الفهرس 
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Abstract
Acute lymphoblastic leukemia is a malignant disorder of lymphoid progenitor cells. It is the most common pediatric malignancy accounting for about 23 % of all childhood cancers. Polymorphisms in genes encoding components of DNA repair machinery might be relevant to determining susceptibility to ALL.
Genetic polymorphism is the occurrence in a population of two or more genetically determined forms (alleles, sequence variants) in frequencies that the rarest of them could not be maintained by mutation alone, a polymorphic locus is one at which there are at least two alleles each with frequencies greater than 1%. Alleles with frequencies of less than 1% are referred to as rare variants.
5, 10-methylenetetrahydrofolate reductase (MTHFR) is a key enzyme in folate metabolism. Folate provides the one carbon unit required for nucleotides synthesis and for methylation of biological substances. Several polymorphisms in folate-related genes have been described. Two genetic variants in methylenetetrahydrofolate reductase (MTHFR 677 C-T and 1298A-C) have been associated with the risk for adult and childhood acute lymphocytic leukemia.
MTHFR 677 has 3 gene variants; 677C-C has the ”normal” genotype. 677T-T individuals (homozygous) are said to have mild MTHFR deficiency, they have 30 percent in vitro MTHFR enzyme activity compared to those with the wild type (CC). 677C-T individuals (heterozygotes) have been found to have 60 percent wild-type MTHFR enzyme activity.
The aim of this study was to determine the frequency of MTHFR 677C-T gene polymorphism in children with ALL attending the Pediatric Hematology and Oncology clinic at Alexandria University Children’s hospital and its relation to clinical and prognostic criteria of ALL.
The present study was conducted on 40 children with acute lymphoblastic leukemia attending the Hematology / Oncology clinic of the Alexandria Children’s Hospital; they were 27 males and 13 females. Their ages ra