Emergence of an unusual bone marrow precursor B-cell population in fatal Shwachman-Siamond syndrome

The Shwachman-Diamond syndrome (SDS) is a rare congenital disorder for whic h inheritance by an autosomal recessive trait has been suggested. Shwachman -Diamond syndrome is defined by exocrine pancreatic insufficiency combined with severe neutropenia. Moreover, SDS patients are at risk to develop neop lastic hematologic diseases. We describe 2 SDS-affected daughters of consan guine parents who were born 1 year apart, at 35 and 36 weeks of gestation, and who died at the age of 4 and 3.5 months, respectively, due to respirato ry infections. Histologic bone marrow evaluation of the second-born child r evealed a diffuse proliferation of immature B cells, which comprised 40% of the total cellularity. These cells were identified as precursor B cells by immunophenotyping studies (CD79a(+)/CD10(+)/CD20(-)/CD22(-)/CD34(-)/termin al deoxynucleotidyl transferase(-)). Molecular determination of the immunog lobulin heavy-chain gene status did not reveal clonality. The emergence of this peculiar B-cell population was interpreted as a marked increase of hem atogones. Although the clinical significance and the exact function of hema togones is still obscure, they may play a critical regenerative role in the regulation of hemopoiesis, but without malignant potential in SDS. Immunop henotyping and molecular studies, therefore, have potential value in the di fferential diagnosis of primary bone marrow failures. This report adds SDS to the spectrum of conditions in which a prominent number of hematogones ma y be observed.