Persistent polyclonal binucleated B-cell lymphocytosis and MECOM gene amplification

A novel missense mutation in the MECOM gene in a Chinese boy with radioulnar synostosis with amegakaryocytic thrombocytopenia

Radioulnar synostosis with amegakaryocytic thrombocytopenia (RUSAT) type 2, caused by MDS1 and EVI1 complex locus (MECOM) gene mutations, is a rare inherited bone marrow failure syndrome (IBMFS) with skeletal anomalies, characterized by varying presentation of congenital thrombocytopenia (progressing to pancytopenia), bilateral proximal radioulnar synostosis, and other skeletal abnormalities. Due to limited knowledge and heterogenous manifestations, clinical diagnosis of the disease is challenging. Here we reported a novel MECOM mutation in a Chinese boy with typical clinical features for RUSAT-2. Trio-based whole exome sequencing of buccal swab revealed a novel heterozygous missense mutation in exon 11 of the MECOM gene (chr3:168818673; NM_001105078.3:c.2285G > A). The results strongly suggest that the variant was a germline mutation and disease-causing mutation. The patient received matched unrelated donor hematopoetic stem cell transplantation (HSCT). This finding was not only expanded the pathogenic mutation spectrum of MECOM gene, but also provided key information for clinical diagnosis and treatment of RUSAT-2.

Cytogenetics in the management of clonal chromosomal abnormalities of undetermined significance and persistent polyclonal B-cell lymphocytosis: Guidelines from the Groupe Francophone de Cytogénétique Hématologique (GFCH)

Acquired clonal chromosomal abnormalities (CAs) are usually considered to be disease-related. However, when a CA of this type is the only abnormality present (and especially in small clones), the clinical significance is unclear. Here, we review the literature on recurrent CAs whose significance is regularly subject to debate. Our objective was to help with their interpretation and develop guidelines for sex chromosome loss, trisomy 15, trisomy 8, deletion 20q and other isolated non-myelodysplastic neoplasm (MDS)-defining CAs. We suggest that non-MDS-defining CAs correspond to clonal hematopoiesis of indeterminate potential (CHIP) in the absence of cytopenia and clonal cytopenia of undetermined significance (CCUS) in the presence of cytopenia. Lastly, we review the literature on persistent polyclonal binucleated B-cell lymphocytosis; although usually benign, this condition may correspond to a premalignant state.

MECOM Deficiency: from Bone Marrow Failure to Impaired B-Cell Development

MECOM deficiency is a recently identified inborn error of immunity and inherited bone marrow failure syndrome caused by haploinsufficiency of the hematopoietic transcription factor MECOM. It is unique among inherited bone marrow failure syndromes, many of which present during later childhood or adolescence, because of the early age of onset and severity of the pancytopenia, emphasizing the importance and gene dose dependency of MECOM during hematopoiesis. B-cell lymphopenia and hypogammaglobulinemia have been described in a subset of patients with MECOM deficiency. While the mechanisms underlying the B-cell deficiency are currently unknown, recent work has provided mechanistic insights into the function of MECOM in hematopoietic stem cell (HSC) maintenance. MECOM binds to regulatory enhancers that control the expression of a network of genes essential for HSC maintenance and self-renewal. Heterozygous mutations, as seen in MECOM-deficient bone marrow failure, lead to dysregulated MECOM network expression. Extra-hematopoietic manifestations of MECOM deficiency, including renal and cardiac anomalies, radioulnar synostosis, clinodactyly, and hearing loss, have been reported. Individuals with specific genotypes have some of the systemic manifestations with isolated mild thrombocytopenia or without hematologic abnormalities, highlighting the tissue specificity of mutations in some MECOM domains. Those infants with MECOM-associated bone marrow failure require HSC transplantation for survival. Here, we review the expanding cohort of patient phenotypes and accompanying genotypes resulting in MECOM deficiency, and the proposed mechanisms underlying MECOM regulation of human HSC maintenance and B-cell development.

Patients with Persistent Polyclonal B-Cell Lymphocytosis Share the Symptomatic Criteria of Systemic Exertion Intolerance Disease

Introduction: Persistent polyclonal B-cell lymphocytosis (PPBL) is a rare and still poorly understood entity, with 90% of cases occurring in female smokers. Patients often appear tired and in pain, but the clinical symptoms remain imprecise. The main risk is the development of lymphoma in some cases. To better understand the characteristics of the fatigue associated with PPBL and study its relationship with systemic exertion intolerance disease (SEID), we analyzed the symptoms in a cohort of patients with PPBL included in the French national registry. Material and methods: An anonymous questionnaire following the recommendations of the Institute of Medicine/National Academy of Medicine for screening of the new SEID criteria was created in French and mailed to 50 patients. Results: Thirty-nine (78%) contacted patients responded. The studied population was mainly constituted of women (90%) with an average age of 50 (18–59) years. Smoking was a constant factor in all patients. A total of 28/39 (72%) respondents met the SEID symptoms criteria. Severe chronic fatigue for more than 6 months was noted in 36/39 cases (92%). Unrefreshing sleep, post-exertional malaise, cognitive impairment, and orthostatic intolerance were described in 30/39 (77%), 32/39 (82%), 28/39 (72%), and 27/39 (69%) cases, respectively. Pain (arthralgia, myalgia, headache) was present in 26/39 (67%) cases. The most prominent SEID symptoms were fatigue, followed by post-exercise discomfort and cognitive difficulties. The most disabling symptom was non-restorative sleep, followed by pain. An inflammatory and/or autoimmune context was noted in 13 patients (33%), and these comorbidities could have favored the deterioration of the general condition. Three patients also presented with fibromyalgia. However, 3 patients did not mention any complaints. Conclusion: This survey indicated that patients with PPBL most often initially presented with disabling chronic fatigue, chronic pain, and other symptoms suggestive of SEID but requiring more studies to confirm it. Education of medical staff about the symptoms of PPBL should be encouraged to better assess this peculiar condition.

