About 2%-3% of children with Down syndrome will develop acute lymphocytic leukemia (ALL) or acute myeloid leukemia (AML), according to the National Cancer Institute, rates that are much higher than in the general population.
Research suggests that among children aged 0-4 years with Down syndrome, the standardized incidence ratio (SIR) of AML is 114, compared with other children, Dr. Roberts said. The SIR of ALL is 27 in children aged 1-4 years, she said.
For people with Down syndrome aged 0-60 years, the SIRs are 12 and 13 in AML and ALL, respectively, she said.
In her presentation, Dr. Roberts focused on AML that appears before age 4 years and is preceded by a neonatal preleukemia – transient abnormal myelopoiesis (TAM) – that only occurs in Down syndrome. In most cases, TAM, which occurs with GATA1 mutations, resolves on its own after birth, she said. But in others, the GATA1 mutations continue and cause AML to develop.
Dr. Roberts highlighted her institution's Oxford Down Syndrome Cohort Study and offered an update to a 2013 report (Blood. 2013 Dec 5;122[24]:3908–17). The study recruited 471 neonates with Down syndrome and followed them for up to 4 years: 341 with no GATA1 mutation and 130 (28%) with the mutation. Dr. Roberts called the latter number a "very high frequency."
Of those with the mutation, 7 patients (5%) developed AML at a median age of 16 months. None of those without the mutation developed AML.
Also, among the 130 neonates with the mutation, 42% were considered to have "clinical" TAM (more than 10% blasts) and 58% were considered to have "silent" TAM (fewer than 10% blasts).
"We predicted that these babies with clinical TAM would have more severe clinical disease ... and that in fact turned out to be the case," Dr. Roberts said.
Why is the GATA1 mutation so significant? Research suggests that platelet production is abnormal in neonates with Down syndrome, compared with neonates without it, regardless of whether they have the mutation, Dr. Roberts said.
The mutation doesn't reduce further platelet count, but does disrupt megakaryopoiesis – the process of the production of platelets. As a result, giant platelets and megakaryocyte fragments are more common, she explained.
Moving forward, research data can be used to identify which children are most at risk, Dr. Roberts said. Newborns with Down syndrome are more likely to survive without leukemia if they have silent TAM, compared with those who have clinical TAM, and if they have an estimated variant allele frequency above 15%, according to findings from the Oxford study.
Children at high risk of AML before age 4 years can be identified by analyzing the percentage of blasts on a smear and/or by analyzing mutation of GATA1, according to Dr. Roberts. However, this cannot be accomplished by the use of a complete blood count (CBC) test, she said, which is used to check for leukemia.
Dr. Roberts called for the development of more guidelines for screening newborns with Down syndrome for leukemia risk. The British Society for Haematology issued testing guidelines, coauthored by Dr. Roberts, in 2018 (Br J Haematol. 2018 Jul;182[2]:200-11).
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