The exact cause of acute lymphocytic leukemia (ALL) in children has not been identified. Researchers, however, have gained a greater understanding of how specific changes in DNA can cause bone marrow stem cells to develop into leukemia.

Some forms of cancer are caused by DNA mutations that “turn on” oncogenes (genes that speed up cell division) or “turn off” tumor suppressor genes (genes that slow down cell division or cause cells to die at the right time). In children with leukemia, these mutations are normally acquired after birth. Some of these mutations, such as those caused by exposure to radiation, can occur in developing fetuses and are already present at birth. 

One form of DNA abnormality that can cause leukemia to develop is a translocation. A translocation is the transfer of DNA from one chromosome to another. This abnormality can turn on oncogenes which causes rapid cell division. 

In addition, researchers have identified a number of factors that may make a child more likely to develop ALL. These risk factors include:

• Chemotherapy. Children treated with certain chemotherapy drugs, including alkylating agents, are at an increased risk of developing ALL later in life. Typically the leukemia develops five to ten years after treatment, and is difficult to treat.
  
  
• Down syndrome. Children with this condition have an extra copy of chromosome 21. Having this disorder makes a child 15 times more likely to develop ALL than the average child.
  
  
• Having a sibling with leukemia. A child with an identical twin who develops ALL before 6 years of age has a 20 to 25 percent chance of developing leukemia.  Fraternal twins and other siblings have a slightly higher risk than average children. They are two to four times more likely to develop leukemia.
  
  
• Exposure to high levels of radiation. Children who have been exposed to high levels of radiation, such as x-rays, are at an increased risk of developing ALL. Children who were exposed to radiation within the first few months of development in the womb are five times more likely to develop ALL. Children who have received radiation therapy as treatment for other forms of cancer have an increased risk of developing leukemia.
  
  
• Immune system suppression. Children receiving immunosuppressive drugs (immune system suppressing drugs) are at an increased risk of developing ALL. These drugs are mainly prescribed after an organ transplant.
  
  
• Age. ALL occurs most often in children between the ages of 2 and 3.
  
  
• Race. ALL is slightly more common in white children than African American or Asian American children.
  
  
• Gender. Boys are more likely to develop ALL than girls.
  
  
• Li-Fraumeni syndrome. This condition, resulting from the inheritance of a mutation in the p53 tumor suppressor gene, may increase the risk of developing ALL in some children.
  
  
• Klinefelter syndrome. Boys with this genetic condition have an extra “X” chromosome. Having this disorder makes a boy more likely to develop ALL.
  
  
• Congenital immune deficiency diseases. Being born with an abnormal or deficient immune system increases a child’s risk of developing ALL.
  
  
• Neurofibromatosis. This inherited disorder causes tumors to develop on nerves. Children with this condition are at an increased risk of developing ALL.
  
  
• Ataxia telangiectasia. This rare inherited disorder affects the brain and numerous other tissues and body systems. Children with this condition are at an increased risk of developing ALL.
  
  
• Wiskott-Aldrich. A condition that affects only boys, this inherited disorder is characterized by abnormal antibodies and T-cells, a low platelet count and eczema. Boys with this disorder have a higher risk of developing ALL.
  
  
• Fanconi’s anemia. This inherited disease affects the bone marrow, resulting in decreased production of blood cells. Having this disorder increases a child’s risk of developing ALL.

Although acute lymphocytic leukemia is associated with these risk factors, most children with the disease have no known risk factors.