Abnormal characteristic "round bottom flask" shape volume-based scattergram as a trigger to suspect persistent polyclonal B-cell lymphocytosis

BACKGROUND AND AIMS

The diagnosis of persistent polyclonal B-cell lymphocytosis (PPBL) is often challenging because of the lack of features and the overlap with the peripheral expression of splenic marginal zone lymphomas (SMZL). To obtain new clues for PPBL detection and diagnosis, all data provided by the DxH 800 analyzer (including scatter and cell population data (CPD)) was exploited and combined using a machine learning (ML) approach.

MATERIALS AND METHODS

A total 211 samples from 101 normal controls and 110 patients (PPBL and SMZL) were assessed. Age, gender, full blood count, CPD, scatter, flags and CellaVision differentials were also considered. A ML model was built for true classification purposes.

RESULTS

PPBL and SMZL shared increased absolute lymphoid counts, atypical lymphoid flag presence and CPD values (8 out of 14). A typical "round-bottom-flask" shape scattergram was described for the first time for PPBL which was also present in 51.4% of SMZL cases. The developed ML model render a global classification accuracy of 93.4%, allowing the detection of all pathological cases, with mean misclassification rates of 12% among PPBL and SMZL.

CONCLUSION

Our ML model represents a new unbiased tool than can be widely applied in the laboratory as an aid for detection of PPBL.

Polyclonal B-cell lymphocytosis in English bulldogs

Background

English bulldogs disproportionally develop an expansion of small B‐cells, which has been interpreted as B‐cell chronic lymphocytic leukemia (BCLL). However, clonality testing in these cases has often not been supportive of neoplasia.

Hypothesis

English bulldogs have a syndrome of nonneoplastic B‐cell expansion.

Animals

Eighty‐four English bulldogs with small‐sized CD21+ B‐cell lymphocytosis in the blood as determined by flow cytometry.

Methods

This is a retrospective study. We characterized this syndrome by assessing B‐cell clonality, clinical presentation, flow cytometric features, and immunoglobulin gammopathy patterns. We identified 84 cases with CD21+ lymphocytosis among 195 English bulldogs with blood samples submitted to the Colorado State University‐Clinical Immunology laboratory for immunophenotyping between 2010 and 2019. Flow cytometry features were compared to normal B‐cells and BCLL cases. PCR for antigen receptor rearrangements (PARR) by multiple immunoglobulin primers was performed to assess B‐cell clonality. A subset of cases with gammopathy were examined by protein electrophoresis, immunofixation, and immunoglobulin subclass ELISA quantification.

Results

Seventy percent (58/83) of cases had polyclonal or restricted polyclonal immunoglobulin gene rearrangements, suggesting nonmalignant B‐cell expansion. The median age of all dogs in the study was 6.8 years and 74% were male. The median (range) lymphocyte count was 22 400/μL (2000‐384 400/μL) and B‐cells had low expression of class II MHC and CD25. Splenomegaly or splenic masses were detected in 57% (26/46) of cases and lymphadenopathy in 11% (7/61). Seventy‐one percent (52/73) of cases had hyperglobulinemia and 77% (23/30) with globulin characterization had IgA ± IgM polyclonal or restricted polyclonal gammopathy patterns.

Conclusions and Clinical Importance

Polyclonal B‐cell lymphocytosis in English bulldogs is characterized by low B‐cell class II MHC and CD25 expression, splenomegaly and hyperglobulinemia consisting of increased IgA ± IgM. We hypothesize that this syndrome has a genetic basis.

MECOM-associated syndrome: a heterogeneous inherited bone marrow failure syndrome with amegakaryocytic thrombocytopenia

Heterozygous mutations in MECOM (MDS1 and EVI1 complex locus) have been reported to be causative of a rare association of congenital amegakaryocytic thrombocytopenia and radioulnar synostosis. Here we report on 12 patients with congenital hypomegakaryocytic thrombocytopenia caused by MECOM mutations (including 10 novel mutations). The mutations affected different functional domains of the EVI1 protein. The spectrum of phenotypes was much broader than initially reported for the first 3 patients; we found familial as well as sporadic cases, and the clinical spectrum ranged from isolated radioulnar synostosis with no or mild hematological involvement to severe bone marrow failure without obvious skeletal abnormality. The clinical picture included radioulnar synostosis, bone marrow failure, clinodactyly, cardiac and renal malformations, B-cell deficiency, and presenile hearing loss. No single clinical manifestation was detected in all patients affected by MECOM mutations. Radioulnar synostosis and B-cell deficiency were observed only in patients with mutations affecting a short region in the C-terminal zinc finger domain of EVI1. We propose the term MECOM-associated syndrome for this heterogeneous hereditary disease and inclusion of MECOM sequencing in the diagnostic workup of congenital bone marrow failure.