Acute myeloid leukemia with normal cytogenetics (cytogenetically normal acute myeloid leukemia) - Genes NPM1, FLT3, DNMT3A, CEBPA Idh1 and IDH2.

Acute myeloid leukemia normal cytogenetics (CN-AML) is a form of neoplasia marrow called acute myelogenous leukemia. In normal bone marrow, hematopoietic stem cells give rise to various types of blood cells: leukocytes (protect the body from infection), erythrocytes (carry oxygen) and thrombocytes (involved in blood clotting). In acute myelogenous leukemia, bone marrow produces a large number of abnormal white blood cells and immature cells called mieloblastoides. Instead of becoming normal leukocytes, mieloblastoides cells become neoplastic leukemia cells. The large number of abnormal cells in the bone marrow interferes with the production of leukocytes, erythrocytes and thrombocytes functional.

People with CN-AML have a deficiency of all types of mature blood cells: leucopenia leads to increased susceptibility to infections, anemia causes fatigue and weakness and thrombocytopenia can cause easy bruising and abnormal bleeding. Other symptoms of the disease may include fever and weight loss. The age of onset of the disease ranges from childhood to late adulthood. This disease is considered intermediate risk cancer because the prognosis varies, as some affected individuals respond well to standard treatment, while others may require more powerful treatments. The age of onset of the disease and its prognosis is affected by specific genetic factors.

The normal cytogenetics refers to the fact that this form of acute myeloid leukemia is not associated with large chromosomal abnormalities. About half of people with acute myeloid leukemia have this form of the disease, while the other half have genetic changes that alter large parts of certain chromosomes. These changes can be identified by cytogenetic analysis. CN-AML is associated with smaller genetic changes that can not be identified by cytogenetic analysis.

Acute myeloid leukemia normal cytogenetics is due to mutations in many genes. Most cases are caused by changes in genes NPM1, FLT3, DNMT3A, CEBPA, IDH1 and IDH2. The encoded proteins from these genes have different functions in the cell. Most of them are involved in the regulation of processes such as growth and proliferation, differentiation, or cell survival.

The CEBPA gene, located on the long arm of chromosome 19 (19q13.1), encodes a protein called transcription factor CCAAT / enhancer binding protein alpha. This protein is involved in the differentiation of certain blood cells. It is also believed that acts as a tumor suppressor factor. Mutations in the gene CEBPA are in approximately 18% of individuals with CN-AML. When associated with mutations in the CEBPA gene, this disease can be inherited, in this case as acute myeloid leukemia familiar with mutation CEBPA, or inherited, in which case it is called acute myeloid leukemia sporadic with mutation CEBPA. In form of inherited CN-AML and non - inherited form, two types of mutations may occur in CEBPA gene. A coding type leads to an abnormally short protein that interferes with the tumor suppressor function of normal versions of CCAAT / enhancer binding protein alpha. The other DNA alters to CCAAT / enhancer binding protein alpha binding capacity. Deterioration DNA binding interferes with the ability of the protein to regulate gene expression and affects its tumor suppressor function, leading to uncontrolled coding abnormal leukocytes. Between 50% and 75% of all people with acute myelogenous leukemia with mutations in the gene CEBPA both sporadic and familiar, have two mutated genes in each cell CEBPA. The other has a single genetic mutation CEBPA. The mutation appears only in sporadic cases in the leukemia cells while in familial cases is present throughout the body.

The DNMT3A gene, located on the short arm of chromosome 2 (2p23), encodes an enzyme called DNA (cytosine-5) methyltransferase alpha 3. This enzyme is involved in DNA methylation. DNA methylation is important in many cellular functions including determining whether the instructions in a particular segment of DNA is carried out or is deleted, regulation of reactions involving proteins and lipids, and processing control neurotransmitter. In this sense, the enzyme encoded from DNMT3A gene is particularly important for the establishment of initial locations for methylation during development. In hematopoietic stem cells, methylation patterns established by the enzyme promote differentiation into different types of blood cells. Most mutations in the gene DNMT3A change amino acids in the DNA (cytosine-5) methyltransferase enzyme alpha 3. It is likely that these changes alter DNA methylation, which alters the activity of various genes. For example, it can activate some genes that are normally inactive. It is believed that the activity of the altered gene prevents hematopoietic stem cells carry out normal differentiation, which leads to overproduction of immature leukocytes abnormal.

