free κ/λ or λ/κ light chain ratio) less than 100, providing that the higher light chain concentration is >100 milligram/liter; and e) a circulating blood plasma cell absolute count of <2x109 and/or <20% of total circulating nucleated cells. Presence of any one of the latter findings indicates that the plasma cell dyscrasia has progressed beyond the MGUS stage.Non-IgM MGUS is a relatively stable condition afflicting 3% of people aged 50 and 5% of people aged 70; on average, it progresses to multiple myeloma at a rate of 0.5-1% cases per year, as defined in studies following patients over a 25-year period. A study conducted by the Mayo Clinic found that MGUS associated with non-IgG myeloma proteins or with serum myeloma protein levels greater than 15 gram/liter had a greater risk per year of progression to multiple myeloma. A Spanish study group found that MGUS patients demonstrating aneuploidy (i.e. abnormal number of chromosomes) in bone marrow cells or >95% of resident bone marrow plasma cells that are clonal in nature also have a greater risk per year of progression to myeloma. In a more recent study, MGUS patients that had the presence of none, 1, 2, or 3 of the three following risk factors, serum M protein levels >15 gram/liter, a non-IgG isotype, and abnormal free light chain ratios, had 5, 32, 37, and 58% chances, respectively, of progressing to multiple myeloma within 20 years.
Heavy chain disease
The four heavy chain diseases are exceedingly rare conditions associated with the production, circulation in blood, and often presence in urine of  a free clonal heavy chain with no detected clonal light chains. The heavy chain is non-functional and altered by having deletions, insertions, and point mutations due to somatic mutations in their respective coding genes. Beyond this commonality, however, these diseases have very different clinical differences. Furthermore, each of the heavy chain diseases appears to be due to rare variants of lymphoma and therefore is sometimes regarded as a B cell dyscrasia However, heavy chain diseases are still often classified with plasma cell dyscrasias. The heavy chain diseases are classified as α, γ, and μ heavy chain diseases and are based respectively on >400, 130, and 30-40 case reports as reviewed in a 2014 publication. α Heavy chain disease
α Heavy chain disease (also termed immunoproliferative small intestinal disease or IPSID, Mediterranean lymphoma, and Seligmann disease) afflicts primarily individuals of  Mediterranean, North African, and Middle Eastern descent of lower economic status. Many cases are centered in the Middle East and associated with relatively unsanitary living conditions. The disease usually appears between the ages 10 and 30 and in some cases may be an aberrant immune response to a parasite or other microorganism. The disease commonly effects the gastrointestinal tract leading to signs and symptoms of a malabsorption syndrome or, far less commonly, the respiratory tract with signs and symptoms of respiratory dysfunction.