Leukemia is the most common type of cancer in children and adolescents. Little is known about how the disease is caused, but previous studies have indicated a link between leukemia and maternal infections. A new study of Danish children has shed more light on the topic.
Leukemias are a group of cancers that affect the blood cells, preventing them from developing into specific types of cells. Most childhood leukemias are acute, meaning they progress quickly and, if not treated, can be fatal.
Typically, leukemia affects the production of white blood cells, which are part of the body’s immune system and fight infection and other diseases. The most common type of childhood leukemia is acute lymphoblastic leukemia (ALL), accounting for 75% of cases of leukemia in children and adolescents. ALL causes the bone marrow to overproduce immature versions of white blood cells called lymphoblasts, and children with ALL are prone to anemia and recurrent infections and bleed and bruise more easily.
Acute myeloid leukemia (AML) affects the myeloid cells, which are responsible for producing myeloblasts, an immature version of white blood cells, as well as red blood cells and platelets. In AML, myeloblasts are overproduced, collecting in the bone marrow and stopping the production of normal blood cells. This can lead to anemia, bleeding and/or bruising. Although it usually occurs in adults, AML accounts for 17% of cases in children and adolescents.
While the signs and symptoms of ALL and AML are fairly similar, diagnosis and treatment are different for each.
A 2019 review of previously published studies found that infection with influenza, rubella (German measles), and varicella (chickenpox) during pregnancy was associated with a higher risk of childhood leukemia. However, some of these studies were found to contain biases.
With these studies in mind, researchers from Denmark and Sweden undertook a long-term study of over 2.2 million Danish children to ascertain the occurrence of childhood leukemia in circumstances of maternal infection during pregnancy. The researchers looked at infections based on where they occurred in the body, including the respiratory tract, urinary and genital tracts, and digestive system.
After adjusting for variables that might influence the data, researchers found that a maternal infection of any source during pregnancy was associated with a 35% increased risk of childhood leukemia. Looking at particular infection sites, the data revealed that infections of the urinary tract and genital tract were associated with a 142% and 65% increased risk, respectively, of childhood leukemia. These results were consistent with a previous Swedish study.
ALL and AML are thought to be caused by different mechanisms that occur before birth. However, the results of the current study suggest that maternal infection is a common factor in both types of the disease.
No association was found between maternal infection and other types of childhood cancer, such as brain tumors or cancer of the lymphatic system (lymphoma).
The researchers recognized that, while the large sample size and the high quality of the data were strengths, the fact that data was obtained from hospital diagnoses meant that milder or undiagnosed infections might not have been captured by the study. Further, data about the treatment mothers received for their infection were unavailable, so researchers could not examine whether treatment affected the risk of childhood leukemia.
Despite these limitations, the research is instructive. Since little is known about the cause of childhood leukemia, the indication that maternal infection contributes to a higher risk of developing the disease will usefully guide future studies, improving understanding of the disease and, potentially, leading to the development of measures to prevent it.
The study was published in JAMA Network Open.
Source: JAMA Network via EurekAlert!
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