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Mitochondrial DNA depletion syndrome 4b(MTDPS4B)

MedGen UID:
462264
Concept ID:
C3150914
Disease or Syndrome
Synonyms: Mitochondrial DNA depletion syndrome 4B, MNGIE type; Mitochondrial Neurogastrointestinal Encephalopathy Disease, POLG-Related; MNGIE, POLG-RELATED
 
Gene (location): POLG (15q26.1)
 
Monarch Initiative: MONDO:0013350
OMIM®: 613662

Disease characteristics

Excerpted from the GeneReview: POLG-Related Disorders
POLG-related disorders comprise a continuum of overlapping phenotypes that were clinically defined long before their molecular basis was known. Most affected individuals have some, but not all, of the features of a given phenotype; nonetheless, the following nomenclature can assist the clinician in diagnosis and management. Onset of the POLG-related disorders ranges from infancy to late adulthood. Alpers-Huttenlocher syndrome (AHS), one of the most severe phenotypes, is characterized by childhood-onset progressive and ultimately severe encephalopathy with intractable epilepsy and hepatic failure. Childhood myocerebrohepatopathy spectrum (MCHS) presents between the first few months of life and about age three years with developmental delay or dementia, lactic acidosis, and a myopathy with failure to thrive. Other findings can include liver failure, renal tubular acidosis, pancreatitis, cyclic vomiting, and hearing loss. Myoclonic epilepsy myopathy sensory ataxia (MEMSA) now describes the spectrum of disorders with epilepsy, myopathy, and ataxia without ophthalmoplegia. MEMSA now includes the disorders previously described as spinocerebellar ataxia with epilepsy (SCAE). The ataxia neuropathy spectrum (ANS) includes the phenotypes previously referred to as mitochondrial recessive ataxia syndrome (MIRAS) and sensory ataxia neuropathy dysarthria and ophthalmoplegia (SANDO). About 90% of persons in the ANS have ataxia and neuropathy as core features. Approximately two thirds develop seizures and almost one half develop ophthalmoplegia; clinical myopathy is rare. Autosomal recessive progressive external ophthalmoplegia (arPEO) is characterized by progressive weakness of the extraocular eye muscles resulting in ptosis and ophthalmoparesis (or paresis of the extraocular muscles) without associated systemic involvement; however, caution is advised because many individuals with apparently isolated arPEO at the onset develop other manifestations of POLG-related disorders over years or decades. Of note, in the ANS spectrum the neuropathy commonly precedes the onset of PEO by years to decades. Autosomal dominant progressive external ophthalmoplegia (adPEO) typically includes a generalized myopathy and often variable degrees of sensorineural hearing loss, axonal neuropathy, ataxia, depression, parkinsonism, hypogonadism, and cataracts (in what has been called "chronic progressive external ophthalmoplegia plus," or "CPEO+"). [from GeneReviews]
Authors:
Bruce H Cohen  |  Patrick F Chinnery  |  William C Copeland   view full author information

Additional descriptions

From OMIM
Mitochondrial DNA depletion syndrome-4B (MTDPS4B) is an autosomal recessive progressive multisystem disorder clinically characterized by chronic gastrointestinal dysmotility and pseudoobstruction, cachexia, progressive external ophthalmoplegia (PEO), axonal sensory ataxic neuropathy, and muscle weakness (van Goethem et al., 2003). For a discussion of genetic heterogeneity of autosomal recessive mtDNA depletion syndromes, see MTDPS1 (603041).  http://www.omim.org/entry/613662
From MedlinePlus Genetics
MNGIE disease is also characterized by abnormalities of the nervous system, although these tend to be milder than the gastrointestinal problems. Affected individuals experience tingling, numbness, and weakness in their limbs (peripheral neuropathy), particularly in the hands and feet. Additional neurological signs and symptoms can include droopy eyelids (ptosis), weakness of the muscles that control eye movement (ophthalmoplegia), and hearing loss. Leukoencephalopathy, which is the deterioration of a type of brain tissue known as white matter, is a hallmark of MNGIE disease. These changes in the brain can be seen with magnetic resonance imaging (MRI), though they usually do not cause symptoms in people with this disorder.

