Neuroacanthocytosis is a general term for a group of rare progressive disorders characterized by the association of misshapen, spiny red blood cells (acanthocytosis) and neurological abnormalities, especially movement disorders. Chorea, which is characterized by rapid, involuntary, purposeless movements, especially of the face, feet and hands, is the most common movement disorder associated with neuroacanthocytosis. Additional symptoms often develop including progressive cognitive impairment, muscle weakness, seizures and behavioral or personality changes. The onset, severity and specific physical findings vary depending upon the specific type of neuroacanthocytosis present. Neuroacanthocytosis syndromes typically progress to cause serious, disabling and sometimes life-threatening complications (and are usually fatal). These disorders are inherited although the mode of transmission can vary. There is disagreement in the medical literature about what disorders should be classified as forms of neuroacanthocytosis. Four distinct disorders are usually classified as the "core" neuroacanthocytosis syndromes - chorea-acanthocytosis, McLeod syndrome, Huntington's disease-like 2 and pantothenate kinase-associated neurodegeneration (PKAN). Some medical sources also include abetalipoproteinemia and hypobetalipoproteinemia types I and II as forms of neuroacanthocytosis. This report concentrates only on the four "core" disorders of neuroacanthocytosis. NORD has a separate report on abetalipoproteinemia.
The symptoms and severity of neuroacanthocytosis can vary from one person to another, even among individuals with the same subtype or among individuals within the same family. It is important to note that affected individuals may not have all of the symptoms discussed below. Affected individuals should talk to their physician and medical team about their specific case, associated symptoms and overall prognosis.
The age of onset and progression of these disorders also varies. Chorea-acanthocytosis and McLeod syndrome progress slowly over many years or decades during adulthood. In many cases, PKAN presents in childhood and rapidly progresses within 10 years. These disorders can all potentially progress to cause life-threatening complications.
All of these disorders share certain findings including abnormal involuntary movements, cognitive deterioration and acanthocytosis. The most common movement disorder associated with neuroacanthocytosis is chorea, which is characterized by rapid, involuntary, purposeless movements, especially of the face, arms and legs.
Although the neuroacanthocytosis syndromes are marked by the association of acanthocytosis and movement disorders, acanthocytosis does not occur in all cases (variable finding). Specifically, acanthocytosis refers to the presence of abnormally-shaped red blood cells called acanthocytes. Red blood cells are formed in the bone marrow and released into the bloodstream where they travel throughout the body delivering oxygen to tissue. Normally, red blood cells have a life span of approximately 120 days before they are removed by the spleen. Acanthocytes are abnormal red blood cells that have thorny or spiny projections of varying lengths protruding from the surface of the cell. They are also known as “spur” cells. Most adults normally have a small percentage of these unique red blood cells. When individuals have abnormally high levels of acanthocytes, it often indicates the presence of an underlying disorder. Specific symptoms that occur in association with acanthocytosis are related to the underlying cause of the condition.
Acanthocytosis occurs most often with chorea-acanthocytosis and McLeod syndrome. It is seen less frequently in individuals with Huntington’s disease-like 2 or PKAN.
Chorea affecting the arms and legs is the most common finding of chorea-acanthocytosis. Affected individuals may exhibit abnormal movements of the arms and legs, shoulder shrugs and pelvic thrusts. The abnormal movements of the arms and legs are often compared to dancing or piano playing. These movements may also cause an abnormal manner of walking (gait) characterized by lurching and involuntary knee flexion. In most cases, chorea begins in adulthood and is slowly progressive. In some cases, chorea-acanthocytosis can eventually progress so that individuals require a wheelchair or become bedridden.
In addition to chorea, individuals with chorea-acanthocytosis also exhibit dystonia. Dystonia is a general term for a group of neurological conditions characterized by involuntary muscle contractions that force certain part(s) of the body into abnormal, movements and positions (postures). Dystonia affecting the mouth and face is common in chorea-acanthocytosis.
