Ataxia with vitamin E deficiency (AVED) is a rare inherited neurodegenerative disorder characterized by impaired ability to coordinate voluntary movements (ataxia) and disease of the peripheral nervous system (peripheral neuropathy). AVED is a progressive disorder that can affect many different systems of the body (multisystem disorder). Specific symptoms vary from case to case. In addition to neurological symptoms, affected individuals may experience eye abnormalities, disorders affecting the heart muscles (cardiomyopathy), and abnormal curvature of the spine (scoliosis). AVED is extremely similar to a more common disorder known as Friedreich’s ataxia. AVED is inherited as an autosomal recessive trait.
Vitamin E deficiency often occurs secondary to disorders that impair the absorption of vitamin E from fat including liver disorders, disorders of fat metabolism, and disorders of bile secretion. These disorders include cholestasis (a syndrome of various causes characterized by impaired bile secretion); cystic fibrosis (primarily a lung disorder that may also affect bile secretion); primary biliary cirrhosis (a liver disorder that results in cholestasis); and abetalipoproteinemia (a digestive disorder characterized by fat malabsorption). Premature infants may have a low vitamin E reserve because only small amounts of vitamin E cross the placenta, and therefore they may become deficient if fed a formula high in unsaturated fats and low in vitamin E. In rare cases, vitamin E deficiency may be caused by a poor diet. (For more information on the above disorders, choose the specific disorder name your search term in the Rare Disease Database.)
Symptoms
AVED affects the central nervous system resulting in peripheral neuropathy and ataxia. Peripheral neuropathy is a general term that denotes a disorder of the peripheral nervous system. The peripheral nervous system consists of all the motor and sensory nerves that connect the brain and spinal cord to the rest of the body (i.e., the nerves outside the central nervous system). Individuals with AVED develop progressive weakness of the legs, which may appear as a staggering, lurching way of walking (gait) or trembling when an affected individual is standing still. Ataxia is defined as a failure of muscle coordination that generally results in an unsteady gait. Without treatment, AVED may progress to cause significant difficulties walking and, potentially over the course of many years, can result in an affected individual becoming wheelchair bound.
Additional neurological findings include partial loss of the sense of touch or sensitivity to pain and temperature may also occur. With time, reflexes in the legs may slow or be absent (areflexia), and an abnormally high-arched foot (pes cavus) may develop with overextension (hyperextension) of the big toe. Involvement of the throat muscles may lead to impaired swallowing and choking and may cause difficulty in eating. Slurred speech (dysarthria) may also be present. Some affected individuals may develop a tremor or shaking of the head (titubation). Intellect and emotions are rarely affected.
In addition to neurological symptoms, individuals with AVED may develop symptoms affecting other systems of the body including eye abnormalities such as retinitis pigmentosa (RP), which is one name for a large group of vision disorders that cause progressive degeneration of the membrane lining the eyes (retina) resulting in visual impairment. Some affected individuals may have yellow “fatty” deposits (xanthelasmata) in the retina.
Clinical features
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Progressive ataxia
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Clumsiness of the hands
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Loss of proprioception (especially distal joint position and vibration sense)
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Areflexia
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Dysdiadochokinesia
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Positive Romberg sign
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Head titubation
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Decreased visual acuity
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Positive Babinski sign
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Macular atrophy, retinitis pigmentosa
Affected individuals may also develop lateral or sideways curvature of the spine (scoliosis), degenerative changes of the heart muscle (cardiomyopathy), or “fatty” deposits (xanthomas) affecting the Achilles tendon. Some individuals with AVED may experience a form of dystonia. Dystonia is the name for a group of movement disorders that is generally characterized by involuntary muscle contractions that force the body into abnormal, sometimes painful, movements and positions (postures).
Causes
AVED is inherited as an autosomal recessive trait. Genetic diseases are determined by two genes; one received from the father and one from the mother.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%.
Researchers have determined that AVED results from mutations of a gene on the long arm (q) of chromosome 8 (8q13.1-q13.3). The gene regulates production of a protein (alpha-tocopherol transfer protein) that binds vitamin E into fatty proteins (very-low-density lipoprotein or VLDL) produced and secreted by the liver. Individuals with AVED have an impaired ability to bind vitamin E into VLDL, which results in vitamin E deficiency in certain tissues.
The symptoms of AVED occur because of a deficiency of vitamin E, a fat-soluble vitamin that the body needs in very small amounts. It is stored in the body’s fat. Therefore, it is not necessary to consume vitamin E daily, as long as adequate amounts are stored in the body from a well balanced diet. Vitamin E is found in various foods including vegetable oils, wheat germ, whole-grain cereals, egg yolk, and liver. The liver stores the vitamin E-containing fat. Bile breaks down dietary fat in the small intestine so that vitamins can be absorbed. Vitamin E is an antioxidant, a substance used by the body to protect cells from free radicals, which are atoms that are normal by-products of metabolism. Free radicals damage the cells of the body.
