It has also been shown to correlate with B cell biomarkers of disease activity such as beta-2 microglobulin, serum free light chains of immunoglobulins, the cytokine BAFF and FMS-like tyrosine kinase 3 ligand levels, as well as with cytopenias, hypocomplementemia and cryoglobulinemia [33–36]. The gene discussed is FLT3; the disease is cryoglobulinemia.