Dystonia and chorea affecting the muscles of the face and tongue can cause a variety of symptoms. These symptoms may be referred to as orofacial and lingual dyskinesia and include protrusion of the tongue, grimacing, and abnormal jaw movements. Chronic teeth grinding, involuntary belching, drooling and spitting have also been reported. Many individuals will habitually bite the lip and tongue, potentially causing mutilation. Some affected individuals may eventually develop difficulty swallowing (dysphagia). The various orofacial and lingual dyskinesias can cause significant feeding problems and unintended weight loss. Difficulties with speech and communication, usually due to problems with the muscles that enable speech (dysarthria), are also common findings. Vocal tics such as grunting or involuntary speaking can also occur. Slurred speech is common and eventually chorea-acanthocytosis can progress to limit speech to grunting or whispering. In some cases, affected individuals may eventually become mute.
Less often, individuals with chorea-acanthocytosis develop parkinsonism, which is characterized by symptoms that resemble Parkinson’s disease including slow, stiff movements, tremors and low speech.
Other typical findings are nerve damage (peripheral neuropathy), resulting in absence of reflexes (areflexia) and sensory loss. Progressive wasting of muscle tissue (amyotrophy) and muscle weakness are often seen as well. Occasionally these are the first features to develop, and suggest a primary nerve or muscle disease. Seizures are seen in about 50 percent of people with this condition and can be a presenting sign.
A wide variety of personality or behavioral changes may occur in individuals with chorea-acanthocytosis including apathy, irritability, hyperactivity, depression, slowness of thought and emotional instability. Anxiety, paranoia, disinhibition, aggression, and self-neglect have also occurred. Some affected individuals develop obsessive-compulsive disorders such as chronic hair pulling (trichotillomania). Eventually, chorea-acanthocytosis may cause progressive memory loss and deterioration of intellectual abilities (dementia).
In the past, chorea-acanthocytosis was also known as Levine-Critchley syndrome. The family reported by Dr. Critchley has been genetically confirmed to have chorea-acanthocytosis, however, it is not known what the diagnosis was of the family reported by Dr. Levine, thus this term is imprecise. Sometimes, the term neuroacanthocytosis is used specifically to refer to chorea-acanthocytosis.
McLeod syndrome is a rare multisystem disorder characterized by various abnormalities, especially those affecting the central nervous system. The specific symptoms can vary greatly from one person to another. The disorder predominantly affects males, although in rare cases females have developed some symptoms of the disorder.
Affected individuals may experience chorea, especially affecting the arms and legs but also affecting the trunk, face and neck. Chorea is slowly progressive and can eventually affect the ability to walk. Unlike chorea-acanthocytosis, lip and tongue biting are not typically seen in McLeod syndrome. Dystonia and parkinsonism are also far less common in McLeod syndrome than in chorea-acanthocytosis.
Affected males may also have muscle weakness, muscle degeneration, and absence of deep tendon reflexes usually due to nerve damage. In some cases, seizures may occur and can be the presenting sign of the disorder.
Cognitive impairment has also been reported in approximately 50 percent of cases. Cognitive impairment can cause memory loss as well as difficulties learning or processing new information. Cognitive impairment can affect a person’s ability to manage everyday tasks and activities. The severity of cognitive impairment in McLeod syndrome can vary greatly even among members of the same family. It can range from slight problems with memory to dementia.
Psychiatric problems may occur in McLeod syndrome including apathy, disinhibition, irritability, anxiety, distractibility, and depression. Some affected individuals may develop obsessive-compulsive disorder. In some families, psychiatric problems may predominate (as oppose to movement abnormalities).
Affected individuals may also develop heart (cardiac) problems including abnormal electrical activity in the heart (arrhythmia) and dilated cardiomyopathy. Dilated cardiomyopathy is characterized by abnormal enlargement or widening (dilatation) of one or ventricles which results in a weakening of the heart’s pumping action, causing a limited ability to circulate blood to the lungs and the rest of the body which may result in fluid buildup in the heart, lung and various body tissues (congestive heart failure).
Additional symptoms may occur in McLeod syndrome including an enlarged liver and spleen (hepatosplenomegaly).
