Patterns of monoclonal gammopathy of undetermined significance and multiple myeloma in various ethnic/racial groups: support for genetic factors in pathogenesis.

Monoclonal gammopathy of undetermined significance (MGUS) is one of the most common premalignant disorders in Western countries. Recent studies show that almost every multiple myeloma (MM) case is preceded by an MGUS stage. Interestingly, prevalence and incidence patterns for MGUS and MM show striking disparity patterns across ethnic/racial groups, most notably the two- to threefold increase in both these disorders in African Americans compared with Caucasians. In contrast, studies on Asian patients show lower prevalence/incidence for MGUS/MM compared with Caucasians. Familial aggregation for both MGUS and MM has been observed; the risk for MGUS or MM in family members with these disorders is increased about two- to three fold compared with the general population. Although underlying mechanisms remain unclear, there is evidence of heterogeneity among MGUS patients from different ethnic/racial groups. For example, compared with Caucasians, African-American and African MGUS patients have reportedly lower rates of immunoglobulin M (IgM) MGUS (versus IgG/IgA MGUS) and higher rates of unquantifiable immunoglobulins (Igs). This review focuses on racial disparity and familial aggregation patterns for MGUS and MM and discusses how these observations provide novel clues with regard to pathogenesis.