Abnormal red cell structure and function in neuroacanthocytosis

Morphometric and Nanomechanical Screening of Peripheral Blood Cells with Atomic Force Microscopy for Label-Free Assessment of Alzheimer's Disease, Parkinson's Disease, and Amyotrophic Lateral Sclerosis

Neurodegenerative disorders (NDDs) are complex, multifactorial disorders with significant social and economic impact in today's society. NDDs are predicted to become the second-most common cause of death in the next few decades due to an increase in life expectancy but also to a lack of early diagnosis and mainly symptomatic treatment. Despite recent advances in diagnostic and therapeutic methods, there are yet no reliable biomarkers identifying the complex pathways contributing to these pathologies. The development of new approaches for early diagnosis and new therapies, together with the identification of non-invasive and more cost-effective diagnostic biomarkers, is one of the main trends in NDD biomedical research. Here we summarize data on peripheral biomarkers, biofluids (cerebrospinal fluid and blood plasma), and peripheral blood cells (platelets (PLTs) and red blood cells (RBCs)), reported so far for the three most common NDDs-Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). PLTs and RBCs, beyond their primary physiological functions, are increasingly recognized as valuable sources of biomarkers for NDDs. Special attention is given to the morphological and nanomechanical signatures of PLTs and RBCs as biophysical markers for the three pathologies. Modifications of the surface nanostructure and morphometric and nanomechanical signatures of PLTs and RBCs from patients with AD, PD, and ALS have been revealed by atomic force microscopy (AFM). AFM is currently experiencing rapid and widespread adoption in biomedicine and clinical medicine, in particular for early diagnostics of various medical conditions. AFM is a unique instrument without an analog, allowing the generation of three-dimensional cell images with extremely high spatial resolution at near-atomic scale, which are complemented by insights into the mechanical properties of cells and subcellular structures. Data demonstrate that AFM can distinguish between the three pathologies and the normal, healthy state. The specific PLT and RBC signatures can serve as biomarkers in combination with the currently used diagnostic tools. We highlight the strong correlation of the morphological and nanomechanical signatures between RBCs and PLTs in PD, ALS, and AD.

Probing Red Blood Cell Membrane Microviscosity Using Fluorescence Anisotropy Decay Curves of the Lipophilic Dye PKH26

Red blood cell (RBC) aggregation and deformation are governed by the molecular processes occurring on the membrane. Since several social important diseases are accompanied by alterations in RBC aggregation and deformability, it is important to develop a diagnostic parameter of RBC membrane structural integrity and stability. In this work, we propose membrane microviscosity assessed by time-resolved fluorescence anisotropy of the lipophilic PKH26 fluorescent probe as a diagnostic parameter. We measured the fluorescence decay curves of the PKH26 probe in the RBC membrane to establish the optimal parameters of the developed fluorescence assay. We observed a complex biphasic profile of the fluorescence anisotropy decay characterized by two correlation times corresponding to the rotational diffusion of free PKH26, and membrane-bounded molecules of the probe. The developed assay allowed us to estimate membrane microviscosity ηm in the range of 100-500 cP depending on the temperature, which paves the way for assessing RBC membrane properties in clinical applications as predictors of blood microrheological abnormalities.

Changes in Blood Cell Deformability in Chorea-Acanthocytosis and Effects of Treatment With Dasatinib or Lithium

Misshaped red blood cells (RBCs), characterized by thorn-like protrusions known as acanthocytes, are a key diagnostic feature in Chorea-Acanthocytosis (ChAc), a rare neurodegenerative disorder. The altered RBC morphology likely influences their biomechanical properties which are crucial for the cells to pass the microvasculature. Here, we investigated blood cell deformability of five ChAc patients compared to healthy controls during up to 1-year individual off-label treatment with the tyrosine kinase inhibitor dasatinib or several weeks with lithium. Measurements with two microfluidic techniques allowed us to assess RBC deformability under different shear stresses. Furthermore, we characterized leukocyte stiffness at high shear stresses. The results showed that blood cell deformability–including both RBCs and leukocytes - in general was altered in ChAc patients compared to healthy donors. Therefore, this study shows for the first time an impairment of leukocyte properties in ChAc. During treatment with dasatinib or lithium, we observed alterations in RBC deformability and a stiffness increase for leukocytes. The hematological phenotype of ChAc patients hinted at a reorganization of the cytoskeleton in blood cells which partly explains the altered mechanical properties observed here. These findings highlight the need for a systematic assessment of the contribution of impaired blood cell mechanics to the clinical manifestation of ChAc.

