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 boneNoonan 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 Noonans syndrome may also exhibit any of the following most-common symptoms associated with Noonans 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 set eyes
Diamond-shaped eyebrows
Ears that are low-set, backward-rotated, thick outer rim
Deeply grooved philtrum (upper lip line)
Learning delays

Genetics
About 90% of JMML patients have some sort of genetic abnormality in their leukemia cells that can be identified with laboratory testing.
Low-dose conventional chemotherapy:  Studies have shown no influence from low-dose conventional chemotherapy on JMML patients’ length of survival. Some combinations of 6-mercaptopurine with other chemotherapy drugs have produced results such as decrease in organ size and increase or normalization of platelet and leukocyte count. Intensive chemotherapy:  Complete remission with ongoing durability from JMML has not been possible through use of intensive chemotherapy, but it is still used at times because it has improved the condition of a small but significant number of JMML patients who do not display an aggressive disease. The COG JMML study administers 2 cycles of fludarabine and cytarabine for 5 consecutive days along with 13-cis retinoic acid during and afterwards. The EWOG-MDS JMML study, however, does not recommend intensive chemotherapy before bone marrow transplant. 13-cis retinoic acid (Isotretinoin):  In the lab, 13-cis-retinoic acid has inhibited the growth of JMML cells. The COG JMML study therefore includes 13-cis-retinoic acid in its treatment protocol, though its therapeutic value for JMML remains controversial. Radiation
Radiation to the spleen does not generally result in a decrease in spleen size or reduction of platelet transfusion requirement. Stem cell transplantation
The only treatment that has resulted in cures for JMML is stem cell transplantation, also known as a bone marrow transplant, with about a 50% survival rate. The risk of relapsing after transplant is high, and has been recorded as high as 50%. Generally, JMML clinical researchers recommend that a patient have a bone marrow transplant scheduled as soon as possible after diagnosis.