Duffy phenotyping and FY*B-67T/C genotyping as screening test for benign constitutional neutropenia

Abstract

Objective Low levels of neutrophils can be an intrinsic condition, with no clinical consequences or immunity impairment. This condition is the benign constitutional neutropenia (BCN), defined as an absolute neutrophils count (ANC) 2000 cells/mm. Diagnosis of BCN is of exclusion where patients are submitted to blood tests and possibly to invasive diagnostic search until secondary causes of neutropenia are ruled out. The natural history of the disease suggests benign evolution and Brazilian study showed an overall frequency of 2.59%. The main mechanisms include reduced neutrophil production, increased marginalization, extravasation to the tissues and immune destruction. Genetic studies showed strong association between the single nucleotide variant rs2814778 located on chromosome 1q23.2 in the promoter region of the atypical chemokine receptor 1 (Duffy blood group system) gene (ACKR1, also termed DARC) and BCN. The aim of this study is to evaluate FY phenotypes and genotypes including the analysis of the rs 2814778 SNP in Brazilian patients with BCN in order to determine an effective diagnostic tool, allowing reassurance of the patient and cost reduction in their care. Methods Case control study, with 94 individuals (18 patients and 76 controls). Phenotyping was performed by gel test and genotyping was performed by PCR-RFLP. Results White blood cell (WBC) and absolute neutrophils (AN) counts showed lower levels in patients compared to controls. In the patient group 83.3% were genotyped as FY*B/FY*B. The SNP rs2814778 (-67T > C) was identified in 77.8% of the patients genotyped as FY*B-67C/FY*B-67C. In the control group, 72.7% were homozygous for the wild type and 23.3% were heterozygous. Conclusion This study reinforces that FY phenotyping and genotyping can be used to detect most people with BCN, avoiding excessive diagnostic investigation. Besides, this procedure may reduce health costs and be reproductible in clinical practice.

Isolated Neutropenia/Benign Ethnic Neutropenia: A Common Clinical and Laboratory Finding in Southern and Western Saudi Arabia

“…Moreover, since molecular analysis for rs2814778 of Duffy-null phenotypes is not available in clinical laboratories, the Duffy phenotype could be utilized as a marker for identifying individuals with BEN. 33 In current clinical practice, the diagnosis of BEN depends on the exclusion of other causes of neutropenia.…”

Absolute neutrophil count by Duffy status among healthy Black and African American adults

“…Lower neutrophil counts were historically linked with African ancestry, but we now know that this lower ANC is strongly associated with a single nucleotide polymorphism residing in the promoter region of the DARC gene that prevents transcription and results in the red blood cell Duffy-null phenotype [Fy(a−b−)]. 6 , 7 The Duffy antigen is postulated to be a cytokine sink that binds to inflammatory cytokines, and therefore, the null form attracts neutrophils into the periphery less readily. 8 Additionally, this single nucleotide polymorphism affects hematopoiesis and results in phenotypically distinct neutrophils that readily leave the periphery.…”

Benign ethnic neutropenia: an analysis of prevalence, timing and identification accuracy in two large inner-city NHS hospitals

“…While most investigators broadly describe BEN prevalence in 25-50% of black people [2], some studies report lower rates in similar populations, even with different geographic regions in the African continent and the middle-east. (However, this is possibly related to the presence of Caucasian heritage in patients classified as "Black" in these studies, resulting in heterozygosity for the ACKR1 genotype) [1,48,49]. Notwithstanding, the proportion of patients identified with BEN in our populations were still less than the lowest commonly reported prevalence rate.…”

“…In instances, they require the help of a biostatistician with expertise in variant calling, as well as other in-silico prediction tools/ software, where it is a variant of uncertain significance. Notwithstanding, Duffy antigen testing provides a quicker and likely less expensive alternative, particularly if implemented into routine practice [46,49].…”