Morphometry and Stiffness of Red Blood Cells—Signatures of Neurodegenerative Diseases and Aging

Human red blood cells (RBCs) are unique cells with the remarkable ability to deform, which is crucial for their oxygen transport function, and which can be significantly altered under pathophysiological conditions. Here we performed ultrastructural analysis of RBCs as a peripheral cell model, looking for specific signatures of the neurodegenerative pathologies (NDDs)—Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease (AD), utilizing atomic force (AFM) and conventional optical (OM) microscopy. We found significant differences in the morphology and stiffness of RBCs isolated from patients with the selected NDDs and those from healthy individuals. Neurodegenerative pathologies’ RBCs are characterized by a reduced abundance of biconcave discoid shape, lower surface roughness and a higher Young’s modulus, compared to healthy cells. Although reduced, the biconcave is still the predominant shape in ALS and AD cells, while the morphology of PD is dominated by crenate cells. The features of RBCs underwent a marked aging-induced transformation, which followed different aging pathways for NDDs and normal healthy states. It was found that the diameter, height and volume of the different cell shape types have different values for NDDs and healthy cells. Common and specific morphological signatures of the NDDs were identified.

COVID-19 Lung Pathogenesis in SARS-CoV-2 Autopsy Cases

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a major public health issue. COVID-19 is considered an airway/multi-systemic disease, and demise has been associated with an uncontrolled immune response and a cytokine storm in response to the virus. However, the lung pathology, immune response, and tissue damage associated with COVID-19 demise are poorly described and understood due to safety concerns. Using post-mortem lung tissues from uninfected and COVID-19 deadly cases as well as an unbiased combined analysis of histology, multi-viral and host markers staining, correlative microscopy, confocal, and image analysis, we identified three distinct phenotypes of COVID-19-induced lung damage. First, a COVID-19-induced hemorrhage characterized by minimal immune infiltration and large thrombus; Second, a COVID-19-induced immune infiltration with excessive immune cell infiltration but no hemorrhagic events. The third phenotype correspond to the combination of the two previous ones. We observed the loss of alveolar wall integrity, detachment of lung tissue pieces, fibroblast proliferation, and extensive fibrosis in all three phenotypes. Although lung tissues studied were from lethal COVID-19, a strong immune response was observed in all cases analyzed with significant B cell and poor T cell infiltrations, suggesting an exhausted or compromised immune cellular response in these patients. Overall, our data show that SARS-CoV-2-induced lung damage is highly heterogeneous. These individual differences need to be considered to understand the acute and long-term COVID-19 consequences.

The Erythrocyte Sedimentation Rate and Its Relation to Cell Shape and Rigidity of Red Blood Cells from Chorea-Acanthocytosis Patients in an Off-Label Treatment with Dasatinib

Background: Chorea-acanthocytosis (ChAc) is a rare hereditary neurodegenerative disease with deformed red blood cells (RBCs), so-called acanthocytes, as a typical marker of the disease. Erythrocyte sedimentation rate (ESR) was recently proposed as a diagnostic biomarker. To date, there is no treatment option for affected patients, but promising therapy candidates, such as dasatinib, a Lyn-kinase inhibitor, have been identified. Methods: RBCs of two ChAc patients during and after dasatinib treatment were characterized by the ESR, clinical hematology parameters and the 3D shape classification in stasis based on an artificial neural network. Furthermore, mathematical modeling was performed to understand the contribution of cell morphology and cell rigidity to the ESR. Microfluidic measurements were used to compare the RBC rigidity between ChAc patients and healthy controls. Results: The mechano-morphological characterization of RBCs from two ChAc patients in an off-label treatment with dasatinib revealed differences in the ESR and the acanthocyte count during and after the treatment period, which could not directly be related to each other. Clinical hematology parameters were in the normal range. Mathematical modeling indicated that RBC rigidity is more important for delayed ESR than cell shape. Microfluidic experiments confirmed a higher rigidity in the normocytes of ChAc patients compared to healthy controls. Conclusions: The results increase our understanding of the role of acanthocytes and their associated properties in the ESR, but the data are too sparse to answer the question of whether the ESR is a suitable biomarker for treatment success, whereas a correlation between hematological and neuronal phenotype is still subject to verification.

