Basic research and case-control study (bone marrow biopsy specimens from 15 newly diagnosed multiple myeloma [MM] patients and 8 control as well as primary CD138+ MM cells; Plasma cells from 43 newly diagnosed cases of MM and 18 controls; Human MM cell lines: RPMI8226, ARH-77 and U266). The gene discussed is SDC1; the disease is AL amyloidosis.