Neuroacanthocytosis Syndromes

Neuroacanthocytosis Syndromes

Overview

Neuroacanthocytosis syndromes are a group of rare, progressive neurodegenerative disorders characterized by the presence of acanthocytes (abnormally shaped red blood cells with spiky projections) in peripheral blood and progressive movement disorders, cognitive decline, and psychiatric symptoms[@jung2011]. These rare conditions provide unique insights into membrane lipid metabolism, cytoskeletal dynamics, and their relationship to neuronal function and survival[@rampoldi2004].

The term "neuroacanthocytosis" encompasses several distinct clinical entities, including chorea-acanthocytosis (ChAc) and McLeod syndrome (MLS), which share similar clinical features but have different genetic causes and pathophysiology[@walker2005]. These disorders are part of a broader group of neuroacanthocytosis syndromes that also includes abetalipoproteinemia (ABL) and pantothenate kinase-associated [neurodegeneration](/diseases/neurodegeneration) (PKAN), each with distinct underlying mechanisms[@danek2005].

Epidemiology

Neuroacanthocytosis syndromes are extremely rare, with an estimated prevalence of 1-5 per million for chorea-acanthocytosis and 1-10 per million for McLeod syndrome[@hewer2006]. The actual prevalence may be higher due to underdiagnosis, as the characteristic movement disorders can be mistaken for other conditions such as [Huntington's disease](/diseases/huntingtons) or other forms of chorea[@saiki2008].

Neuroacanthocytosis Syndromes

Overview

Neuroacanthocytosis syndromes are a group of rare, progressive neurodegenerative disorders characterized by the presence of acanthocytes (abnormally shaped red blood cells with spiky projections) in peripheral blood and progressive movement disorders, cognitive decline, and psychiatric symptoms[@jung2011]. These rare conditions provide unique insights into membrane lipid metabolism, cytoskeletal dynamics, and their relationship to neuronal function and survival[@rampoldi2004].

The term "neuroacanthocytosis" encompasses several distinct clinical entities, including chorea-acanthocytosis (ChAc) and McLeod syndrome (MLS), which share similar clinical features but have different genetic causes and pathophysiology[@walker2005]. These disorders are part of a broader group of neuroacanthocytosis syndromes that also includes abetalipoproteinemia (ABL) and pantothenate kinase-associated [neurodegeneration](/diseases/neurodegeneration) (PKAN), each with distinct underlying mechanisms[@danek2005].

Epidemiology

Neuroacanthocytosis syndromes are extremely rare, with an estimated prevalence of 1-5 per million for chorea-acanthocytosis and 1-10 per million for McLeod syndrome[@hewer2006]. The actual prevalence may be higher due to underdiagnosis, as the characteristic movement disorders can be mistaken for other conditions such as [Huntington's disease](/diseases/huntingtons) or other forms of chorea[@saiki2008].

Chorea-acanthocytosis shows no clear ethnic or geographical clustering, with cases reported worldwide[@gutsche2014]. The male-to-female ratio is approximately equal, although some studies suggest a slight male predominance in McLeod syndrome[@danek2001]. Onset typically occurs in the third to fourth decade of life, although cases have been reported spanning from adolescence to late adulthood[@bohlega2003].

Genetics and Molecular Pathophysiology

Chorea-Acanthocytosis (ChAc)

Chorea-acanthocytosis is caused by mutations in the VPS13A gene (also known as CHAC), located on chromosome 9q21[@rampoldi2001]. The VPS13A gene encodes chorein, a protein of unknown function that is highly expressed in the brain, particularly in the [basal ganglia](/brain-regions/basal-ganglia)[@kurano2006]. Over 100 pathogenic mutations have been identified, including nonsense, frameshift, splice-site, and missense mutations that result in reduced or absent chorein expression[@dobsonstone2002].

The pathophysiology of ChAc involves progressive degeneration of the [basal ganglia](/brain-regions/basal-ganglia), particularly the caudate nucleus and putamen[@bader2011]. Neuroimaging studies reveal caudate head atrophy and ventricular enlargement that correlates with clinical severity[@henkel2006]. Post-mortem studies demonstrate neuronal loss, gliosis, and reduced GABAergic [neurons](/cell-types/neurons) density in the striatum[@scheidecker2015].

The mechanism by which VPS13A mutations lead to [neurodegeneration](/diseases/neurodegeneration) remains incompletely understood. Current hypotheses suggest roles in:

• Vesicle trafficking: VPS13 proteins are involved in intracellular membrane transport between organelles[@du2020]
• Cytoskeletal organization: Chorein may interact with the actin cytoskeleton and affect membrane protein distribution[@velayosbaeza2004]
• Autophagy: Impaired autophagic flux may lead to accumulation of damaged organelles and proteins[@zhang2020]
• Iron metabolism: Altered iron handling may contribute to [oxidative stress](/mechanisms/oxidative-stress) and neuronal injury[@mazarati2021]

McLeod Syndrome (MLS)

McLeod syndrome is caused by mutations in the XK gene on the X chromosome (Xq21.3), which encodes the XK protein required for expression of the Kell blood group antigens on erythrocyte membranes[@redman1999]. The XK protein is a member of the 12-transmembrane domain transporter family and may function as a facilitative glucose transporter[@ho1994].

