We report a case of familial, chronic, benign neutropenia in a 17-year-old female showing (1) the spontaneous expression of a heritable rare fragile site at 16q22 and (2) a deletion at the same region. The del(16)(q22), which most likely originated from the fragile site, was the main clonal abnormality detected in the patient's bone marrow cells, whereas a few cells with either del(16)(q22) or fra(16)(q22) were seen in the patient's peripheral blood. Interestingly, the del(16q) was also detected in the patient's uncultured cells, as demonstrated by FISH, excluding an in vitro origin of the del(16q) during culture. The bone marrow was hypocellular with decreased neutrophils and their precursors. Absolute neutrophil counts ranged from (0.62 to 1.24) x 10(9)/L with a median value of 1.02 x 10(9)/L. The patient had a more severe neutropenia than her mother, which correlated with the presence of more cells with del(16q) in the marrow. The patient's mother, who was also diagnosed with neutropenia, revealed only a few cells with the rare fra(16)(q22) in her peripheral blood cells, whereas her bone marrow showed cells with both fra(16)(q22) and del(16)(q22), although the del(16q) was present in only 2/20 cells. Some possible candidate genes contributing to the pathogenesis of the neutropenia are discussed. Chromosome abnormalities involving the 16q22 breakpoint have been observed in myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). In this patient, the del(16)(q22) risk factor is unknown for subsequent development of MDS or AML. Another point to consider is the need to determine the origin of a chromosome abnormality, particularly when the clinical picture does not fit the chromosome findings. Although, the observation of a constitutional structural abnormality in a mosaic form is an extremely rare event, it is somewhat different in the case of a fragile site expression, which can, as in this case, be present in some cells and not in others.
Copyright 2006 Wiley-Liss, Inc.