Almost all people with MNGIE disease have a condition known as gastrointestinal dysmotility, in which the muscles and nerves of the digestive system do not move food through the digestive tract efficiently. The resulting digestive problems include feelings of fullness (satiety) after eating only a small amount, trouble swallowing (dysphagia), nausea and vomiting after eating, episodes of abdominal pain, diarrhea, and intestinal blockage. These gastrointestinal problems lead to extreme weight loss and reduced muscle mass (cachexia).

Mitochondrial neurogastrointestinal encephalopathy (MNGIE) disease is a condition that affects several parts of the body, particularly the digestive system and nervous system. The major features of MNGIE disease can appear anytime from infancy to adulthood, but signs and symptoms most often begin by age 20. The medical problems associated with this disorder worsen over time.  https://medlineplus.gov/genetics/condition/mitochondrial-neurogastrointestinal-encephalopathy-disease

Clinical features

From HPO
Abdominal pain
MedGen UID:
7803
Concept ID:
C0000737
Sign or Symptom
An unpleasant sensation characterized by physical discomfort (such as pricking, throbbing, or aching) and perceived to originate in the abdomen.
Cachexia
MedGen UID:
2773
Concept ID:
C0006625
Sign or Symptom
Severe weight loss, wasting of muscle, loss of appetite, and general debility related to a chronic disease.
Weight loss
MedGen UID:
853198
Concept ID:
C1262477
Finding
Reduction of total body weight.
Slender build
MedGen UID:
376828
Concept ID:
C1850573
Finding
Asthenic habitus refers to a slender build with long limbs, an angular profile, and prominent muscles or bones.
Abdominal distention
MedGen UID:
34
Concept ID:
C0000731
Finding
Distention of the abdomen.
Constipation
MedGen UID:
1101
Concept ID:
C0009806
Sign or Symptom
Infrequent or difficult evacuation of feces.
Intestinal pseudo-obstruction
MedGen UID:
5864
Concept ID:
C0021847
Disease or Syndrome
A functional rather than mechanical obstruction of the intestines, associated with manifestations that resemble those caused by an intestinal obstruction, including distension, abdominal pain, nausea, vomiting, constipation or diarrhea, in an individual in whom a mechanical blockage has been excluded.
Malnutrition
MedGen UID:
56429
Concept ID:
C0162429
Disease or Syndrome
A deficiency in the intake of energy and nutrients.
Gastrointestinal dysmotility
MedGen UID:
324638
Concept ID:
C1836923
Finding
Abnormal intestinal contractions, such as spasms and intestinal paralysis, related to the loss of the ability of the gut to coordinate muscular activity because of endogenous or exogenous causes.
Malabsorption
MedGen UID:
811453
Concept ID:
C3714745
Finding
Impaired ability to absorb one or more nutrients from the intestine.
Hearing impairment
MedGen UID:
235586
Concept ID:
C1384666
Disease or Syndrome
A decreased magnitude of the sensory perception of sound.
Cerebellar ataxia
MedGen UID:
849
Concept ID:
C0007758
Disease or Syndrome
Cerebellar ataxia refers to ataxia due to dysfunction of the cerebellum. This causes a variety of elementary neurological deficits including asynergy (lack of coordination between muscles, limbs and joints), dysmetria (lack of ability to judge distances that can lead to under- or overshoot in grasping movements), and dysdiadochokinesia (inability to perform rapid movements requiring antagonizing muscle groups to be switched on and off repeatedly).
Seizure
MedGen UID:
20693
Concept ID:
C0036572
Sign or Symptom
A seizure is an intermittent abnormality of nervous system physiology characterised by a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain.
Global developmental delay
MedGen UID:
107838
Concept ID:
C0557874
Finding
A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.
Abnormal cerebral white matter morphology
MedGen UID:
181756
Concept ID:
C0948163
Pathologic Function
An abnormality of the cerebral white matter.
Sensory ataxic neuropathy
MedGen UID:
336060
Concept ID:
C1843859
Finding
Hypotonia
MedGen UID:
10133
Concept ID:
C0026827
Finding
Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.
Muscle weakness
MedGen UID:
57735
Concept ID:
C0151786
Finding
Reduced strength of muscles.
Inborn mitochondrial myopathy
MedGen UID:
56484
Concept ID:
C0162670
Disease or Syndrome
