Single Nucleotide Polymorphisms Of MTHFR,CASP8 Genes And Acute Lymphocytic Leukemia

BACKGROUND &OBJECTIVE:High-dose methotrexate (HDMTX), which interrupts folate metabolism, is used in the treatment of acute lymphoblastic leukemia (ALL), but exerts different toxic effects in ALL patients received the same dose MTX.Methylene tetrahydrofolate reductase (MTHFR) is a rate-limiting enzyme in folate metabolism and has two common variants with reduced activity due to polymorphisms at nucleotides 677 and 1298. Both are thought to affect nucleotide synthesis,DNA repair and methylation.The enhanced toxicity may be due to cooperative effects between MTX and MTHFR variants. We studied the association between MTHFR gene polymorphisms and toxicity of HDMTX in ALL patients.Immune surveillance disorder causes ALL. CASP8 plays an important role in immune-cell life and death , therefore genetic variant in CASP8 gene may influence immune surveillance of malignancies.A 6-nucleotide deletion (?652 6Ndel) variant in the CASP8 promoter destroys an Sp1 binding site, decreases CASP8 transcription, reduces T lymphocyte apoptosis and enhances antitumor activity. Based on genetic variant influencing immune status confers cancer susceptibility,we analysised the relationship between -652 ins/del polymorphism in CASP8 gene and the risk of T-ALL.METHODS:Forty-four patients with a diagnosis of ALL were treated with HDMTX and toxicity response was observed according to World Health Organization grades in 1981.Genomic deoxyribonucleic acid(DNA) was extracted from their peripheral blood and genotype analysis of MTHFR gene was done by polymerase chain reaction/restriction fragment length polymorphism (PCR-RFLP) techniques. We analyzed the date of age,gender,white blood count(WBC),frequency of allele and genotype by Chi square .The adjusted odds ratios (ORs) and 95% confidence interval (CIs) were calculated using unconditional logistic model to investigate the relationship between the risk genotypes and HDMTX toxicity in ALL patients.The subtypes of ALL patients (n=118),which were diagnosised by bone morphocytology check, determined by immunophenotyping were as T,B-cell.The association analysis between the T-ALL cases and B-ALL controls was conducted.The same empirical and statistical methods as mentioned above were used to analysis CASP8 -652 6Nins/del polymorphism and suscentibility to T-ALL.RESULTS:1. Of the 44 patients,the frienquencies of MTHFR 677CC, CT and TT genotype were 34.9%, 30.2% and 34.9%, while the frienquencies of MTHFR 1298AA, AC and CC genotype were 71.4%, 26.2% and 2.4% respectively.2. The rate of toxicity response in the patients with MTHFR C677T was CC genotype 40%,CT genotype 53.9% and TT genotype 86.7%,while the rate of no toxicity was CC genotype 60%,CT genotype 46.1% and TT genotype 13.3%. There was significantly difference of toxicity response rate among CC,CT and TT genotypes(p=0.028),the patients with CT+TT genotypes increased risk of HDMTX toxicity compared with CC genotype(OR=3.75,95%CI:1-14,p=0.04).3. The rate of toxicity response in the patiences with MTHFR A1298C was AA genotype 73.3% and AC genotype 27.3%,while the rate of no side effect was AA genotype 26.7%,AC genotype 72.3% and CC genotype 100%, There was significantly difference of toxicity response rate among AA, AC and CC genotypes(p=0.006),the patients with AC+CC genotypes decreased risk of HDMTX toxicity compared with AA genotype. The patients with AC and CC genotypes had a 0.12-fold(OR=0.12,95%CI:0.026～0.564,p=0.007).4. The incidence rate of vomiting/nausea/diarrheain C677T TT genotype was significantly higer than other C677T genotype.The incidence rate of myeolosuppression, vomiting/nausea/diarrhea,skmatitis and the damage of liver in A1298C AA genotype was significantly higher than A1298C AC+CC genotypes. 5 The response rate of toxicity among patients with MTHFR C677T TT genotype and A1298C AA genotype was significantly higer than MTHFR C677T CC genotype and A1298C AC+CC genotype(p=0.018), the patients with TT and AA genotypes had a 16.5-fold(OR=16.5,95%CI:1.07～74.86).6. The frienquencies of CASP8-652 6Nins/ins,ins/del and del/del genotypes were 78.9%,15.8% and 5.3% in T-ALL, while the frienquencies were 43.8%,45.0% and 11.2% in B-ALL. The distributions of the CASP8 -652 6Nins/del genotypes were significantly different between the T-ALL cases and B-ALL controls(p=0.002).7. The CASP8 -652 6Nins/del and del/del genotypes were associated with significantly decreased risk of T-ALL , compared with the CASP8 -652 ins/ins genotype, the patients with ins/del and del/del genotypes had a 0.21-fold(OR=0.21, 95%CI:0.085～0.508,p=0.0003).CONCLUSION:1. MTHFR gene polymorphisms are associated with the toxicity of HDMTX in ALL.2. Genotype of MTHFR 677TT and/or 1298AA indicate most severe toxical response;3. A six-nucleotide insertion-deletion polymorphism in the CASP8 promoter is associated with susceptibility to T-ALL.4. CASP8-652 6Ndel genetic variant may decrease risk of T-ALL.