Acanthocyte Sedimentation Rate as a Diagnostic Biomarker for Neuroacanthocytosis Syndromes: Experimental Evidence and Physical Justification

(1) Background: Chorea-acanthocytosis and McLeod syndrome are the core diseases among the group of rare neurodegenerative disorders called neuroacanthocytosis syndromes (NASs). NAS patients have a variable number of irregularly spiky erythrocytes, so-called acanthocytes. Their detection is a crucial but error-prone parameter in the diagnosis of NASs, often leading to misdiagnoses. (2) Methods: We measured the standard Westergren erythrocyte sedimentation rate (ESR) of various blood samples from NAS patients and healthy controls. Furthermore, we manipulated the ESR by swapping the erythrocytes and plasma of different individuals, as well as replacing plasma with dextran. These measurements were complemented by clinical laboratory data and single-cell adhesion force measurements. Additionally, we followed theoretical modeling approaches. (3) Results: We show that the acanthocyte sedimentation rate (ASR) with a two-hour read-out is significantly prolonged in chorea-acanthocytosis and McLeod syndrome without overlap compared to the ESR of the controls. Mechanistically, through modern colloidal physics, we show that acanthocyte aggregation and plasma fibrinogen levels slow down the sedimentation. Moreover, the inverse of ASR correlates with the number of acanthocytes (R2=0.61, p=0.004). (4) Conclusions: The ASR/ESR is a clear, robust and easily obtainable diagnostic marker. Independently of NASs, we also regard this study as a hallmark of the physical view of erythrocyte sedimentation by describing anticoagulated blood in stasis as a percolating gel, allowing the application of colloidal physics theory.

The Relationship Between Aggregation and Deformability of Red Blood Cells in Health and Disease

The molecular organization of the membrane of the red blood cell controls cell morphology and function and is thereby a main determinant of red blood cell homeostasis in the circulation. The role of membrane organization is prominently reflected in red blood cell deformation and aggregation. However, there is little knowledge on whether they are controlled by the same membrane property and if so, to what extent. To address the potential interdependence of these two parameters, we measured deformation and aggregation in a variety of physiological as well as pathological conditions. As a first step, we correlated a number of deformability and aggregation parameters in red blood cells from healthy donors, which we obtained in the course of our studies on red blood cell homeostasis in health and disease. This analysis yielded some statistically significant correlations. Also, we found that most of these correlations were absent in misshapen red blood cells that have an inborn defect in the interaction between the membrane and the cytoskeleton. The observations suggest that deformability and aggregation share at least one common, membrane-related molecular mechanism. Together with data obtained after treatment with various agents known to affect membrane organization in vitro, our findings suggest that a phosphorylation-controlled interaction between the cytoskeleton and the integral membrane protein band 3 is part of the membrane-centered mechanism that plays a role in deformability as well as aggregation.

The impact of circulation in a heart-lung machine on function and survival characteristics of red blood cells

Extracorporeal circulation is accompanied by changes in red blood cell morphology and structural integrity that affect cell function and survival, and thereby may contribute to the various side effects of heart–lung machine‐assisted surgery. Our main objectives were to determine the effect of circulation of red blood cells in a stand‐alone extracorporeal circuit on several parameters that are known to be affected by, as well as contribute to red blood cell aging. As a source of RBCs, we employed blood bank storage units of different ages. In order to assess the relevance of our in vitro observations for the characterization of extracorporal circulation technology, we compared these changes in those of patients undergoing extracorporeal circulation‐assisted cardiac surgery. Our results show that circulation in a heart–lung machine is accompanied by changes in red blood cell volume, an increase in osmotic fragility, changes in deformability and aggregation behavior, and alterations in the exposure of phosphatidylserine and in microvesicle generation. RBCs from 1‐week‐old concentrates showed the highest similarities with the in vivo situation. These changes in key characteristics of the red blood cell aging process likely increase the susceptibility of red blood cells to the various mechanical, osmotic, and immunological stress conditions encountered during and after surgery in the patient’s circulation, and thereby contribute to the side effects of surgery. Thus, aging‐related parameters in red blood cell structure and function provide a foundation for the validation and improvement of extracorporeal circulation technology.

