Incidence of monoclonal B-cell disease in siblings of patients with multiple myeloma.

We observed clustering of monoclonal B-cell disease in siblings being screened as allogeneic donors for patients with multiple myeloma (MM) scheduled for stem cell transplantation (SCT). Of 134 asymptomatic donors, the incidence of monoclonal B-cell disease was 8/84 in siblings and 1/50 in matched unrelated donors. From an analysis of five MM families scheduled for allogeneic SCT, monoclonal B-cell disease was detected in 8/27 siblings.