MELAS syndrome

Mitochondrial myopathy, encephalomyopathy, lactic acidosis, and stroke-like episodes
Basal ganglia calcification, cerebellar atrophy, increased lactate; a CT image of a person diagnosed with MELAS
Classification and external resources
Specialty neurology
ICD-10 G31.8
ICD-9-CM 277.87
OMIM 540000
DiseasesDB 8254
eMedicine ped/1406
MeSH D017241

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes – abbreviated to MELAS – is one of the family of mitochondrial cytopathies, which also include MERRF, and Leber's hereditary optic neuropathy. It was first characterized under this name in 1984.[1] A feature of these diseases is that they are caused by defects in the mitochondrial genome which is inherited purely from the female parent.[2] However, it is important to know that some of the proteins essential to normal mitochondrial function are produced by the nuclear genome, and are subsequently transported to the mitochondria for use. As such, mutations in these proteins can result in mitochondrial disorders, but can be inherited from both male and female parent in the typical fashion. The disease can manifest in both sexes.

Signs 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.[3] 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). The stroke-like episodes can be mis-diagnosed as epilepsy by a doctor not aware of the MELAS condition.

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, loss of bowel control, 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, epilepsy, and hormonal imbalances.

The presentation of some cases is similar to that of Kearns-Sayre syndrome.[4]

Genetics

Muscle biopsy of a person diagnosed with MELAS but carrying no known mutation. (a) Modified Gomori trichrome stain showing several ragged red fibers (arrowhead). (b) Cytochrome c oxidase stain showing Type-1 lightly stained and Type II fibers, darker fibers, and a few fibers with abnormal collections of mitochondria (arrowhead). Note cytochrome c oxidase negative fibers as usually seen in mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS). (c) Succinate dehydrogenase staining showing a few ragged blue fibers and intense staining in the mitochondria of the blood vessels (arrow). (d) Electron microscopy showing abnormal collection of mitochondria with paracrystalline inclusions (arrowhead), osmiophilic inclusions (large arrowhead) and mitochondrial vacuoles (small arrowhead).[5]

MELAS is caused by mutations in the genes in mitochondrial DNA.

NADH dehydrogenase

Some of the genes (MT-ND1, MT-ND5) affected in MELAS encode proteins that are part of NADH dehydrogenase (also called complex I) in mitochondria, that helps convert oxygen and simple sugars to energy.[6]

Transfer RNAs

Other genes (MT-TH, MT-TL1, and MT-TV) encode mitochondrial specific transfer RNAs (tRNAs).

Mutations in MT-TL1 cause more than 80 percent of all cases of MELAS. They 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.

Inheritance

This condition is inherited in a mitochondrial pattern, which is also known as maternal inheritance and heteroplasmy. 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.

Treatment/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. Enzymes, amino acids, antioxidants and vitamins have been used, but there have been no consistent successes reported.

Although there have been no controlled trials on long-term benefits of dietary manipulations, the following supplements have shown promise and given hope to MELAS patients.

Epidemiology

The exact incidence of MELAS is unknown.[11] It is one of the more common conditions in a group known as mitochondrial diseases.[11] Together, mitochondrial diseases occur in about 1 in 4,000 people.[11]

References

  1. ↑ Pavlakis SG, Phillips PC, DiMauro S, De Vivo DC, Rowland LP (1984). "Mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes: a distinctive clinical syndrome". Ann Neurol. 16 (4): 481–8. PMID 6093682. doi:10.1002/ana.410160409.
  2. ↑ Hirano M, Pavlakis SG (1994). "Mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS): current concepts". J Child Neurol. 9 (1): 4–13. PMID 8151079. doi:10.1177/088307389400900102.
  3. ↑ MELAS syndrome at NLM Genetics Home Reference
  4. ↑ Hirano M, Ricci E, Koenigsberger MR, Defendini R, Pavlakis SG, DeVivo DC, DiMauro S, Rowland LP (1992). "Melas: an original case and clinical criteria for diagnosis". Neuromuscul Disord. 2 (2): 125–35. PMID 1422200. doi:10.1016/0960-8966(92)90045-8.
  5. ↑ Abu-Amero KK, Al-Dhalaan H, Bohlega S, Hellani A, Taylor RW (2009). "A patient with typical clinical features of mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS) but without an obvious genetic cause: a case report". J Med Case Reports. 3: 77. PMC 2783076 Freely accessible. PMID 19946553. doi:10.1186/1752-1947-3-77.
  6. ↑ Tranchant, C.; Anheim, M. (2016). "Movement disorders in mitochondrial diseases". Revue Neurologique. ISSN 0035-3787. doi:10.1016/j.neurol.2016.07.003.
  7. ↑ Rodriguez MC, MacDonald JR, Mahoney DJ, Parise G, Beal MF, Tarnopolsky MA (2007). "Beneficial effects of creatine, CoQ10, and lipoic acid in mitochondrial disorders". Muscle Nerve. 35 (2): 235–42. PMID 17080429. doi:10.1002/mus.20688.
  8. ↑ Ogle RF, Christodoulou J, Fagan E, et al. (1997). "Mitochondrial myopathy with tRNA(Leu(UUR)) mutation and complex I deficiency responsive to riboflavin". J. Pediatr. 130 (1): 138–45. PMID 9003864. doi:10.1016/S0022-3476(97)70323-8.
  9. ↑ Koga Y, Akita Y, Nishioka J, et al. (2007). "MELAS and L-arginine therapy". Mitochondrion. 7 (1-2): 133–9. PMID 17276739. doi:10.1016/j.mito.2006.11.006.
  10. ↑ Hirata K, Akita Y, Povalko N, et al. (2007). "Effect of l-arginine on synaptosomal mitochondrial function". Brain Dev. 30 (4): 238–45. PMID 17889473. doi:10.1016/j.braindev.2007.08.007.
  11. 1 2 3 "MELAS". Genetics Home Reference. December 2013. Retrieved 11 April 2017. This article incorporates text from this source, which is in the public domain.
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