MERRF syndrome
Encyclopedia
MERRF syndrome is a mitochondrial disease
. It is extremely rare, with an estimated prevalence of 1/400,000 in Europe
, and has varying degrees of expressivity
owing to heteroplasmy
.
Many genes are involved. These include:
Mitochondrial disease
Mitochondrial diseases are a group of disorders caused by dysfunctional mitochondria, the organelles that are the "powerhouses" of the cell. Mitochondria are found in every cell of the human body except red blood cells...
. It is extremely rare, with an estimated prevalence of 1/400,000 in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, and has varying degrees of expressivity
Expressivity
Expressivity is a term used in genetics to refer to variations in a phenotype among individuals carrying a particular genotype. The term can be used to characterize qualitatively or quantitatively the extent of phenotypic variation given a particular genotype. The term is analogous to the...
owing to heteroplasmy
Heteroplasmy
Heteroplasmy is the presence of a mixture of more than one type of an organellar genome within a cell or individual...
Presentation
It involves the following characteristics:- progressive myoclonic epilepsyProgressive myoclonic epilepsyProgressive myoclonic epilepsy is a rare epilepsy syndrome caused by a variety of genetic disorders. It consists of both myoclonic seizures and tonic-clonic seizures together with progressive neurological decline....
- "Ragged Red Fibers" - clumps of diseased mitochondria accumulate in the subsarcolemmal region of the muscle fiber and appear as "Ragged Red Fibers" when muscle is stained with modified Gömöri trichrome stainGomori trichrome stainGömöri trichrome stain is a stain used on muscle tissue.It can be used to test for certain forms of mitochondrial myopathy.It is named for George Gömöri, who developed it in 1950.-External links:...
- short statureShort statureShort stature refers to a height of a human being which is below expected. Shortness is a vague term without a precise definition and with significant relativity to context...
- hearing loss
- lactic acidosisLactic acidosisLactic acidosis is a physiological condition characterized by low pH in body tissues and blood accompanied by the buildup of lactate especially D-lactate, and is considered a distinct form of metabolic acidosis. The condition typically occurs when cells receive too little oxygen , for example...
- exercise intoleranceExercise intoleranceExercise intolerance is a condition where the patient is unable to do physical exercise at the level or for the duration that would be expected of someone in his or her general physical condition, or experiences unusually severe post-exercise pain, fatigue, or other negative effects...
- poor night visionNight visionNight vision is the ability to see in low light conditions. Whether by biological or technological means, night vision is made possible by a combination of two approaches: sufficient spectral range, and sufficient intensity range...
Causes
The MERRF syndrome is caused by a maternally-inherited mutation at position 8344 in the mitochondrial genome in over 80% of cases. This point mutation disrupts the mitochondrial gene for tRNA-Lys and so disrupts synthesis of proteins essential for oxidative phosphorylationOxidative phosphorylation
Oxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate . Although the many forms of life on earth use a range of different nutrients, almost all aerobic organisms carry out oxidative phosphorylation to produce ATP,...
.
Many genes are involved. These include:
- MT-TKMT-TKMitochondrially encoded tRNA lysine also known as MT-TK is a transfer RNA which in humans is encoded by the mitochondrial MT-TK gene.- Function :...
- MT-TL1MT-TL1Mitochondrially encoded tRNA leucine 1 also known as MT-TL1 is a transfer RNA which in humans is encoded by the mitochondrial MT-TL1 gene.-Function:...
- MT-THMT-THMitochondrially encoded tRNA histidine, also known as MT-TH, is a transfer RNA which, in humans, is encoded by the mitochondrial MT-TH gene.-Function:...
- MT-TS1MT-TS1Mitochondrially encoded tRNA serine 1 also known as MT-TS1 is a transfer RNA which in humans is encoded by the mitochondrial MT-TS1 gene....
- MT-TS2MT-TS2Mitochondrially encoded tRNA serine 2 also known as MT-TS2 is a transfer RNA which in humans is encoded by the mitochondrial MT-TS2 gene....
- MT-TFMT-TFMitochondrially encoded tRNA phenylalanine also known as MT-TF is a transfer RNA which in humans is encoded by the mitochondrial MT-TF gene....