Many types of gene mutations, as well as chromosomal abnormalities, are found in acute leukemia. As we will discuss later, these are in fact a basis of classification, treatment and prognosis.
Typically, it is not just one gene that is mutated, but multiple genetic changes need to occur to cause the leukemia. We describe the genes affected as:
- Oncogenes. These can cause neoplastic conditions through a variety of ways such as changing how procarcinogens are metabolized, disabling the person's ability to repair DNA damage, altering the person's immune system or affecting the regulation of cell growth.
- Protooncogenes. These genes are the upregulators of cell growth and when mutated, can become oncogenes.
- Tumor suppressor genes. These genes are the downregulators of cell growth, and if altered, can result in unchecked proliferation.
The common chromosomal abnormalities seen in acute leukemia that can be visualized on chromosomal analysis include:
- Translocations. A piece of one chromosome can break off and attach to another chromosome. This is one of the most frequently seen chromosomal abnormalities in acute leukemia. The first translocation that was identified, however, was in Chronic Myeloid Leukemia - the famous Philadelphia Chromosome (later this same translocation was found in other leukemias). Translocations can cause altered expression of genes. For instance, they can position a promoter gene to turn on a gene involved in cell cycle and replication.
- Inversions. This occurs when part of the chromosome is turned around, causing altered expression of genes as well.
- Deletions. In a deletion, part of the chromosome breaks off and is lost. If the lost gene(s) are tumor suppressor genes, then replication can continue unchecked.
- Additions. In this abnormality part of a chromosome is gained or there is an additional chromosome. This can cause problems if a number of oncogenes are added.
