Neonatal Immune Neutropenia due to Isoantibodies against the Granulocyte Receptor FcγRIIIb.

INTRODUCTION: Neonatal neutropenia is often secondary to sepsis, low birth weight, pregnancy-induced maternal hypertension, and other conditions. CASE REPORT: We report a case of asymptomatic isoimmune neutropenia in a pair of preterm twins. Genotyping confirmed that the mother was negative for HNA-1a, 1b, and 1c, consistent with an FcγRIIIb deficiency. The father was 1(a+b+c-) and the neonates were 1(a-b+c-). A strongly positive result was observed in the granulocyte immunofluorescence test against paternal neutrophils (IgG antibodies). IgG anti-CD16b isoantibodies were detected in the mother's breast milk. Neutropenia resolved after 28 days without requiring any specific treatments. DISCUSSION: Even though neonatal alloimmune neutropenia (NAN) is usually benign and self-limiting, some patients pre-sent with delayed separation of the umbilical cord, mild skin infections, omphalitis, or severe infections like pneumonia, sepsis, and meningitis. Thus, it is important to rule out NAN in case of neonatal neutropenia.