Prevalence of monoclonal gammopathy of undetermined significance: study of 52,802 persons in Nagasaki City, Japan.

OBJECTIVE: To assess the prevalence of monoclonal gammopathy of undetermined significance (MGUS) in a large Japanese population. PARTICIPANTS AND METHODS: From October 1, 1988, to March 31, 2004, a total of 52,802 (of 71,675) Japanese survivors of the atomic bomb explosion in Nagasaki City, Japan, were screened for M protein. The youngest participant was 42.3 years as of October 1, 1988. A 2-step screening was performed with a serum protein electrophoresis followed by immunoelectrophoresis and a quantitative determination of serum concentration of immunoglobulins. Twenty-one patients who were diagnosed for the first time at the time of screening as having multiple myeloma and Waldenström macroglobulinemia were excluded from analyses. Age- and sex-specific prevalence rates of MGUS were calculated.
RESULTS: Monoclonal gammopathy of undetermined significance was identified in 1088 of the 52,781 study participants. The overall prevalence of MGUS was 2.1% (95% confidence interval [CI], 1.9%-2.2%) in the total population screened and 2.4% (95% CI, 2.0%-2.6%) in those 50 years or older. The prevalence was significantly higher in men than in women (2.8% vs 1.6%; age-adjusted odds ratio, 2.0; 95% CI, 1.8-2.3; P less than .001). In both sexes, the prevalence rose with increasing age from 1.0% in participants aged 42 to 49 years, 1.9% in those 50 to 59 years, 2.6% in those 60 to 69 years, and 3.0% in those 70 to 79 years, to 4.4% in those 80 years and older. The heavy chain isotypes of immunoglobulin were IgG in 73.6% of patients, IgA in 17.7%, IgM in 7.5%, and oligoclonal gammopathies in 1.1%.
CONCLUSION: The prevalence of MGUS is lower in this Japanese population than that reported in Western countries among people older than 60 years, especially among women.