MLS is an X-linked disorder, with affected males showing complete absence of XK protein and the Kell blood group antigens[@cartron1995]. Female carriers may show mild expression due to X-chromosome inactivation patterns[@francke1985]. The XK protein is widely expressed, including in the brain, particularly in the [basal ganglia](/brain-regions/basal-ganglia)[@walker2006].

The [neurodegeneration](/diseases/neurodegeneration) in MLS involves the [basal ganglia](/brain-regions/basal-ganglia) and may relate to:

• Mitochondrial dysfunction: Impaired energy metabolism and increased [oxidative stress](/mechanisms/oxidative-stress)[@hara2014]
• Dysregulated iron metabolism: Elevated ferritin levels and iron accumulation in the [basal ganglia](/brain-regions/basal-ganglia)[@kawai2007]
• Excitotoxicity: Enhanced glutamatergic signaling leading to calcium overload[@danek2009]

Abetalipoproteinemia (ABL)

Abetalipoproteinemia is caused by mutations in the MTP gene (microsomal triglyceride transfer protein) on chromosome 4q23[@sharp1993]. MTP is essential for the assembly and secretion of apolipoprotein B-containing lipoproteins in the liver and intestine[@hussain2003]. The absence of apolipoprotein B-containing lipoproteins leads to fat malabsorption, very low cholesterol levels, and fat-soluble vitamin deficiency[@burnett2018].

Neurological manifestations in ABL result from deficiency of vitamin E (alpha-tocopherol), which is transported in VLDL/LDL particles[@traber2005]. The characteristic neurological features include:

• Peripheral neuropathy: Demyelinating neuropathy with loss of proprioception and reflexes[@koren2015]
• Ataxia: Cerebellar degeneration leading to gait instability[@harding1991]
• Retinitis pigmentosa: Progressive photoreceptor degeneration[@runge1986]

Clinical Features

Core Movement Disorders

The movement disorder in neuroacanthocytosis syndromes is characterized by chorea—involuntary, jerky, dance-like movements that flow from one body part to another[@bhattacharya2009]. In ChAc, chorea typically begins in the face and tongue, with subsequent spread to the limbs and trunk[@danek2008]. The chorea may be initially subtle but progressively interferes with daily activities, speech, and swallowing[@schneider2009].

In MLS, the movement disorder is often less severe than in ChAc, with a predominance of trunk chorea and less facial involvement[@jung2007]. Some patients develop parkinsonism rather than chorea, particularly in later disease stages[@martinezlage2019].

Other movement disorders that may emerge include:

• Dystonia: Sustained or intermittent muscle contractions causing abnormal postures or movements[@bader2011a]
• Tremor: Rhythmic oscillatory movements, typically rest or action tremor[@vitale2016]
• Tic-like movements: Brief, repetitive movements that may be suppressible[@malerba2020]
• Plegia: Weakness or paralysis, particularly in the orofacial region[@saiki2012]

Orolingual Motor Dysfunction

Orolingual chorea is a hallmark feature of neuroacanthocytosis, present in over 80% of patients[@kihara2010]. This involves involuntary tongue movements, lip smacking, and perioral choreiform movements that can lead to:

• Dysarthria: Slurred, variable speech with reduced intelligibility[@thomas2015]
• Dysphagia: Difficulty swallowing, increasing aspiration risk[@schneider2006]
• Weight loss: Due to feeding difficulties and increased energy expenditure[@lossos2011]
• Self-mutilation: Lip and cheek biting in severe cases[@saiki2009]

Psychiatric and Cognitive Features

Cognitive impairment develops in the majority of patients, typically presenting as a subcortical dysexecutive syndrome with:

• Executive dysfunction: Impaired planning, set-shifting, and problem-solving[@vitale2015]
• Memory deficits: Particularly for recent events and procedural learning[@roos2013]
• Behavioral changes: Irritability, apathy, and disinhibition[@walker2007]

• Depression: Present in up to 40% of patients, often preceding motor symptoms[@schrempf2015]
• Anxiety: Generalized anxiety, panic attacks, and social phobia[@lencer2014]
• Obsessive-compulsive symptoms: Repetitive behaviors and intrusive thoughts[@peetersschneider2016]
• Psychosis: Less common, but can include delusions and hallucinations[@walterfang2010]

Other Neurological Features

• Seizures: Present in approximately 20% of patients with ChAc[@m2010]
• Peripheral neuropathy: More common in MLS and ABL, less prominent in ChAc[@lossos2016]
• Myopathy: Elevated creatine kinase and mild proximal weakness in some MLS patients[@malerba2017]
• Sensory abnormalities: Reduced vibration sense and proprioception[@kawai2009]

