Chromosomal abnormalities in systemic amyloidosis.

Primary systemic amyloidosis (AL) is a plasma cell disorder characterized by deposition of monoclonal light chains in different organ systems. Although multiple and complex numerical chromosomal abnormalities have been described in patients with multiple myeloma, it is currently unknown whether such changes occur in systemic amyloidosis. Bone marrow samples from 21 patients with AL were studied by standard cytogenetics and interphase fluorescence in situ hybridization (FISH) for the presence of numerical chromosomal abnormalities. We tested for six chromosomes (7, 11, 9, 15, 18 and X) using centromere-specific probes. The monoclonal plasma cells were identified by simultaneous fluorescent staining of the monotypic cytoplasmic immunoglobulin. We compared these results with those obtained from 19 patients with monoclonal gammopathy of undetermined significance (MGUS) and normal controls. Multiple numerical chromosomal abnormalities were detected in AL by interphase FISH, including trisomy of chromosomes 7 (42%), 9 (52%), 11 (47%), 15 (39%), 18 (33%) and X (13% in women and 54% in men). Monosomy of chromosome 18 was seen in 72% of cases. Previous exposure to alkylator therapy did not appear to correlate with these abnormalities. No significant difference was observed in the prevalence of these abnormalities between AL and MGUS. Multiple chromosomal numerical abnormalities were detected by interphase FISH analysis in patients with AL, especially monosomy of chromosome 18. Aneuploidy in the monotypic plasma supports a neoplastic nature for the disorder.