A type of myopathy associated with mitochondrial disease and characterized by findings on biopsy such as ragged red muscle fibers.
Generalized muscle weakness
MedGen UID:
155433
Concept ID:
C0746674
Sign or Symptom
Generalized weakness or decreased strength of the muscles, affecting both distal and proximal musculature.
Generalized hypotonia
MedGen UID:
346841
Concept ID:
C1858120
Finding
Generalized muscular hypotonia (abnormally low muscle tone).
Ragged-red muscle fibers
MedGen UID:
477048
Concept ID:
C3275417
Finding
An abnormal appearance of muscle fibers observed on muscle biopsy. Ragged red fibers can be visualized with Gomori trichrome staining as irregular and intensely red subsarcolemmal zones, whereas the normal myofibrils are green. The margins of affect fibers appear red and ragged. The ragged-red is due to the accumulation of abnormal mitochondria below the plasma membrane of the muscle fiber, leading to the appearance of a red rim and speckled sarcoplasm.
Multiple mitochondrial DNA deletions
MedGen UID:
479006
Concept ID:
C3277376
Finding
The presence of multiple deletions of mitochondrial DNA (mtDNA).
Depletion of mitochondrial DNA in muscle tissue
MedGen UID:
867163
Concept ID:
C4021521
Finding
Cytochrome C oxidase-negative muscle fibers
MedGen UID:
867360
Concept ID:
C4021724
Finding
An abnormally reduced activity of the enzyme cytochrome C oxidase in muscle tissue.
Progressive external ophthalmoplegia
MedGen UID:
102439
Concept ID:
C0162674
Disease or Syndrome
Progressive external ophthalmoplegia is a condition characterized by weakness of the eye muscles. The condition typically appears in adults between ages 18 and 40 and slowly worsens over time. The first sign of progressive external ophthalmoplegia is typically drooping eyelids (ptosis), which can affect one or both eyelids. As ptosis worsens, affected individuals may use the forehead muscles to try to lift the eyelids, or they may lift up their chin in order to see. Another characteristic feature of progressive external ophthalmoplegia is weakness or paralysis of the muscles that move the eye (ophthalmoplegia). Affected individuals have to turn their head to see in different directions, especially as the ophthalmoplegia worsens. People with progressive external ophthalmoplegia may also have general weakness of the muscles used for movement (myopathy), particularly those in the neck, arms, or legs. The weakness may be especially noticeable during exercise (exercise intolerance). Muscle weakness may also cause difficulty swallowing (dysphagia).\n\nProgressive external ophthalmoplegia is part of a spectrum of disorders with overlapping signs and symptoms. Similar disorders include ataxia neuropathy spectrum and Kearns-Sayre syndrome. Like progressive external ophthalmoplegia, the other conditions in this spectrum can involve weakness of the eye muscles. However, these conditions have many additional features not shared by most people with progressive external ophthalmoplegia.\n\nWhen the muscle cells of affected individuals are stained and viewed under a microscope, these cells usually appear abnormal. These abnormal muscle cells contain an excess of cell structures called mitochondria and are known as ragged-red fibers.\n\nAlthough muscle weakness is the primary symptom of progressive external ophthalmoplegia, this condition can be accompanied by other signs and symptoms. In these instances, the condition is referred to as progressive external ophthalmoplegia plus (PEO+). Additional signs and symptoms can include hearing loss caused by nerve damage in the inner ear (sensorineural hearing loss), weakness and loss of sensation in the limbs due to nerve damage (neuropathy), impaired muscle coordination (ataxia), a pattern of movement abnormalities known as parkinsonism, and depression.
Decreased activity of mitochondrial complex I
MedGen UID:
393796
Concept ID:
C2677650
Finding
A reduction in the activity of the mitochondrial respiratory chain complex I, which is part of the electron transport chain in mitochondria.
Decreased activity of mitochondrial complex IV
MedGen UID:
866520
Concept ID:
C4020800
Finding
A reduction in the activity of the mitochondrial respiratory chain complex IV, which is part of the electron transport chain in mitochondria.

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