Red Blood Cell Homeostasis and Altered Vesicle Formation in Patients With Paroxysmal Nocturnal Hemoglobinuria

A subset of the red blood cells (RBCs) of patients with paroxysmal nocturnal hemoglobinuria (PNH) lacks GPI-anchored proteins. Some of these proteins, such as CD59, inhibit complement activation and protect against complement-mediated lysis. This pathology thus provides the possibility to explore the involvement of complement in red blood cell homeostasis and the role of GPI-anchored proteins in the generation of microvesicles (MVs) in vivo. Detailed analysis of morphology, volume, and density of red blood cells with various CD59 expression levels from patients with PNH did not provide indications for a major aberration of the red blood cell aging process in patients with PNH. However, our data indicate that the absence of GPI-anchored membrane proteins affects the composition of red blood cell-derived microvesicles, as well as the composition and concentration of platelet-derived vesicles. These data open the way toward a better understanding on the pathophysiological mechanism of PNH and thereby to the development of new treatment strategies.

Oxidative Stress in Autistic Children Alters Erythrocyte Shape in the Absence of Quantitative Protein Alterations and of Loss of Membrane Phospholipid Asymmetry

Red blood cells (RBCs) from people affected by autism spectrum disorders (ASDs) are a target of oxidative stress. By scanning electron microscopy, we analyzed RBC morphology from 22 ASD children and show here that only 47.5 ± 3.33% of RBC displayed the typical biconcave shape, as opposed to 87.5 ± 1.3% (mean ± SD) of RBC from 21 sex- and age-matched healthy typically developing (TD) controls. Codocytes and star-shaped cells accounted for about 30% of all abnormally shaped ASD erythrocytes. RBC shape alterations were independent of the anticoagulant used (Na₂-EDTA or heparin) and of different handling procedures preceding glutaraldehyde fixation, thus suggesting that they were not artefactual. Incubation for 24 h in the presence of antioxidants restored normal morphology in most erythrocytes from ASD patients. By Coomassie staining, as well as Western blotting analysis of relevant proteins playing a key role in the membrane-cytoskeleton organization, we were unable to find differences in RBC ghost composition between ASD and normal subjects. Phosphatidylserine (PS) exposure towards the extracellular membrane domain was examined in both basal and erythroptosis-inducing conditions. No differences were found between ASD and TD samples except when the aminophospholipid translocase was blocked by N-ethylmaleimide, upon which an increased amount of PS was found to face the outer membrane in RBC from ASD. These complex data are discussed in the light of the current understanding of the mode by which oxidative stress might affect erythrocyte shape in ASD and in other pathological conditions.

Disturbed Red Blood Cell Structure and Function: An Exploration of the Role of Red Blood Cells in Neurodegeneration

The structure of red blood cells is affected by many inborn and acquired factors, but in most cases this does not seem to affect their function or survival in physiological conditions. Often, functional deficits become apparent only when they are subjected to biochemical or mechanical stress in vitro, or to pathological conditions in vivo. Our data on the misshapen red blood cells of patients with neuroacanthocytosis illustrate this general mechanism: an abnormal morphology is associated with an increase in the susceptibility of red blood cells to osmotic and mechanical stress, and alters their rheological properties. The underlying mutations may not only affect red cell function, but also render neurons in specific brain areas more susceptible to a concomitant reduction in oxygen supply. Through this mechanism, an increased susceptibility of already compromised red blood cells to physiological stress conditions may constitute an additional risk factor in vulnerable individuals. Also, susceptibility may be induced or enhanced by systemic pathological conditions such as inflammation. An exploration of the literature suggests that disturbed red blood cell function may play a role in the pathophysiology of various neurodegenerative diseases. Therefore, interventions that reduce the susceptibility of red blood cells to physiological and pathological stress may reduce the extent or progress of neurodegeneration.

Changes in Red Blood Cell membrane lipid composition: A new perspective into the pathogenesis of PKAN

