Most MM secrete a complete or incomplete (light chains (LC) only) monoclonal immunoglobulin (IgG > LC > IgA >  > IgM, IgD, IgE), but a very small subset of non-secretory MM lacks a detectable M-protein in blood or urine, even if very sensitive tests such as the free light chain ratio are used. This evidence concerns the gene IGHE and Miyoshi myopathy.