The specific cause for most leukemias in children is unknown, but there are a few known risk factors related to this type of cancer. These include genetic disorders, such as Down syndrome (trisomy 21) and Li-Fraumeni syndrome; inherited immune system conditions, such as Ataxia-telangiectasia and Wiskott-Aldrich syndrome and environmental risk factors, like exposure to radiation or chemotherapy given for other cancers.