Pantothenate Kinase-Associated Neurodegeneration (PKAN) is a form of Neurodegeneration with Brain Iron Accumulation (NBIA) associated with mutations in the pantothenate kinase 2 gene (PANK2). The PANK2 catalyzes the first step of coenzyme A (CoA) biosynthesis, a pathway producing an essential cofactor that plays a key role in energy and lipid metabolism. The majority of PANK2 mutations reduces or abolishes the activity of the enzyme. In around 10% of cases with PKAN, the presence of deformed red blood cells with thorny protrusions in the circulation has been detected. Changes in membrane protein expression and assembly during erythropoiesis were previously explored in patients with PKAN. However, data on red blood cell membrane phospholipid organization are still missing in this disease. In this study, we performed lipidomic analysis on red blood cells from Italian patients affected by PKAN with a particular interest in membrane physico-chemical properties. We showed an increased number of small red blood cells together with membrane phospholipid alteration, particularly a significant increase in sphingomyelin (SM)/phosphatidylcholine (PC) and SM/phosphatidylethanolamine (PE) ratios, in subjects with PKAN. The membrane structural abnormalities were associated with membrane fluidity perturbation. These morphological and functional characteristics of red blood cells in patients with PKAN offer new possible tools in order to shed light on the pathogenesis of the disease and to possibly identify further biomarkers for clinical studies.

A new molecular link between defective autophagy and erythroid abnormalities in chorea-acanthocytosis

Chorea-acanthocytosis is one of the hereditary neurodegenerative disorders known as the neuroacanthocytoses. Chorea-acanthocytosis is characterized by circulating acanthocytes deficient in chorein, a protein of unknown function. We report here for the first time that chorea-acanthocytosis red cells are characterized by impaired autophagy, with cytoplasmic accumulation of active Lyn and of autophagy-related proteins Ulk1 and Atg7. In chorea-acanthocytosis erythrocytes, active Lyn is sequestered by HSP90-70 to form high-molecular-weight complexes that stabilize and protect Lyn from its proteasomal degradation, contributing to toxic Lyn accumulation. An interplay between accumulation of active Lyn and autophagy was found in chorea-acanthocytosis based on Lyn coimmunoprecipitation with Ulk1 and Atg7 and on the presence of Ulk1 in Lyn-containing high-molecular-weight complexes. In addition, chorein associated with Atg7 in healthy but not in chorea-acanthocytosis erythrocytes. Electron microscopy detected multivesicular bodies and membrane remnants only in circulating chorea-acanthocytosis red cells. In addition, reticulocyte-enriched chorea-acanthocytosis red cell fractions exhibited delayed clearance of mitochondria and lysosomes, further supporting the impairment of authophagic flux. Because autophagy is also important in erythropoiesis, we studied in vitro CD34+-derived erythroid precursors. In chorea-acanthocytosis, we found (1) dyserythropoiesis; (2) increased active Lyn; (3) accumulation of a marker of autophagic flux and autolysososme degradation; (4) accumlation of Lamp1, a lysosmal membrane protein, and LAMP1-positive aggregates; and (5) reduced clearance of lysosomes and mitochondria. Our results uncover in chorea-acanthocytosis erythroid cells an association between accumulation of active Lyn and impaired autophagy, suggesting a link between chorein and autophagic vesicle trafficking in erythroid maturation.

The Proteome of the Red Blood Cell: An Auspicious Source of New Insights into Membrane-Centered Regulation of Homeostasis

During the past decade, the hand-in-hand development of biotechnology and bioinformatics has enabled a view of the function of the red blood cell that surpasses the supply of oxygen and removal of carbon dioxide. Comparative proteomic inventories have yielded new clues to the processes that regulate membrane-cytoskeleton interactions in health and disease, and to the ways by which red blood cells communicate with their environment. In addition, proteomic data have revealed the possibility that many, hitherto unsuspected, metabolic processes are active in the red blood cell cytoplasm. Recent metabolomic studies have confirmed and expanded this notion. Taken together, the presently available data point towards the red blood cell membrane as the hub at which all regulatory processes come together. Thus, alterations in the association of regulatory proteins with the cell membrane may be a sine qua non for the functional relevance of any postulated molecular mechanism. From this perspective, comparative proteomics centered on the red blood cell membrane constitute a powerful tool for the identification and elucidation of the physiologically and pathologically relevant pathways that regulate red blood cell homeostasis. Additionally, this perspective provides a focus for the interpretation of metabolomic studies, especially in the development of biomarkers in the blood.

The involvement of erythrocyte metabolism in organismal homeostasis in health and disease

Historically, study of erythrocyte homeostasis has focussed on the survival of erythrocytes in the blood bank and, especially in pathological circumstances, on the mechanisms leading to accelerated aging and removal from the circulation. Recent proteomic and metabolomic data suggest that erythrocyte metabolism involves more than ATP production and transport of oxygen and carbondioxide; is subject to regulation; and is likely to reflect organismal metabolism. Also, it has become clear that systemic diseases affect erythrocyte homeostasis. The perspectives emerging from these data include new possibilities to manipulate erythrocyte function and survival in vivo, and thereby organismal homeostasis.

