brain
0007359
Gait disturbance
Abnormal gait
Abnormal walk
Impaired gait
[ more ] 		0001288
Hemiparesis
Weakness of one side of body
0001269
Impaired visuospatial constructive cognition 0010794
Increased CSF lactate 0002490
Increased CSF protein 0002922
Memory impairment
Forgetfulness
Memory loss
Memory problems
Poor memory
[ more ] 		0002354
Myoclonus 0001336
Myopathy
Muscle tissue disease
0003198
Recurrent paroxysmal headache 0002331
Sensorineural hearing impairment 0000407
Short attention span
Poor attention span
Problem paying attention
[ more ] 		0000736
Short stature
Decreased body height
Small stature
[ more ] 		0004322
Visual loss
Loss of vision
Vision loss
[ more ] 		0000572
Vomiting
Throwing up
0002013
5%-29% of people have these symptoms
Agenesis of corpus callosum 0001274
Anemia
Low number of red blood cells or hemoglobin
0001903
Bipolar affective disorder
Bipolar disorder
0007302
Cardiac conduction abnormality 0031546
Cerebral cortical atrophy
Decrease in size of the outer layer of the brain due to loss of brain cells
0002120
Concentric hypertrophic cardiomyopathy 0005157
Constipation 0002019
Diarrhea
Watery stool
0002014
Dilated cardiomyopathy
Stretched and thinned heart muscle
0001644
Distal peripheral sensory neuropathy 0007067
Elevated brain lactate level by MRS 0012707
Erythema 0010783
Exercise intolerance
Decreased ability to exercise
Inability to exercise
[ more ] 		0003546
Failure to thrive
Faltering weight
Weight faltering
[ more ] 		0001508
Fever 0001945
Focal segmental glomerulosclerosis 0000097
Global developmental delay 0001263
Hypertrichosis 0000998
Hypoplasia of the corpus callosum
Underdevelopment of part of brain called corpus callosum
0002079
Intestinal pseudo-obstruction 0004389
Mixed demyelinating and axonal polyneuropathy 0007327
Motor delay 0001270
Nephropathy 0000112
Optic atrophy 0000648
Peripheral axonal neuropathy 0003477
Personality changes
Personality change
0000751
Pigmentary retinopathy 0000580
Progressive external ophthalmoplegia 0000590
Proteinuria
High urine protein levels
Protein in urine
[ more ] 		0000093
Proximal tubulopathy 0000114
Psychotic mentation 0001345
Pulmonary arterial hypertension
Increased blood pressure in blood vessels of lungs
0002092
Recurrent pancreatitis
Recurring pancreas inflammation
0100027
Sensorimotor neuropathy
Nerve damage causing decreased feeling and movement
0007141
Stuttering
Stammering
0025268
Type I diabetes mellitus
Type 1 diabetes
Type I diabetes
[ more ] 		0100651
Type II diabetes mellitus
Noninsulin-dependent diabetes
Type 2 diabetes
Type II diabetes
[ more ] 		0005978
Vitiligo
Blotchy loss of skin color
0001045
Wolff-Parkinson-White syndrome 0001716
1%-4% of people have these symptoms
Hypogonadotropic hypogonadism 0000044
Hypoparathyroidism
Decreased parathyroid hormone secretion
0000829
Hypothyroidism
Underactive thyroid
0000821
Percent of people who have these symptoms is not available through HPO
Bilateral sensorineural hearing impairment 0008619
Cerebral visual impairment 0100704
Congestive heart failure
Cardiac failure
Cardiac failures
Heart failure
[ more ] 		0001635
Developmental cataract
Clouding of the lens of the eye at birth
0000519
Diabetes mellitus 0000819
Episodic vomiting 0002572
Growth abnormality
Abnormal growth
Growth issue
[ more ] 		0001507
Hemianopia 0012377
Hypertension 0000822
Left ventricular dysfunction 0005162
Left ventricular hypertrophy 0001712
Mitochondrial inheritance 0001427
Mitochondrial myopathy 0003737
Ophthalmoplegia
Eye muscle paralysis
0000602
Progressive sensorineural hearing impairment 0000408
Variable expressivity 0003828
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Last updated: 7/1/2020
MELAS is caused by mutations in mitochondrial DNA (mtDNA) and is therefore transmitted by maternal inheritance (also called mitochondrial inheritance).[2] This type of inheritance applies to all conditions caused by genes in mtDNA. Mitochondria are structures in each cell that turn molecules into energy, and each contain a small amount of DNA. Only egg cells (not sperm cells) contribute mitochondria to offspring, so only females can pass on mitochondrial mutations to their children.[3] Conditions resulting from mutations in mtDNA can appear in every generation of a family and can affect both males and females. In most cases, people with MELAS inherit an altered mitochondrial gene from their mother. Less commonly, the condition results from a new mutation in a mitochondrial gene and occurs in an individual with no history of MELAS in the family.[3]
Last updated: 12/4/2013

Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.
  • Orphanet lists international laboratories offering diagnostic testing for this condition.

If you need medical advice, you can look for doctors or other healthcare professionals who have experience with this disease. You may find these specialists through advocacy organizations, clinical trials, or articles published in medical journals. You may also want to contact a university or tertiary medical center in your area, because these centers tend to see more complex cases and have the latest technology and treatments.

If you can’t find a specialist in your local area, try contacting national or international specialists. They may be able to refer you to someone they know through conferences or research efforts. Some specialists may be willing to consult with you or your local doctors over the phone or by email if you can't travel to them for care.

You can find more tips in our guide, How to Find a Disease Specialist. We also encourage you to explore the rest of this page to find resources that can help you find specialists.

Healthcare Resources

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Clinical Research Resources

  • Orphanet lists European clinical trials, research studies, and patient registries enrolling people with this condition. 
  • The North American Mitochondrial Disease Consortium (NAMDC) is a team of doctors, nurses, research coordinators, and research labs throughout the U.S., working together to improve the lives of people with this condition through research.

Patient Registry

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

  • Genetics Home Reference (GHR) contains information on Mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes. This website is maintained by the National Library of Medicine.
  • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

In-Depth Information

  • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
  • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes. Click on the link to view a sample search on this topic.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know. Submit a new question

  • My brother was diagnosed with MELAS several years ago. His wife informed me that his doctor said that all 3 of us children inherited the gene from our mother. His diagnosis was confirmed after viewing our mother's autopsy reports. How probable is it that myself or our other brother will be affected by this disease? See answer

  • Is there a link between mitochondrial encephalomyopathy lactic acidosis and stroke-like episodes (MELAS) and a person who is not really strong? See answer


  1. Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes. Genetics Home Reference. November 2006; http://ghr.nlm.nih.gov/condition/mitochondrial-encephalomyopathy-lactic-acidosis-and-stroke-like-episodes. Accessed 10/17/2011.
  2. Salvatore DiMauro and Michio Hirano. MELAS. GeneReviews. November 21, 2013; http://www.ncbi.nlm.nih.gov/books/NBK1233/. Accessed 12/4/2013.
  3. Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes. Genetics Home Reference. November 2006; http://ghr.nlm.nih.gov/condition/mitochondrial-encephalomyopathy-lactic-acidosis-and-stroke-like-episodes. Accessed 12/4/2013.