Search

Background and objectivesThe diseases historically known as neuroacanthocytosis (NA) conditions include VPS13A disease (formerly chorea-acanthocytosis) and XK disease (formerly McLeod syndrome). Here we report a patient with a hyperkinetic syndrome associated with variants in VPS13A with a concomitant homozygous nucleotide expansion in Replication factor C, subunit 1 (RFC1) and evaluate the role of ektacytometry for the assessment of acanthocytes.MethodsInvestigations included clinical assessments, neuroimaging studies, laboratory analyses, blood smears, ektacytometry, psychometric evaluation, and genetic analyses. Using ektacytometry, an osmoscan curve is obtained yielding a diffraction pattern as a measure of average erythrocyte deformability from circular at rest to elliptical at a high shear stress. The pattern allows the derivation of several parameters (mainly EI-max, O-min and O-Hyper points). Samples from two other patients with genetically proven VPS13A disorder and XK disease and varying numbers of acanthocytes as well as from a fourth with acanthocytosis due to liver failure were also analyzed.Case presentationThe patient has impulsivity, chorea and disabling feeding dystonia refractory to treatment and 15% acanthocytes in peripheral blood. Genetic workup revealed compound heterozygous variants c.1732_1733del; p.(V578Ffs*9) and c.8282C > A, p.(S2761*) in VPS13A with absence of chorein in the blood, the latter variant is novel. In addition, he harbors a homozygous nucleotide expansion in the RFC1 gene, reported in cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS). However, the patient does not display ataxia yet. Ektacytometry revealed significantly reduced erythrocyte deformability in this patient and in another man with VPS13A disease. In contrast, the patient with XK disease had 2% acanthocytes and mild abnormalities on ektacytometry. In the three cases, ektacytometry yielded a specific pattern, different from acanthocytosis due to liver failure.ConclusionPathogenicity of the VPS13A variants is confirmed by absence of chorein, long-term follow up is required to evaluate any synergistic impact of for the underlying CANVAS mutation. New generation ektacytometry provides an objective measurement of erythrocytes’ rheological properties and may serve as a complement to blood smears. Finally, ektacytometry’s ability to detect deformability of erythrocytes in NA seems to depend on the degree of acanthocytosis.

IntroductionThe unique red blood cell (RBC) properties that characterize the rare neuroacanthocytosis syndromes (NAS) have prompted the exploration of osmotic gradient ektacytometry (Osmoscan) as a diagnostic tool for these disorders. In this exploratory study, we assessed if Osmoscans can discriminate NAS from other neurodegenerative diseases.MethodsA comprehensive assessment was conducted using Osmoscan on a diverse group of patients, including healthy controls (n = 9), neuroacanthocytosis syndrome patients (n = 6, 2 VPS13A and 4 XK disease), Parkinson’s disease patients (n = 6), Huntington’s disease patients (n = 5), and amyotrophic lateral sclerosis patients (n = 4). Concurrently, we collected and analyzed RBC indices and patients’ characteristics.ResultsStatistically significant changes were observed in NAS patients compared to healthy controls and other conditions, specifically in osmolality at minimal elongation index (Omin), maximal elongation index (EImax), the osmolality at half maximal elongation index in the hyperosmotic part of the curve (Ohyper), and the width of the curve close to the osmolality at maximal elongation index (Omax-width).DiscussionThis study represents an initial exploration of RBC properties from NAS patients using osmotic gradient ektacytometry. While specific parameters exhibited differences, only Ohyper and Omax-width yielded 100% specificity for other neurodegenerative diseases. Moreover, unique correlations between Osmoscan parameters and RBC indices in NAS versus controls were identified, such as osmolality at maximal elongation index (Omax) vs. mean cellular hemoglobin content (MCH) and minimal elongation index (EImin) vs. red blood cell distribution width (RDW). Given the limited sample size, further studies are essential to establish diagnostic guidelines based on these findings.

In many medical disciplines, red blood cells are discovered to be biomarkers since they “experience” various conditions in basically all organs of the body. Classical examples are diabetes and hypercholesterolemia. However, recently the red blood cell distribution width (RDW), is often referred to, as an unspecific parameter/marker (e.g., for cardiac events or in oncological studies). The measurement of RDW requires venous blood samples to perform the complete blood cell count (CBC). Here, we introduce Erysense, a lab-on-a-chip-based point-of-care device, to evaluate red blood cell flow properties. The capillary chip technology in combination with algorithms based on artificial neural networks allows the detection of very subtle changes in the red blood cell morphology. This flow-based method closely resembles in vivo conditions and blood sample volumes in the sub-microliter range are sufficient. We provide clinical examples for potential applications of Erysense as a diagnostic tool [here: neuroacanthocytosis syndromes (NAS)] and as cellular quality control for red blood cells [here: hemodiafiltration (HDF) and erythrocyte concentrate (EC) storage]. Due to the wide range of the applicable flow velocities (0.1–10 mm/s) different mechanical properties of the red blood cells can be addressed with Erysense providing the opportunity for differential diagnosis/judgments. Due to these versatile properties, we anticipate the value of Erysense for further diagnostic, prognostic, and theragnostic applications including but not limited to diabetes, iron deficiency, COVID-19, rheumatism, various red blood cell disorders and anemia, as well as inflammation-based diseases including sepsis.

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.