Distinct chromosome 3 abnormalities in persistent polyclonal B-cell lymphocytosis

Persistent polyclonal B-cell lymphocytosis (PPBL) is a rare entity of unkno wn etiology characterized by a polyclonal expansion of B-lymphocytes with t ypical bilobulated forms, elevated serum IgM, and an additional isochromoso me for the long arm of chromosome 3 as the sole change. In the present stud y, we investigated four cases of PPBL by means of conventional cytogenetic analysis and FISH. In all patients, the polyclonality of the lymphoprolifer ation was demonstrated by immunophenotypic studies, and PCR analysis failed to demonstrate clonal IGH rearrangements in three evaluated cases. In two patients, in addition to +i(3)(q10), banding techniques identified unrelate d clones with trisomy 3. FISH studies using a chromosome 3 long arm-specifi c probe provided evidence that all cases had both +i(3)(q10) and +3. To det ermine more precisely the distribution of the chromosomal abnormalities wit hin the peripheral lymphocyte population, we investigated two of these case s using a technique of simultaneous fluorescence immunophenotyping and inte rphase cytogenetics (FICTION). We demonstrated that both abnormalities were randomly distributed among the B-lymphocytes, independently of the kappa o r lambda light chain isotype and the nuclear aspect. These data lead us to conclude that trisomy 3 represents, in addition to +i(3)(q10), another recu rrent cytogenetic change in PPBL, suggesting that this lymphoproliferative disorder is associated with an increased frequency of chromosome 3 instabil ity. (C) 1999 Wiley-Liss, Inc.