Red Blood Cell Homeostasis: Pharmacological Interventions to Explore Biochemical, Morphological and Mechanical Properties

During their passage through the circulation, red blood cells (RBCs) encounter severe physiological conditions consisting of mechanical stress, oxidative damage and fast changes in ionic and osmotic conditions. In order to survive for 120 days, RBCs adapt to their surroundings by subtle regulation of membrane organization and metabolism. RBC homeostasis depends on interactions between the integral membrane protein band 3 with other membrane and cytoskeletal proteins, and with key enzymes of various metabolic pathways. These interactions are regulated by the binding of deoxyhemoglobin to band 3, and by a signaling network revolving around Lyn kinase and Src family kinase-mediated phosphorylation of band 3. Here we show that manipulation of the interaction between the lipid bilayer and the cytoskeleton, using various pharmacological agents that interfere with protein-protein interactions and membrane lipid organization, has various effects on: (1) morphology, as shown by high resolution microscopy and quantitative image analysis; (2) organization of membrane proteins, as indicated by immunofluorescence confocal microscopy and quantitative as well as qualitative analysis of vesicle generation; (3) membrane lipid organization, as indicated by flow cytometric analysis of phosphatidylserine exposure; (4) deformability, as assessed in capillary-mimicking circumstances using a microfluidics system; (5) deformability as determined using a spleen-mimicking device; (6) metabolic activity as indicated by metabolomics. Our data show that there is a complex relationship between red cell morphology, membrane organization and deformability. Also, our data show that red blood cells have a relatively high resistance to disturbance of membrane organization in vitro, which may reflect their capacity to withstand mechanical, oxidative and osmotic stress in vivo.

Is postoperative encephalopathy with choreoathetosis an acquired form of neuroacanthocytosis?

Postoperative encephalopathy with choreoathetosis ("postpump chorea") is a rare complication of open-heart surgery and, in particular, the employment of a cardiopulmonary bypass pump. It almost exclusively occurs in young children. While risk factors and the underlying histopathology have been identified, the pathogenesis of postpump chorea, crucially, remains largely unknown. Transient cerebral hypoperfusion associated with cardiopulmonary bypass is considered a likely candidate mechanism, but the evidence is insufficient and inconclusive. It is hypothesized in this article, that postpump chorea may be caused by mechanical trauma to red blood cells and resulting acanthocytosis. These dysfunctional erythrocytes could then lead to damage to the globus pallidus and disease development akin to that presumed in neuroacanthocytosis. In patients with neuroacanthocytosis an association between acanthocytosis and basal ganglia pathology has been suggested. To test the mechanism hypothesized here, the effects of cardiopulmonary bypass on erythrocyte morphology and function could be systematically tested in children undergoing cardiac surgery. Ideally, the extent of erythrocyte damage could be correlated with the risk of developing postpump chorea. Finally, if the proposed hypothesis is supported by empirical findings, efforts to reduce blood cell damage during extracorporeal circulation in children might prevent this devastating complication.

Neuroacanthocytosis: Observations, Theories and Perspectives on the Origin and Significance of Acanthocytes

The presence of acanthocytes in the blood is characteristic of patients suffering from neuroacanthocytosis (NA). Recent studies have described abnormal phosphorylation of the proteins involved in connecting the membrane and cytoskeleton in patient-derived erythrocytes. The involvement of lipids in the underlying signaling pathways and recent reports on in vitro disease-associated lipid alterations support renewed research into lipid composition, signal transduction, and metabolism in patient erythrocytes. In addition to morphology, changes in membrane organization affect erythrocyte function and survival. Patient erythrocytes may have a decreased ability to deform, and this may contribute to accelerated erythrocyte removal and a decreased oxygen supply, especially in vulnerable brain regions. The presently available data indicate that acanthocytes are likely to originate in the bone marrow, making erythropoiesis an obvious new focus in NA research. Moreover, new, detailed morphological observations indicate that acanthocytes may be the tip of the iceberg with regard to misshapen erythrocytes in the circulation of patients with NA.

A systematic assessment of patient erythrocyte morphology, deformability, oxygen delivery, and metabolism will be instrumental in determining the putative contribution of erythrocyte function to NA clinical symptoms.