Center for Research on Genomics and Global Health, National Human Genome Research Institute, National Institutes of Health (NIH), Bethesda, Maryland, United States of America.
Molecular and Clinical Hematology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, Maryland, United States of America.
PLoS One. 2018 Mar 29;13(3):e0194400. doi: 10.1371/journal.pone.0194400. eCollection 2018.
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.
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.
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).
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.
良性种族中性粒细胞减少症（BEN）是一种与非裔和特定中东族群有关的血液学病症。先前在大型人群中的遗传关联研究表明，趋化因子的达菲抗原受体（DARC）基因中的 rs2814778 与 BEN 相关，特别是 DARC 无效红细胞表型。然而，导致白细胞计数低的这种红细胞表型的机制仍不清楚。
我们进行了一项极端表型设计的全基因组关联研究（GWAS），对来自地理和种族差异中风原因（REGARDS）研究的 1178 名非裔美国人个体中的约 1600 万个单核苷酸多态性（SNP）进行了分析，并在动脉粥样硬化风险社区（ARIC）研究中的 819 名非裔美国人参与者中进行了复制。对 rs2814778 进行条件分析，以确定染色体 1q22 上的其他关联信号。在一个有和没有 BEN 的健康个体的独立队列中，分析外周血中性粒细胞的全基因组基因表达。
我们证实，DARC 中的 rs2814778 与 BEN 相关（p=4.09×10-53）。在 rs2814778 Conditioning 条件下，其他染色体 1 关联信号被消除。霍华德大学家庭研究（HUFS）和动脉粥样硬化多民族研究（MESA）中的参与者的炎症细胞因子（IL-2、6 和 10）在与 rs2814778 等位基因纯合的个体中的水平与其他个体相似，表明细胞因子吸收假说在白细胞稳态中发挥的作用较小。有和没有 BEN 的个体的中性粒细胞基因表达也相似，除了 BEN 中的低 DARC 表达外，表明其正常功能。BEN 中性粒细胞在白细胞迁移和造血干细胞动员途径中具有略微激活的特征（表达倍数变化<2）。
这些人类研究结果支持 DARC 无效的红细胞祖细胞优先分化为髓样细胞的观点，导致从循环中激活的 DARC 无效中性粒细胞进入脾脏，并导致相对中性粒细胞减少症。总的来说，这些人类数据充分解释了 DARC 无效红细胞表型导致 BEN 的机制，并进一步提供了一个生物学基础，即 BEN 在临床上是良性的。