A characteristic finding associated with McLeod syndrome is absent expression of the Kx red blood cell antigen and weak expression of Kell blood group antigens. Antigens are substances that cause immune system to produce antibodies. The Kx antigen is normally found on the surface of erythrocytes (red blood cells). These characteristic findings are referred to as the McLeod blood group phenotype. Because of abnormalities affecting these antigens, individuals with McLeod syndrome may be susceptible to adverse reactions to blood transfusions with incompatible blood. The exact role these antigens play in the development of McLeod syndrome is not fully understood.
HUNTINGTON’S DISEASE-LIKE 2
Huntington’s disease-like 2 (HDL-2) is an autosomal dominant disorder remarkably like Huntington’s disease but characterized by a trinucleotide repeat expansion in a different gene. Onset typically occurs in the third-fourth decade, with involuntary movements and abnormalities of voluntary movements, as well as dementia.
Specific symptoms may include a variety of movement disorders including dystonia and chorea Affected individuals may also develop excessive or exaggerated response of certain reflexes (hyperreflexia), extreme slowness of voluntary movements (bradykinesia) and difficulty with speech and communication. Cognitive impairment is typical and can eventually progress to cause dementia.
Behavioral and psychiatric problems may also occur in Huntington’s disease-like 2 including depression, anxiety, irritability, and apathy. Some affected individuals may experience delusions or hallucinations.
PANTOTHENATE KINASE-ASSOCIATED NEURODEGENERATION (PKAN)
PKAN is a form of neurodegeneration with brain iron accumulation (NBIA). It is the largest subgroup of NBIA observed so far. The common feature among affected individuals is iron accumulation in the brain, along with a progressive movement disorder. Individuals can remain stable for long periods of time and then undergo intervals of rapid deterioration.
Common features include dystonia, an abnormality in muscle tone, muscular rigidity, and sudden involuntary muscle spasms (spasticity) that result in slow, stiff movements of the legs. These features can result in clumsiness, gait (walking) problems, difficulty controlling movement, and speech problems. Another common feature is degeneration of the retina (retinopathy), resulting in progressive night blindness and loss of peripheral (side) vision. In general, symptoms are progressive and become worse over time.
Atypical cases develop after the age of 20 and are characterized by dystonia, rigidity and gait abnormalities. The progression of the atypical cases is slower than in younger children and retinopathy does not occur. Speech abnormalities including dysarthria are common. Personality changes and progressive cognitive decline are also seen.
The four core disorders under the umbrella term neuroacanthocytosis are genetic disorders. They are caused by mutations in specific genes. The mode of inheritance and age of onset varies.
Chorea-acanthocytosis and PKAN are inherited as autosomal recessive traits. Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and 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 percent with each pregnancy. The risk to have a child who is a carrier like the parents is 50 percent 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 percent. The risk is the same for males and females.
Huntington’s disease-like 2 is inherited as an autosomal dominant trait. Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50 percent for each pregnancy regardless of the sex of the resulting child.
McLeod syndrome is inherited as an X-linked recessive trait. X-linked recessive genetic disorders are conditions caused by an abnormal gene on the X chromosome. Females have two X chromosomes but one of the X chromosomes is “turned off” and all of the genes on that chromosome are inactivated. Females who have a disease gene present on one of their X chromosomes are carriers for that disorder. Carrier females usually do not display symptoms of the disorder because it is usually the X chromosome with the abnormal gene that is “turned off”. A male has one X chromosome and if he inherits an X chromosome that contains a disease gene, he will develop the disease. Males with X-linked disorders pass the disease gene to all of their daughters, who will be carriers. A male cannot pass an X-linked gene to his sons because males always pass their Y chromosome instead of their X chromosome to male offspring. Female carriers of an X-linked disorder have a 25 percent chance with each pregnancy to have a carrier daughter like themselves, a 25 percent chance to have a non-carrier daughter, a 25 percent chance to have a son affected with the disease, and a 25 percent chance to have an unaffected son.
