CBL and juvenile myelomonocytic leukemia: In addition, 10–15% of JMML patients show clinical signs of neurofibromatosis with biallelic inactivation of the NF1 locus in leukemic cells7, and another 10–15% have an underlying developmental disorder with germline CBL mutations (herein termed “CBL syndrome”) and acquired loss of heterozygosity at the locus in leukemic cells5,8.