Isoimmune neonatal neutropenia caused by Fc gamma RIIIb antibodies in a Spanish child.
BACKGROUND: Fc gamma RIIIb deficiency is a rare defect in which neutrophils do not express Fc gamma RIIIb and therefore the individuals with this defect have an NA null phenotype. Soluble Fc gamma RIII in plasma is severely decreased and almost undetectable. During pregnancy, Fc gamma RIIIb deficiency may cause the formation of maternal Fc gamma RIIIb antibodies, which leads to an isoimmune neonatal neutropenia. The first known case of isoimmune neonatal neutropenia caused by these antibodies in a Spanish child was identified. CASE REPORT: A newborn infant was severely affected by omphalitis; analysis of his blood showed an absolute neutropenia, but he responded well on intravenous immunoglobulin therapy. The maternal antiserum reacted strongly with all tested Fc gamma RIIIb-positive neutrophils. A family study showed that the infant's mother, one of the mother's sisters, and her mother were Fc gamma RIIIb deficient. No neutrophil antibodies were found in the plasma from these other Fc gamma RIIIb-negative women, although both had had numerous pregnancies. The three women were healthy, but one had recurrent otitis. DNA analysis of the family showed the absence of both Fc gamma RIIIB genes in the three Fc gamma RIIIb-negative women. The father of the child and all the children of the Fc gamma RIIIB gene-deficient women were shown to lack one of the Fc gamma RIIIB genes. CONCLUSION: A new case of isoimmune neonatal neutropenia caused by anti-Fc gamma RIIIb is identified. The family study indicates that the Fc gamma RIIIb deficiency is a hereditary genetic defect. In accordance with the location of Fc gamma RIIIB on chromosome 1, an autosomal pattern of inheritance of the Fc gamma RIIIB-deficient allele was observed.