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Diagnosing juvenile myelomonocytic leukemia (JMML) usually involves ruling out other similar diseases such as chronic myelomonocytic leukemia and chronic myeloid leukemia, especially if your child is older than 6 years. Doctors commonly use blood tests and bone marrow tests to diagnose JMML.

The tests used to diagnose JMML include:

  • Blood tests
  • Bone marrow aspiration and biopsy
  • Cytogenetic and molecular tests that look for cytogenetic (chromosomal) and molecular abnormalities (gene mutations) in the cancer cells

Diagnostic Criteria for JMML

Category 1 (All of the following)

  • Presence of an enlarged spleen
  • A persistent elevated monocyte count in the blood (greater than 1x109/L which is equivalent to 1,000 monocytes per microliter of blood (1,000/┬Ál)
  • The absence of the Philadelphia chromosome (Ph chromosome) and the BCR-ABL1 gene rearrangement. The Ph chromosome is an abnormality of chromosome 22 found in the marrow and blood cells of patients with CML
  • Less than 20 percent blasts circulating in the blood and present in the bone marrow

Category 2 (at least one of the following) 

  • Somatic (change in DNA that happens after conception) mutation in PTPN11, KRAS or NRAS genes
  • Clinical diagnosis of neurofribromatosis type 1 (NF1) or NF1 gene mutation 
  • Germline CBL gene mutation

Category 3 (if criteria from category 2 are not met, two of the following are acceptable)

  • Monosomy 7 (only one chromosome from a pair) or any other chromosomal abnormality
  • Higher levels of hemoglobin F than is normal for the age of the patient
  • Myeloid precursors (predecessor of red blood cells, platelets and some types of white blood cells) in the blood
  • Granulocyte-macrophage colony-stimulating factor (GM-CSF) hypersensitivity in colony assay
  • Hyperphosphorylation of STAT5

Cytogenetic (chromosomal) and Molecular Abnormalities

Nearly all JMML patients have an abnormality in a specific gene or chromosome. A mutation in the genes of the RAS pathway is detected in more than 95% of JMML patients. Monosomy 7 and other chromosome 7 abnormalities occur in approximately 25 to 30 percent of patients. See the booklet linked below form more information on these abnormalities. 

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