Some genes control when our cells grow, divide into new cells, and die at the right time.
Certain genes that help cells grow, divide, or stay alive are called oncogenes. Others that
slow down cell division or cause cells to die at the right time are called tumor suppressor
genes.
Cancers can be caused by DNA mutations (or other types of changes) that turn on
oncogenes or turn off tumor suppressor genes. These gene changes can be inherited from
a parent (as is sometimes the case with childhood leukemias), or they may happen
randomly during a person’s lifetime if cells in the body make mistakes as they divide to
make new cells.
A common type of DNA change that can lead to leukemia is known as a chromosome
translocation. Human DNA is packaged in 23 pairs of chromosomes. In a translocation,
DNA from one chromosome breaks off and becomes attached to a different chromosome.
The point on the chromosome where the break occurs can affect oncogenes or tumor
suppressor genes. For example, a translocation seen in nearly all cases of childhood
chronic myeloid leukemia (CML) and in some cases of childhood acute lymphocytic
leukemia (ALL) is a swapping of DNA between chromosomes 9 and 22, which leads to
what is known as the Philadelphia chromosome. This creates an oncogene known as
BCR-ABL. Many other changes in chromosomes or in specific genes have been found in
childhood leukemias as well.
Some children inherit DNA mutations from a parent that increase their risk for cancer
(see the section “What are the risk factors for childhood leukemia?”). For instance, a
condition called Li-Fraumeni syndrome, which results from an inherited mutation of the
TP53 tumor suppressor gene, increases a person’s risk of developing leukemia, as well as
some other cancers.
Certain inherited diseases can increase the risk of developing leukemia, but most
childhood leukemias do not seem to be caused by inherited mutations. Usually, DNA
mutations related to leukemia develop after conception rather than having been inherited.
Some of these acquired mutations might occur early, even before birth. In rare cases,
acquired mutations can result from exposure to radiation or cancer-causing chemicals, but
most often they occur for no apparent reason.
A few studies have suggested that some childhood leukemias may be caused by a
combination of genetic and environmental factors. For example, certain genes normally
control how our bodies break down and get rid of harmful chemicals. Some people have
different versions of these genes that make them less effective. Children who inherit these
genes may not be as able to break down harmful chemicals if they are exposed to them.
The combination of genetics and exposure might increase their risk for leukemia.