The FLT3 gene, located on the long arm of chromosome 13 (13q12), encoding a protein tyrosine kinase called 3 fms - like (FLT3), which is part of a family of proteins called receptors tyrosine kinases (RTKs). Tyrosine kinase receptors transmit signals from the cell surface into the cell through a process called signal transduction. FLT3 protein is found in the outer membrane of certain cell types where FLT3 ligand, or FL, can be attached to it. This binding activates the FLT3 protein, which then activates a number of proteins within the cell that are part of multiple signaling pathways. Signaling pathways stimulated by controlling the FLT3 protein results in many important cellular processes such as growth, proliferation and cell survival, particularly hematopoietic progenitor cells. They have identified two types of mutations in the FLT3 gene associated with CN-AML. The most common, occurring in up to 34% of cases of AML-CN is an internal tandem duplication in FLT3 (FLT3-ITD). In this type of mutation, a short sequence of DNA is copied and inserted directly after the original sequence. The duplicate DNA sequence can vary in size, but all FLT3-ITD mutations lead to alterations in the region of the protein that crosses the cell membrane, known as the juxtamembrane domain. The juxtamembrane domain altered allows the FLT3 receptor signaling pathways activated without binding FL, whereby the receptor is constitutively activated. Constant signaling leads to uncontrolled proliferation of abnormal white blood cells, immature, a hallmark of acute myeloid leukemia. The other mutation of the FLT3 gene is found in approximately 14% of people with CN-AML. These mutations are called FLT3 TKD mutations because changing amino acids in a region of the protein known as the tyrosine kinase domain (TKD). The most frequent mutation, the amino acid asparagine replaced by the amino acid tyrosine in position 835 (or Asp835Tyr D835Y). Like the FLT3-ITD mutations, FLT3-TKD mutations lead to a constitutively activated FLT3 receptor and constant signaling, leading to acute myeloid leukemia.

The IDH1 gene, located on the long arm of chromosome 2 (2q33.3) and IDH2 gene, located on the long arm of chromosome 15 (15q26.1), encoding isocitrate dehydrogenase enzyme isocitrate dehydrogenase 1 and 2, respectively. These enzymes convert isocitrate in ketoglutarate 2. This reaction produces a molecule called NADPH necessary for many cellular processes and helps protect cells from reactive oxygen species. Mutations in the gene IDH1 are responsible for about 16% of people with CN-AML, whereas mutations in the IDH2 gene, represent 20% of all cases of AML-CN. Mutations in these genes replaced amino acid isocitrate dehydrogenase and isocitrate dehydrogenase 1 2. These changes alter the usual function of isocitrate dehydrogenase 1 and 2 in the conversion of isocitrate to cetoglutarato2. Instead, the altered enzymes acquire a new function, abnormal: the production of a compound called D-2-hydroxyglutarate. It is likely that an increase in D-2-hydroxyglutarate interfere with the process of determining cell fate. Instead of becoming normal mature cells, immature blood cells with somatic mutations of the gene and IDH2 IDH1 divide without control, leading to CN-AML.

The NPM1 gene, located on the long arm of chromosome 5 (5q35.1), encodes a protein called nucleophosmin found in the nucleolus. It is believed that this protein plays a role in many cellular functions, including the processes involved in protein formation, DNA copying and cell cycle. In the nucleolus, nucleophosmin binds to another protein called ARF, keeping it in the right place and protect it from decomposition. The ARF protein is considered a tumor suppressor. Approximately 64% of people with CN-AML have a mutation in NPM1 gene. These mutations occur in exon 12 of NPM1 gene and lead to encoding a protein with an altered amino acid sequence. Frequently, alterations change the amino acid tryptophan at position 290 the amino acid tryptophan at position 288. These two tryptophans are important for protein localization in the nucleolus. The new sequence also provides a nuclear export signal for the protein to be moved out of the core. Consequently, nucleophosmin protein found in the cytoplasm rather than the nucleolus. Although it is unclear how the abnormal location of nucleophosmin protein leads to acute myeloid leukemia, it is likely to affect the function of the ARF protein. Due to their interaction with altered nucleophosmin, the ARF protein is also found in the cytoplasm in cells with these genetic changes. In addition, nucleophosmin altered protein is unable to protect ARF decomposition. It is believed that a reduction in the tumor suppressor function of ARF protein leads to uncontrolled production of abnormal leukocytes. Other effects of NPM1 gene mutations may also be involved in the development of leukemia.

In general, acute myeloid leukemia with normal cytogenetics (CN-LMA) is not inherited but arises from genetic changes that occur in body cells after conception. Rarely, an inherited mutation in the gene CEBPA leads to acute myeloid leukemia. In these cases, the disease is an autosomal dominant inheritance, which means that a copy of the altered gene in each cell CEBPA is sufficient to express the disease.

Tests performed in IVAMI: in IVAMI perform the detection of mutations associated with acute myeloid leukemia with normal cytogenetics (CN-MAL), by complete PCR amplification of the exons of NPM1, FLT3, DNMT3A, CEBPA Idh1 and IDH2 gene, respectively, and subsequent sequencing.

Samples recommended: EDTA blood collected for separation of blood leukocytes, or impregnated sample card with dried blood (IVAMI may mail the card to deposit the blood sample).