Juvenile myelomonocytic leukemia (JMML) is a serious chronic leukemia (cancer of the blood) that affects children mostly aged 4 and younger. The name JMML now encompasses all diagnoses formerly referred to as juvenile chronic myeloid leukemia (JCML), chronic myelomonocytic leukemia of infancy, and infantile monosomy 7 syndrome. The average age of patients at diagnosis is 2 years old. The World Health Organization has included JMML in the category of myelodysplastic and myeloproliferative disorders. Signs and symptoms The following symptoms are typical ones which lead to testing for JMML, though children with JMML may exhibit any combination of them: pallor, fever, infection, bleeding, cough, poor weight gain, a maculopapular rash (discolored but not raised, or small and raised but not containing pus), lymphadenopathy (enlarged lymph nodes), moderate hepatomegaly (enlarged liver), marked splenomegaly (enlarged spleen), leukocytosis (high white blood cell count in blood), absolute monocytosis (high monocyte count in blood), anemia (low red blood cell count in blood), and thrombocytopenia (low platelet count in blood). Most of these conditions are common, nonspecific signs and symptoms. Children with JMML and neurofibromatosis 1 (NF1) (about 14% of children with JMML are also clinically diagnosed with NF1, though up to 30% carry the NF1 gene mutation) may also exhibit any of the following symptoms associated with NF1 (in general, only young children with NF1 are at an increased risk of developing JMML): 6 or more café-au-lait (flat, coffee-colored) spots on the skin 2 or more neurofibromas (pea-size bumps that are noncancerous tumors) on or under the skin Plexiform neurofibromas (larger areas on skin that appear swollen) Optic glioma (a tumor on the optic nerve that affects vision) Freckles under the arms or in the groin 2 or more Lisch nodules (tiny tan or brown-colored spots on the iris of the eye) Various bone deformations including bowing of the legs below the knee, scoliosis, or thinning of the shin bone Noonan syndrome (NS) may predispose to the development of JMML or a myeloproliferative disorder (MPD) associated with NS (MPD/NS) which resembles JMML in the first weeks of life. However, MPD/NS may resolve without treatment. Children with JMML and Noonan's syndrome may also exhibit any of the following most-common symptoms associated with Noonan's syndrome: Congenital heart defects, in particular, pulmonic stenosis (a narrowing of the valve from the heart to the lungs) Undescended testicles in males Excess skin and low hair line on back of neck Widely