The NA"null" phenotype of a young man is caused by an Fc gammaRIIIB gene deficiency while the products of the neighboring Fc gammaRIIA and Fc gammaRIIIA genes are present.

A 27-year-old man with an allergy to house dust mites was found to lack the Fc gammaRIIIb on his neutrophils. Cell surface marker and PCR techniques were used to investigate possible reasons for this deficiency. Agglutination and immunofluorescence assays using the man's neutrophils together with NA1- and NA2-specific antibodies were negative, and there was no reaction with the Fc gammaRIII-specific mAb 3G8. Indirect immunofluorescence demonstrated the presence of the CD24 molecule, which, like the Fc gammaRIIIb, is anchored to the cell membrane by glycosylphosphatidylinositol. Thus a lack of the Fc gammaRIIIb cell membrane anchor was excluded. PCR analysis confirmed the absence of the NA1 and NA2 alleles. The individual was therefore typed as NA"null". The products of those genes located together with the Fc gammaRIIIB gene within a complex on chromosome 1 (q23-24) were examined. Fc gammaRII was demonstrated on monocytes and B cells with the use of Fc gammaRII-specific monoclonal antibodies. About 5% of the individual's peripheral blood monocytes were positive with the 3G8 antibody, indicating the presence of Fc gammaRIIIa. From these data we concluded that the Fc gammaRIIIb deficiency on the neutrophil cell surface of this individual is due to a lack of the Fc gammaRIIIB gene while excluding a lack of the Fc gammaRIIA and the Fc gammaRIIIA genes.