Monoclonal gammopathies in the adult population of Finistère, France.

Three hundred and thirty-four monoclonal gammopathies were detected in the sera of 30 279 adults from Finistère. Monoclonal gammopathies (MG) are more common in Finistère than in Paris and their distribution is not homogeneous. IgG paraproteins are particularly common in the northeast of Finistère whereas IgM paraproteins are more common in the southwest. Family studies and the high degree of inbreeding would support the hypothesis that there is a genetic predisposition to develop MG but the occurrence of paraproteins among three non-consanguineous couples seems to favour the existence of an environmental factor.