A Clinical Case of Neonatal Alloimmune Neutropenia

Background: Congenital neutropenia is a common problem in neonates and has myriad etiologies. Neonatal alloimmune neutropenia (NAIN) is among the most common causes of congenital neutropenia with an incidence of 2 per 1000 live births and has an excellent prognosis. NAIN is defined by maternally produced IgG antibodies directed against paternal and fetal neutrophil antigens, most commonly HNA-1a, HNA-1b, and HNA-2a. Case: A 3-week-old female presented with omphalitis and was found to have an absolute neutrophil count (ANC) count of 0. Once admitted and started on IV antibiotics, serial CBC monitoring revealed persistence of neutropenia with ANC counts < 300. On hospital day 3, she was started empirically on subcutaneous filgrastim (GCSF) 5 mcg/kg. Due to a modest response in her ANC, the filgrastim dose was subsequently increased to a max of 30mcg/kg before discharge. Evaluations for etiologies of neutropenia included antineutrophil antibody testing, genetic testing for severe congenital neutropenia (SCN), and a bone marrow exam. SCN was the initial, provisional diagnosis. However, the bone marrow aspiration revealed marked granulocytic hyperplasia with large clusters of promyelocytes, myelocytes, and metamyelocytes and a maturation arrest at the myelocyte – metamyelocyte stage. Antibody neutrophil antibody testing was positive for the HNA-1b antibody, whereas the genetic screen for SCN did not reveal pathogenic mutations. Therefore, she was diagnosed with NAIN and was subsequently weaned off GCSF with a normal ANC. Conclusion: This case illustrates an unusual presentation of NAIN and demonstrates the clinical heterogeneity of this disease state.