Diagnosis
A diagnosis of AVED is made based upon a thorough clinical evaluation, a detailed patient history and a variety of tests and characteristic findings (e.g. low levels of vitamin E with normal levels of lipoproteins and lipids and no evidence of fat malabsorption).
Histopathology findings
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Spinal sensory demyelination with neuronal atrophy and axonal spheroids
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Dying back-type degeneration of the posterior columns
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Neuronal lipofuscin accumulation in the third cortical layer of the cerebral cortex, thalamus, lateral geniculate body, spinal horns, and posterior root ganglia
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Fiber type grouping of the peroneus brevis muscle
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Mild loss of Purkinje cells
Laboratory findings
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Normal lipid and lipoprotein profile
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Very low plasma vitamin E (α-tocopherol) concentrationNote: (1) There is no universal normal range of plasma vitamin E concentration, as it depends on the test method and varies among laboratories. In Finckh et al [1995], the normal range lies between 9.0 and 29.8 µmol/L (mean ± 2 SD). In El Euch-Fayache et al [2014] the normal range is given as 16.3-34.9 µmol/L, while individuals with AVED had vitamin E levels between 0.00 and 3.76 µmol/L (mean 0.95 µmol/L, SD 1.79 µmol/L; n=132). In individuals with AVED, the plasma vitamin E concentration is generally lower than 4.0 µmol/L (<1.7 mg/L). (2) Because oxidation of α-tocopherol by air may invalidate test results, the following precautions should be taken:
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Centrifugation of the EDTA blood soon after venipuncture
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Quick separation of plasma from blood cells after centrifugation and subsequent flash freezing of the plasma in liquid nitrogen
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Filling the space above the plasma with an inert gas (e.g., argon or nitrogen)
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Protecting the sample from light by wrapping the container in aluminum foil, or using a black or light-shielded Eppendorf tube
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Shipment of the sample to the test laboratory in dry ice
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Electrophysiologic findings
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In a large study of 132 individuals with AVED from North Africa, 45 individuals were investigated neurophysiologically (e.g., median and peroneal nerve motor conduction velocity, compound muscle action potential, median and saphenous nerve sensory action potential, and sensory action potential) [El Euch-Fayache et al 2014].
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9% had normal findings.
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47% had mild neuropathy (at least 1 parameter 70%-100% of lower limit of normal [LLN]).
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27% had moderate neuropathy (at least 1 parameter 30%-70% of LLN).
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17% had severe neuropathy (at least 1 parameter <30% of LLN or no response).
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Neuropathy was either purely sensory (34%), purely motor (24%), or combined (42%).
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Somatosensory evoked potentials show increased central conduction time between the segment C1 (N13b) and the sensorimotor cortex (N20), increased latencies of the N20 (median nerve) and P40 (tibial nerve) waves. The P40 wave may be missing completely [Schuelke et al 1999].
Note: No electrophysiologic findings are specific to or diagnostic of AVED; even a severe neuropathy does not exclude AVED.
Neuroimaging
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Cerebellar atrophy; present in approximately half of reported individuals
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Small T2-weighted high-intensity spots in the periventricular region and the deep white matter [Usuki & Maruyama 2000]; inconsistent finding in some individuals
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Single-gene testing. Sequence analysis of TTPA is performed first and followed by gene-targeted deletion/duplication analysis if only one or no pathogenic variant is found. Targeted analysis for TTPA pathogenic variant c.744delA can be performed first in individuals of Mediterranean or North African ancestry.
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A multigene panel that includes TTPA and other genes of interest may also be considered. Note: (1) The genes included and sensitivity of multigene panels vary by laboratory and are likely to change over time. (2) Some multigene panels may include genes not associated with the condition discussed in this GeneReview; thus, clinicians need to determine which multigene panel is most likely to identify the genetic cause of the condition while limiting the identification of variants of uncertain significance and pathogenic variants in genes that do not explain the underlying phenotype. (3) In some laboratories, panel options may include a custom laboratory-designed panel and/or custom phenotype-focused exome analysis that includes genes specified by the clinician. (4) Methods used in a panel may include sequence analysis, deletion/duplication analysis, and/or other non-sequencing-based tests.For an introduction to multigene panels click here..
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More comprehensive genomic testing (when available) including exome sequencing and genome sequencing may be considered if serial single-gene testing (and/or use of a multigene panel) fails to confirm a diagnosis in an individual with features of AVED. Such testing may provide or suggest a diagnosis not previously considered (e.g., mutation of a different gene or genes that results in a similar clinical presentation).
Treatment
Individuals with AVED are treated with vitamin E supplementation. Vitamin E treatment has often halted the progression of the disorder and, in some cases, improved existing neurological symptoms.
Genetic counseling may be of benefit for affected individuals and their families. Other treatment is symptomatic and supportive.
References
Ataxia Telangiectasia