Chorea-acanthocytosis is caused by mutations of the VPS13A gene located on the long arm (q) of chromosome 9 (9q21). Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 9q21″ refers to band 21 on the long arm of chromosome 9. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
The VPS13A gene contains instructions for creating (encoding) a protein known as chorein. The exact role and function of chorein is not fully understood, but it may be involved in transporting cellular proteins.
McLeod syndrome is caused by mutations of the XK gene located on the X chromosome. The XK gene encodes the XK protein, which bears (expresses) the Kx red blood cell antigen. The exact function of the XK protein is not fully understood. This protein is believed to play a role in transport and possibly may assist substances to move into and out of cells. The XK protein is found in the brain, muscle and heart and on the surface of red blood cells.
Huntington’s disease-like 2 is caused by mutations of the junctophilin 3 (JPH3) gene located on the long arm (q) of chromosome 16 (16q24.3). The JPH3 gene encodes the protein JPH3, which is believed to play a role in certain membrane structures and in regulating calcium.
PKAN is caused by mutations of the pantothenate kinase 2 gene (PANK2) located on the short arm (p) on chromosome 20 (20p13-p12.3). The PANK2 gene encodes the PANK2 protein, which is active in the nerve cells in the brain.
Most individuals with a neuroacanthocytosis syndrome have progression degeneration of an area deep within the brain known as the basal ganglia, which is a cluster of nerve cells located near the base of the brain that processes information involved in involuntary movements, coordination and cognition. The exact roles that these proteins play in the development of neuroacanthocytosis syndromes are unknown. Nor is it known whether they are related in any way. Researchers are investigating how the missing or nonfunctioning proteins result in or contribute to damage in the brain that ultimately causes the symptoms of these disorders.
Chorea-acanthocytosis most often affects individuals between the ages of 20 and 40, although in rare cases, it can develop in individuals younger than 20 and older than 50. McLeod syndrome typically develops in males between the ages of 40-60. PKAN most often affects children under the age of 10, although in atypical cases onset is often after the age of 20. The age of onset of Huntington’s disease-like 2 is variable. The disorder has been reported only in a few families, all of whom are of African descent. Chorea-acanthocytosis, PKAN and Huntington’s disease-like 2 affect males and females in equal numbers. McLeod syndrome predominantly affects males, although in rare cases females have developed some symptoms of the disorder.
The exact incidence of neuroacanthocytosis is unknown. These disorders may go misdiagnosed or undiagnosed making it difficult to determine their true frequency in the general population.
A diagnosis of neuroacanthocytosis is made based upon identification of characteristic symptoms, a detailed patient history, a thorough clinical evaluation and a variety of specialized tests. Blood tests can reveal the presence of acanthocytes in the blood, although their absence does not exclude a diagnosis of neuroacanthocytosis. Imaging techniques may aid in obtaining a diagnosis and include computerized tomography (CT) scanning and magnetic resonance imaging (MRI). During CT scanning, a computer and x-rays are used to create a film showing cross-sectional images of certain tissue structures. An MRI uses a magnetic field and radio waves to produce cross-sectional images of particular organs and bodily tissues. CT scanning or an MRI may reveal characteristic changes in the brain in individuals with neuroacanthocytosis.
Additional tests may be performed to help confirm a diagnosis of neuroacanthocytosis including measuring serum creatine kinase (which is often elevated in chorea-acanthocytosis and McLeod syndrome) and electromyography, a test that can determine the health of muscles and nerves and can detect nerve dysfunction.
An electroencephalogram (EEG), a test which measures the electrical activity of the brain, may show changes in brain function over time that are indicative of neurodegeneration. An electrocardiogram (ECG) is a test that measures the electrical activity of the heart and may be performed to detect cardiomyopathy or other heart abnormalities.
A blood test is available at present on a research basis to detect chorein in the blood in order to confirm the diagnosis of chorea-acanthocytosis.
Blood tests can also be used for Kell blood typing in order to confirm or rule out McLeod syndrome. Blood tests can reveal absent expression of the Kx erythrocyte antigen and reduced expression of Kell blood group antigens that characterizes McLeod syndrome.
