Down syndrome (also referred to as Down’s syndrome) is a common genetic disorder that occurs in about 1 of every 700 births. It occurs when a child is born with an extra chromosome (DNA molecule). Although Down syndrome and leukemia (blood cancer) may appear unrelated, there is a connection between the two. Children born with Down syndrome are at an increased risk of developing acute leukemia.
It’s important to explore the connections between leukemia and Down syndrome, including how both conditions are managed. As always, a health care provider is the best resource if leukemia and Down syndrome are suspected.
Each cell in the human body contains genetic information that codes for our inherited traits. This information is carried along rod-like structures called chromosomes. Typically, a person inherits 23 chromosomes from each parent (46 total).
Down syndrome is a genetic condition in which a person has an extra chromosome at position 21 (or, more rarely, at positions 13 or 18), leading to a total of 47 chromosomes. This genetic change arises during the first stages of development — in most cases, just before or at conception (fertilization).
Trisomy 21 is the most common form of Down syndrome, accounting for 95 percent of cases. This form of the condition occurs due to an error in cell division known as disjunction, which results in an embryo (early stage of development) that has an extra copy of chromosome 21.
There are two other types of Down syndrome: translocation Down syndrome and mosaic Down syndrome. The former occurs when an extra chromosome 21, or part of the chromosome, is present, but it has been “translocated” to a different chromosome (rather than existing as a separate chromosome 21). Mosaic Down syndrome occurs when some of a baby’s cells have an extra (third) copy of chromosome 21, while others have the usual two copies.
The extra genetic material present in babies with Down syndrome affects their development while in the womb. This causes the physical and cognitive (mental) characteristics seen in people with Down syndrome. This genetic change is also responsible for an increased risk of developing numerous health problems, including leukemia.
Children born with Down syndrome have a significantly higher risk of having childhood leukemia. Those with trisomy 21, in particular, are much more likely to develop acute lymphocytic leukemia (ALL) and acute megakaryoblastic leukemia (AMKL, a type of acute myeloid leukemia) than those without Down syndrome.
It has also been found that a type of pre-leukemia known as transient leukemia (transient myeloproliferative disorder, or TMD) affects up to 30 percent of newborn babies with Down syndrome. In most cases, this condition goes away on its own within the first month of life, often without treatment. However, in about one quarter of cases, children with TMD will go on to develop AMKL or another disorder known as myelodysplastic syndrome (MDS), a form of myeloid leukemia in Down syndrome (ML-DS).
Leukemogenesis (the production or induction of leukemia) of AMKL in children with Down syndrome has been associated with genetic abnormalities involving the GATA1 gene. Mutations in this gene result in a shorter GATA1 protein than usual, which leads to the uncontrolled proliferation of immature megakaryocytes (large bone marrow cells). It is believed that trisomy 21 (having an extra copy of the chromosome at position 21) likely plays a role in the development of GATA1 mutations in children with Down syndrome.
Researchers continue to explore the connections between TMD and ML-DS, as well as those between pre-leukemia, leukemia, and Down syndrome. Studying how early fetal development promotes leukemogenesis could help them better understand the origins of Down syndrome-related leukemia and identify new, more successful treatments.
The cure rate for leukemia in children with Down syndrome is exceptionally high. Research has found that those with acute myeloid leukemia (AML) — and, in particular, AMKL — have survival rates ranging from 80 percent to 100 percent. It is believed that the genetic mutation that causes leukemia in children with Down syndrome also allows them to respond better to a certain type of chemotherapy.
That said, the outcomes of children with Down syndrome and acute lymphoblastic leukemia have been reported to be slightly less successful than those without Down syndrome (60 percent to 70 percent, compared to 75 percent to 85 percent in the general population). This has been attributed to the fact that children with Down syndrome and leukemia are more prone to infections and are more likely to experience significant toxicity (ill effects) as a result of chemotherapy — particularly, the drug methotrexate, which is used to treat acute lymphoblastic leukemia.
Cancer doctors (hematologists or oncologists) can adjust the chemotherapy regimen for people with Down syndrome to account for their increased sensitivity to the treatment. An oncology expert will help them get the most significant benefits from their treatment while minimizing negative side effects.
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