Increased incidence of monoclonal gammopathy of undetermined significance in blacks and its age-related differences with whites on the basis of a study of 397 men and one woman in a hospital setting.

Serum samples from 398 individuals (270 whites and 128 blacks) exhibiting quantitatively normal amounts of five typically seen fractions (albumin, alpha 1-globulin, alpha 2-globulin, beta-globulin, and gamma-globulin) in serum protein electrophoresis and showing no evidence of multiple myeloma, other immunoproliferative diseases, or any of the other diseases known to produce monoclonal proteins were tested for monoclonal gammopathy of undetermined significance (MGUS) by immunofixation electrophoresis. No individual in the study had a serum protein electrophoresis pattern suggestive of monoclonal protein gammopathy. Except for one 37-year-old woman, all subjects were men. Subjects were divided into seven age groups: 20 to 29 years (I), 30 to 39 years (II), 40 to 49 years (III), 50 to 59 years (IV), 60 to 69 years (V), 70 to 79 years (VI), and all over 79 years (VII) of age. Considering all subjects in a given race, blacks had two times (14.8%) higher incidence of MGUS than whites (7.8%); this difference was statistically significant. An increased incidence of MGUS in blacks when compared with whites prevailed in each age group, and the difference was statistically significant in all age groups except group II. No MGUS was found in groups I and III in either race. Both races showed a threefold increase in incidence of MGUS from group II to group VII. No routine laboratory test such as erythrocyte sedimentation rate in subjects with MGUS was significantly different than that in age- and race-matched individuals without MGUS. These results show that the incidence of MGUS is higher in the group (blacks) also known to have a higher prevalence of multiple myeloma.