A diagnosis of a neuroacanthocytosis syndrome can be confirmed by molecular genetic testing that identifies the characteristic gene mutation associated with a particular disorder.
There is no curative treatment for neuroacanthocytosis. Treatment is directed toward the specific symptoms that are apparent in each individual. Treatment may require the coordinated efforts of a team of specialists. Pediatricians, neurologists, psychiatrists, surgeons, cardiologists, speech pathologists, social workers and other healthcare professionals may need to systematically and comprehensively plan an affect child's treatment.
Certain antipsychotic medications known as dopamine-receptor blocking drugs may be used to treat both psychiatric symptoms and chorea associated with neuroacanthocytosis. These drugs include haloperidol, tiapride, clozapine, quetiapine and tetrabenazine. Dopamine is a neurotransmitter, a chemical that modifies, amplifies or transmits nerve impulses from one nerve cell (neuron) to another, enabling nerve cells to communicate. Dopamine is critical for the proper function of certain processes of the brain especially those that control movement.
Additional antipsychotic medications as well as antidepressants and sedatives may be used to treat some individuals with neuroacanthocytosis. Psychiatric symptoms are treated with conventional therapies as symptoms become apparent.
Anti-seizure medications (anti-convulsants) such as phenytoin, clobazam, valproate and levetiracetam may be used to treat the seizures sometimes associated with neuroacanthocytosis. Anti-seizure medications can also be of benefit in treating psychiatric symptoms. Certain anti-seizure medications such as carbamazepine and lamotrigine can worsen involuntary movements and should be avoided.
Botulinum toxin has been used to treat dystonia associated with neuroacanthocytosis. The botulinum toxin is injected directly into the muscle(s) to relax the muscle and reduce or eliminate spasms. The therapeutic effects of the injections may not become obvious before five to 10 days. Injections with botulinum toxin may be very helpful in relieving dystonic muscle spasms. Injections usually need to be repeated after three to four months when symptoms return.
Because of feeding difficulties in some cases, affected individuals should be monitored for nutritional status. Nutritional support and supplementation may be necessary and, in some cases, the insertion of a feeding tube may be necessary. In addition to nutritional support, a feeding tube may be necessary to help prevent aspiration.
Additional therapies that may be used to treat individuals with neuroacanthocytosis include speech therapy, physical therapy and occupational therapy all of which should be individualized. Certain mechanical devices may be of benefit such as braces or wheelchairs. A mouth guard or bite plate may be beneficial for individuals with chronic teeth grinding or lip biting. Computer-assisted speech devices may be necessary in some cases.
Cardiac abnormalities most often associated with McLeod syndrome are treated through conventional means based upon clinical ECG findings.
Individuals with McLeod syndrome may be susceptible to adverse reactions from blood transfusions with incompatible blood. Physicians recommend that affected individuals should store or bank their own blood in case of the need for a transfusion arises.
A surgical procedure sometimes used to treat individuals with neuroacanthocytosis is deep brain stimulation, in which an electrode is placed into the portion of the brain that controls certain movements. A thin wire that passes under the skin is connected to a small battery pack that is placed under the skin near the collarbone. The electrode is used to send electrical impulses (stimulate) to the brain and interrupt aberrant nerve signals that contribute to movement disorders such as chorea or dystonia. A recent publication describing all patients with chorea-acanthocytosis who had undergone deep brain stimulation suggests that overall it is beneficial. Further information is required to determine whether people with the other forms of neuroacanthocytosis can also benefit.
Genetic counseling may be of benefit for affected individuals and their families. Other treatment is symptomatic and supportive.
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Contact for additional information about neuroacanthocytosis:
Ruth H. Walker, MB, ChB, PhD
Director, Movement Disorders Clinic,
Department of Neurology
James J. Peters VA Medical Center
Bronx, NY 10468
Department of Neurology
Mount Sinai School of Medicine
New York, NY 10029
718 584 9000 x5195
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