ALBERT

Description: The Hereditary Hemolytic Anemias (HHAs) are a genetically heterogeneous group of anemias characterized by decreased red blood cell (RBC) survival because of defects in hemoglobin, RBC membrane proteins or enzymes. The diagnosis of this group of disorders is complex and challenging requiring analysis of the morphology of RBCs, hemoglobin electrophoresis, and a battery of phenotypic assays. The phenotypic analysis is often problematic in transfusion dependent patients or at times of presentation with a hemolytic crisis as transfused blood or reticulocytosis confounds diagnostic testing. Molecular genetic testing has grown in popularity in the diagnosis of hereditary hemolytic anemias as it is not affected by transfusions or other clinical variables and provides additional insight into the mechanism of the disease. We have developed a Next Generation Sequencing (NGS) panel for HHA due to RBC membrane disorders and enzymopathies and congenital dyserythropoietic anemias (CDA). CDAs, although collectively rare, are included in the panel as they are occasionally misdiagnosed as hereditary spherocytosis (HS) due to their clinical characteristics of hemolysis, increased osmotic fragility, and splenomegaly albeit with inadequate reticulocytosis We reviewed the results of 282 sequential HHA/CDA panels testing for patients with suspected HHA or CDA diagnosis, performed and interpreted at Cincinnati Children's Hospital Medical Center between 1/2013-5/2016. Forty-three samples were omitted from the final analysis due to diagnosis of other disorders, indicating that negative results were true-negatives. For the analysis of the remaining 239 panels, all results were reviewed and categorized based on the type of testing ordered: comprehensive HHA/CDA (32 genes), RBC membrane disorders (13 genes), RBC enzyme disorders (14 genes), or CDA (6 genes). The protein-coding exons plus 25 bases of exon-intron junction as well as promoter sequences were included in the design. Genomic DNA was isolated from blood and target regions were enriched using the Haloplex technology. Enriched samples were then sequenced on an Illumina MiSeq benchtop sequencer with 150 base pair, paired-end reads. Sequencing reads were aligned to the human genome reference sequence and analysis of coverage and variants was completed using NextGENe software. All positive findings were confirmed by Sanger sequencing. These 239 panels included 159 (66.5%) comprehensive HHA/CDA panels, 41 (17.2%) RBC membrane disorder panels, 10 (4.2%) RBC enzyme disorder panels, and 29 (12.1%) CDA panels. Overall, a diagnosis was confirmed or identified in 135 (56.5%) patients with specific genotype of hereditary spherocytosis in 52 patients; hereditary elliptocytosis in 15 patients; hereditary pyropoikilocytosis in 7 patients; hereditary stomatocytosis/xerocytosis in 12 patients; South East Asian Ovalocytosis in 1 patient; G6PD deficiency in 15 patients; pyruvate kinase deficiency in 17 patients; other rare RBC enzymopathies in 6 patients; and CDA in 10 patients. The clinical performance of RBC membrane disorder and RBC enzyme disorder panels were comparable between 68-70% in reaching a final diagnosis, while CDA panel confirmed final diagnosis in only 20% of suspected cases. The overall low prevalence, complexity of diagnosis with findings of dyserythropoiesis in bone marrow studies in patients with severe HHA, and evidence of locus heterogeneity in CDA might explain this result. Among patients with suspected RBC membrane disorders, approximately 14% were eventually diagnosed with hereditary xerocytosis (HX). HX diagnosis is critical to make in such patients since splenectomy is contraindicated due to the high risk of life-threatening thrombophilia complications. In more than half (56.5%) of all cases with suspected hereditary hemolytic anemia, genetic testing provided or confirmed the diagnosis and optimized patients' clinical management. Further genetic counseling and testing for other at-risk family members was made possible by achieving molecular diagnosis. Genetic testing substantially altered management in approximately 14% of cases with suspected RBC membrane disorders due to the diagnosis of HX. In conclusion, genetic testing has a significant clinical utility and may facilitate and improve diagnosis, prognosis and management considerations in patients with hereditary hemolytic or dyserythropoietic anemia. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures No relevant conflicts of interest to declare.

