Targeted High Throughput Sequencing in the Diagnosis of Pediatric Acute Leukemia
Targeted High Throughput Sequencing in the Diagnosis of Pediatric Acute Leukemia
Acute leukemias are a heterogeneous group of hematologic malignancies. They result from clonal expansion of immature cells whose number is greater than 20% in bone marrow. Childhood acute leukemias are the most common pediatric malignancies. In Europe and the United states, they represent about 35% of childhood cancers. 80% of them are acute lymphoblastic leukemia (ALL) and 15-20% of acute myeloid leukemia (AML). Current treatments allow a cure in about 80% of ALL, while this level is only 50% in AML.Acute leukemia diagnosis is based on the multidisciplinary exploration of leukemia cells by different techniques:
Cytogenetic studies are performed at time of acute leukemia diagnosis. Indeed, the WHO 2008 classification of acute leukemia is based largely on the presence of recurrent cytogenetic and molecular abnormalities. The most frequent chromosomal aberrations have been associated with specific clinical and biological characteristics and are now used as diagnosis and prognostic markers. These chromosomal abnormalities affect genes involving in the leukemogenesis process. These rearrangements are of several types:
Fusion genes causing :
Deregulation of genes expression: chromosomal rearrangements can sometimes induce deregulation of adjacent genes to the breakpoint. For example, inv(3)(q21q26) or t(3;3)(q21;q26) induce over expression of transcriptional factor EVI-1.
Loss of function due to deletion of variable size in genomic regions containing genes with a role in the differentiation, apoptosis, or cell proliferation (eg IKZF1, PAX5…)
In addition to the karyotype, which allows to have a global view of the genome; FISH, a targeted technique, is used to highlight invisible abnormalities on karyotype (cryptic abnormalities) or the time of karyotype failure. However, conventional and molecular cytogenetic techniques do not highlight any abnormalities (eg different partners involved in the formation of fusion genes in particular for MLL gene rearrangement, mutations) hence our interest in next generation sequencing.Indeed, the high throughput targeted sequencing messenger RNAs (RNA-seq) has the avantage of allow identification of different types of mutations in a single test, with exception of epigenetic mutations. The importance of RNAs sequencing rather than DNA genomic is the one hand, a very significant decrease in the volume of sequences to analyze because transcribed mRNA genes represent about 5% of the genome size and secondly, a better identification of chimeric genes. The RNA-seq has used as a research tool in hematologic malignancies. The purpose of this project is to use innovative technology to develop a new diagnostic and prognostic new tool in hematological malignancies. 50 acute leukemias will be tested and results will be analyzed according to three criteria:
Inclusion Criteria:
Exclusion Criteria: