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RAS-associated autoimmune lymphoproliferative disorder (RALD) is a nonmalignant syndrome characterized by lymphadenopathy, splenomegaly, increases in B-lymphocytes and monocytes, hypergammaglobulinemia, and autoimmunity. It can simulate the clinical picture of juvenile and chronic myelomonocytic leukemia (JMML/CMML). Activating mutations are observed in KRAS or NRAS in myeloid and lymphoid lineages and are identical to the RAS mutations observed in up to 25% of patients with JMML.
To differentiate RALD from JMML/CMML, investigators studied 13 RALD patients (age, 5 to 57 years) with RAS mutations; all but one had disease onset before age 6. In these patients, the mean absolute monocyte count was 2700 per μL (range, 1500–9910), many of the mon…