Description: Erythroblastic islands (EBIs) are a hallmark of mammalian erythropoiesis consisting of a central macrophage surrounded by and interacting closely with maturing erythroblasts. While it is generally accepted that the island macrophages play an important role in erythropoiesis, the inability to identify and isolate this macrophage subpopulation has limited our understanding of their functional involvement. Previous studies have relied on immunohistochemistry/immunofluorescence in situ or in vitro. More recently, flow cytometry was used to characterize EBI formation and the immunophenotype of the central macrophages in murine erythroblastic islands. These approaches provide either morphological/structural information or high-throughput quantification, but not both, and often carry the expectation that all EBI macrophages have similar phenotype (F4/80+/CD169+/VCAM1+ for example), and thus potentially overlook critical information about the nature and biology of the islands and the central macrophages. We have developed a novel method for analysis and characterization of EBI macrophages from hematopoietic tissues using multispectral imaging flow cytometry, which combines the high-throughput advantage of flow cytometry with the morphology and fluorescence details obtained from microscopy. This method allows automated, non-biased evaluation of the EBIs recovered from a sample, their number, mean size, as well as structural and morphological details of the central macrophages and associated erythroblasts. Most importantly, the images, combined with the fluorescence similarity feature, enables the evaluation of co-expression of any phenotypic markers that may be used to identify the macrophages which is crucial since some antigens used to identify macrophages (e.g. CD45, CD11b) may also be expressed on non-erythroid cells associated with the islands instead of, or in addition to, the central macrophage itself. We used this method to confirm the expression of various markers previously reported to be expressed on the erythroblastic island macrophages by flow, including CD11b, VCAM1, F4/80, CD169, and CD163, in mouse, rat, and human bone marrow. Indeed, while a large number of studies have focused on murine erythropoiesis, the identity and role of the EBIs in other species is much less known. We confirmed expression of CD169 and VCAM1 on the F4/80+ central macrophages of murine EBIs and also identified a population of VCAM+/F4/80- central cells associated with developing erythroblasts. CD11b is abundantly expressed by non-erythroid, non-macrophage cells associated with the islands, but is not expressed significantly on the central macrophages (Figure 1). CD163, a marker of EBI macrophages in rat and human, was not detected in the murine EBIs by imaging flow cytometry, but this may be due to limitation of the antibodies tested. In contrast, anti-CD163 stained well rat and human EBI macrophages but CD11b or VCAM1 were not detected in EBIs from rat and human bone marrow respectively, raising the question of a species-specificity regarding the macrophage heterogeneity and satellite cells present within erythroblastic islands. In summary, the data presented herein demonstrate the effectiveness of this method for the analysis and characterization of EBIs and establish a new tool for future investigations of EBIs and their central macrophages in the nurturing of erythropoiesis. Figure 1 Representative image of an erythroblastic island harvested from murine bone marrow stained with F4/80-AF488 (green), CD11b-PE (blue), and CD71-BV421 (red) and analyzed by imaging flow cytometry. Figure 1. Representative image of an erythroblastic island harvested from murine bone marrow stained with F4/80-AF488 (green), CD11b-PE (blue), and CD71-BV421 (red) and analyzed by imaging flow cytometry. Disclosures No relevant conflicts of interest to declare.

Description: In this work, we utilized a parameterization model of ektacytometry to quantify the bulk rigidity of the rigid red blood cell (RBC) population in sickle cell disease (SCD) patients. Current ektacytometry techniques implement laser diffraction viscometry to estimate the RBC deformability in a whole blood sample. However, the diffraction measurement is an average of all cells present in the measured sample. By coupling an existing parameterization model of ektacytometry to an artificially rigid RBC model, we formulated an innovative system for estimating the average rigidity of the rigid RBC population in SCD blood. We demonstrated that this method could more accurately determine the bulk stiffness of the rigid RBC populations. This information could potentially help develop the ektacytometry technique as a tool for assessing disease severity in SCD patients, offering novel insights into the disease pathology and treatment.