Children with Down syndrome are at substantially increased risk of developing acute leukemias. In particular, a type of acute myeloid leukemia (AML) called
acute megakaryoblastic leukemia is 500+ times more common in young children with Down syndrome than in age-matched control populations. Down syndrome also increases the risk of developing another kind of leukemia called acute lymphoblastic leukemia (ALL) which is also the most common type of childhood malignancy. None of this means that all kids with Down syndrome get leukemia, but the association is clear and has been known since the 1930s. The link between trisomy 21 and leukemia is not fully understood, but a promising candidate is a gene called
RUNX1, which is located on chromosome 21 and regulates the development of blood cells in bone marrow. It appears that having an extra copy of
RUNX1 is at least partly responsible for the increased risk of AML observed in people with Down syndrome.
Something that I find intriguing is that in general, childhood AML has a worse outcome than childhood ALL. Approximately 90% of children diagnosed with ALL will be completely cured by treatment. For all types of childhood AML, however, the 5 year overall survival rate is only about 60%.
Down syndrome associated acute megakaryoblastic leukemia (
DS-AMKL) has a particularly good prognosis, with some studies indicating a 5 year overall survival rate of almost 100%, whereas
less than 50% of children with non-DS AMKL will survive 5 years from diagnosis.