Systemic Features

The characteristic acanthocytes are present in 15-70% of erythrocytes on peripheral blood smear[@storch2005]. In ChAc, acanthocyte count may correlate with disease severity and progression[@hara2011]. Other systemic features include:

• Elevated creatine kinase: Often 2-10 times the upper limit of normal[@rinne2004]
• Elevated transaminases: AST and ALT elevations indicating hepatic involvement[@lossos2014]
• Iron overload: Elevated ferritin and transferrin saturation in some patients[@hentati2005]

Diagnosis

Clinical Diagnosis

The diagnosis of neuroacanthocytosis syndromes is based on the combination of:

Laboratory Findings

• Peripheral blood smear: Identification of acanthocytes (15-70% of erythrocytes)[@storch2004]
• Serum creatine kinase: Elevated in 70-90% of patients[@stoll2005]
• Liver function tests: Elevated AST/ALT in 50-70%[@walker2010]
• Iron studies: Elevated ferritin in 30-40%[@jung2010]
• Vitamin levels: Low vitamin E in ABL patients[@muller1999]

Neuroimaging

MRI findings in neuroacanthocytosis include:

• Caudate atrophy: Particularly of the caudate head, visible as enlargement of the frontal horns[@henkel2006a]
• Putaminal changes: Hyperintensity or atrophy in advanced cases[@bader2008]
• Globus pallidus abnormalities: T2 hyperintensity in some patients[@henkel2005]
• White matter changes: Periventricular [white matter](/brain-regions/white-matter) hyperintensities[@tienari2012]

Genetic Testing

Molecular genetic testing is available for:

• VPS13A: Sequencing and deletion/duplication analysis for ChAc[@dobsonstone2003]
• XK: Sequencing for MLS[@redman1999a]
• MTP: Sequencing for ABL[@hooper2008]

Management

Pharmacological Treatment

Movement disorder management:

• Tetrabenazine: Reduces chorea by depleting dopamine[@jankovic2008]
• Deutetrabenazine: Similar efficacy with improved tolerability[@huntington2017]
• Antipsychotics: Haloperidol, olanzapine for severe chorea[@termsarasab2015]
• Benzodiazepines: Clonazepam for anxiety and myoclonus[@garciaborreguero2003]

• SSRIs: For depression and anxiety (sertraline, citalopram)[@schrempf2014]
• Antipsychotics: For psychosis (quetiapine, risperidone)[@pagonabarraga2012]
• Mood stabilizers: For bipolar features or severe behavioral changes[@novam2018]

• Iron chelation: For iron overload (deferoxamine, deferasirox)[@hentati2006]
• Vitamin E supplementation: Essential in ABL patients[@kayden1986]
• Coenzyme Q10: May provide mitochondrial support in some patients[@hargreaves2010]

Non-Pharmacological Interventions

• Speech therapy: For dysarthria and dysphagia management[@bak2014]
• Physical therapy: For gait training and fall prevention[@ashizawa2011]
• Occupational therapy: For activities of daily living adaptation[@ciolli2008]
• Nutritional support: Dietitian consultation for weight maintenance[@martinezlage2019a]

Experimental and Emerging Therapies

• Gene therapy: Viral vector-mediated gene delivery for VPS13A[@tieu2021]
• Protein replacement: Recombinant chorein administration[@muller2020]
• Neuroprotective agents: Targeting [oxidative stress](/mechanisms/oxidative-stress) and excitotoxicity[@chen2020]
• Cell-based therapies: Stem cell transplantation approaches[@takahashi2019]

Prognosis

The disease course is progressive, with typical survival of 15-30 years from symptom onset[@walker2006a]. Death often results from:

• Aspiration pneumonia: Due to dysphagia and chorea[@lossos2012]
• Suicide: In patients with severe depression[@schrempf2018]
• Accidental injuries: Falls and trauma[@hentati2007]
• Comorbid conditions: Cardiovascular disease[@danek2010]

• Early onset: Symptoms before age 30[@hara2013]
• Severe chorea: High chorea scores at baseline[@bhattacharya2012]
• Cognitive impairment: Early dementia[@vitale2016a]
• Psychiatric comorbidities: Severe depression or psychosis[@lencer2017]

Animal Models

Several animal models have been developed to study neuroacanthocytosis:

• VPS13A knockout mice: Show behavioral abnormalities but no clear [neurodegeneration](/diseases/neurodegeneration)[@yung2020]
• XK knockout mice: Model MLS with erythrocyte abnormalities and mild neurological deficits[@jung2011a]
• Drosophila models: Knockdown of VPS13 orthologs shows movement abnormalities[@shi2019]

Research Directions

Current research priorities include:

See Also

• [neurodegeneration](/diseases/neurodegeneration)
• [Huntington's disease](/diseases/huntingtons)
• [oxidative stress](/mechanisms/oxidative-stress)
• [Multiple Sclerosis](/diseases/multiple-sclerosis)

External Links

• [PubMed](https://pubmed.ncbi.nlm.nih.gov/)
• [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)

Pathway Diagram

References