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120. Benign Ethnic Neutropenia in a Sample of Nigerian Healthy Controls and Clozapine-Treated Schizophrenia Patients With DARC Null Variant

ABSTRACT: Abstract Background: Benign ethnic neutropenia (BEN) is the occurrence of absolute neutrophil counts (ANC) of less than 1500 cells/mm3 observed in 10% to 30% of African and Middle Eastern ancestry individuals with no increased susceptibility to pyogenic infections. Recent evidence implicates polymorphism in the Duffy Antigen Receptor for Chemokines gene (DARC) in BEN persons of African descent. Until mid-2015 in the United States, the FDA clozapine treatment guidelines for ANC monitoring were based on normative ANC values in European ancestry populations without considerations for BEN. Compared with Caucasians, African Americans are less likely to be initiated on clozapine and their treatment twice as likely to be discontinued for neutropenia. Gathering data indicate no increased agranulocytosis risk in clozapine-treated BEN individuals. Advancing knowledge of BEN pathophysiology could reduce a substantial barrier to clozapine treatment in African-American patients. Methods: We examined ANC data collected on a sample of 136 schizophrenia and 33 healthy control Yoruba participants recruited at the Federal Neuropsychiatric Hospital Yaba, Lagos. Exclusion criteria included medical conditions that could affect white blood cell counts. In the patient group, 100 had been on stable clozapine treatment (>6 months). In a subgroup of participants (n = 69), we assayed the regulatory variant (rs2814778) in the promoter of DARC (DARC -46T > C) implicated in low neutrophil counts in African-ancestry populations. Results: The sample consisted of 88 females and 81 males. Sex was not different between schizophrenia and control groups (P = .3). Age differed between schizophrenia (mean [SD], 40.15 [13.15] years) and controls (mean [SD], 29.12 [5.08] years; P < .001). The sample mean ANC was 2,557/mm3 (range 800 to 6,970); with 31% and 11% showing ANC below 2000 and 1500/mm3, respectively. The mean daily clozapine dose was 224?mg. Clozapine-treated patients had a significantly higher mean ANC (2777/mm3 [0.97]) compared with controls and non-clozapine treated patients (2238/mm3 [0.88]; P < .001). All 69 individuals assayed for rs2814778 were homozygous for the Duffy-null allele (DARC -46T > C). Conclusion: The results are consistent with reported rates of BEN in African populations, supports the safety of clozapine monitoring using lower ANC levels in BEN populations, and demonstrates the common occurrence of the African-derived “null” DARC gene variant in this sample.

SUBMITTER: Wonodi I

PROVIDER: S-EPMC5475632 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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Project description:Background: Benign ethnic neutropenia (BEN) is a hematologic condition associated with people of African ancestry and specific Middle Eastern ethnic groups. Prior genetic association studies in large population showed that rs2814778 in Duffy Antigen Receptor for Chemokines (DARC) gene, specifically DARC null red cell phenotype, was associated with BEN. However, the mechanism of this red cell phenotype leading to low white cell count remained elusive.Methods: We conducted an extreme phenotype design genome-wide association study (GWAS), analyzed ~16 million single nucleotide polymorphisms (SNP) in 1,178 African-Americans individuals from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study and replicated from 819 African-American participants in the Atherosclerosis Risk in Communities (ARIC) study. Conditional analyses on rs2814778 were performed to identify additional association signals on chromosome 1q22. In a separate cohort of healthy individuals with and without BEN, whole genome gene expression from peripheral blood neutrophils were analyzed for DARC.Results: We confirmed that rs2814778 in DARC was associated with BEN (p = 4.09×10-53). Conditioning on rs2814778 abolished other significant chromosome 1 associations. Inflammatory cytokines (IL-2, 6, and 10) in participants in the Howard University Family Study (HUFS) and Multi-Ethnic Study in Atherosclerosis (MESA) showed similar levels in individuals homozygous for the rs2814778 allele compared to others, indicating cytokine sink hypothesis played a minor role in leukocyte homeostasis. Gene expression in neutrophils of individuals with and without BEN was also similar except for low DARC expression in BEN, suggesting normal function. BEN neutrophils had slightly activated profiles in leukocyte migration and hematopoietic stem cell mobilization pathways (expression fold change <2).Conclusions: These results in humans support the notion of DARC null erythroid progenitors preferentially differentiating to myeloid cells, leading to activated DARC null neutrophils egressing from circulation to the spleen, and causing relative neutropenia. Collectively, these human data sufficiently explained the mechanism DARC null red cell phenotype causing BEN and further provided a biologic basis that BEN is clinically benign.

Project description:BackgroundBenign ethnic neutropenia (BEN) is the most common cause of chronic neutropenia seen in individuals of African, Middle Eastern and West Indian descent. This phenotype is broadly defined by an absolute neutrophil counts (ANC) below 1.8 × 109 cells/L in the absence of other causes, without an increased risk of infection. BEN has been implicated as a potential source of disparity in patients treated with clozapine, the antipsychotic of choice in treatment-resistant schizophrenia. Our main objective was to examine the current level of BEN recognition in a cohort of patients treated with clozapine and the potential impact of unidentified BEN on the initiation and maintenance of clozapine treatment.MethodsThis was an observational, retrospective analysis of patients registered with clozapine haematological monitoring systems in two large mental health trusts, chosen because they serve an ethnically diverse population. The first objective was to establish certified BEN prevalence in current users of clozapine. The second objective was to explore the stage of treatment at which BEN was identified. The third objective was to evaluate the extent of unrecognised BEN in patients registered on the Central Non-Rechallenge Database (CNRD), a database for patients whose haematological parameters fall below set thresholds when receiving clozapine treatment, meaning they cannot ordinarily be prescribed clozapine again.ResultsThe study population comprised of 2020 patients on the clozapine register. 111 patients were monitored under BEN criteria. BEN was mostly identified after a below threshold haematological result or clozapine rechallenge (68%) compared to at clozapine initiation (32%). Eight of the 18 (42%) black patients registered on the CNRD were classified as BEN after assessment by a haematologist. Of these 8 patients, none would have met CNRD criteria again if monitored with BEN criteria at clozapine initiation.ConclusionsCurrent evidence suggests that BEN remains an uncommonly recognised haematological phenotype. Improved timely identification of BEN will reduce unnecessary interruption or discontinuation of clozapine treatment. Our results suggest consideration should also be given to determining BEN status prior to initiating clozapine. Moreover, adoption of current FDA BEN monitoring criteria in the UK may further reduce clozapine discontinuation due to perceived neutropenia as drug toxicity, particularly in treatment-refractory schizophrenia patients.

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120. Benign Ethnic Neutropenia in a Sample of Nigerian Healthy Controls and Clozapine-Treated Schizophrenia Patients With DARC Null Variant

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