2.1 Fanconi Anemia

More than 450 mutations in the FANCA gene have been found to cause Fanconi anemia, a disorder characterized by a decrease in bone marrow function, an increased cancer risk, and physical abnormalities. Mutations in the FANCA gene are responsible for 60 to 70 percent of all cases of Fanconi anemia. These mutations change single DNA building blocks (nucleotides) or insert or delete pieces of DNA in the FANCA gene. Some mutations allow production of a FANCA protein that has some residual function; other mutations prevent the production of any FANCA protein. Mutations that prevent all protein production usually lead to a shortage of blood cells at an earlier age and increase the risk of developing cancer of the blood-forming cells (leukemia) as compared to mutations that allow for some FANCA protein production.

Mutations in the FANCA gene lead to a nonfunctional FA core complex, which disrupts the entire FA pathway. As a result, DNA damage is not repaired efficiently and ICLs build up over time. The ICLs stall DNA replication, ultimately resulting in either abnormal cell death due to an inability make new DNA molecules or uncontrolled cell growth due to a lack of DNA repair processes. Cells that divide quickly, such as bone marrow cells and cells of the developing fetus, are particularly affected. The death of these cells results in the decrease in blood cells and the physical abnormalities characteristic of Fanconi anemia. When the buildup of errors in DNA leads to uncontrolled cell growth, affected individuals can develop leukemia or other cancers.