6-巯基嘌呤减量治疗3例急性白血病患儿基因突变分析及临床表现

Analysis of clinical characteristics and genetic mutations of three childhood acute leukemic patients with reduced-dose chemotherapy

目的：分析6-巯基嘌呤（6-MP）减量化疗的急性白血病（AL）患儿维持治疗阶段临床资料及其巯嘌呤甲基转移酶（TPMT）、次黄嘌呤鸟嘌呤磷酸核糖转移酶（HGPRT）基因突变情况，探讨其基因型和临床表型的相关性。方法分别提取3例AL患儿骨髓液及77例对照组儿童外周血总RNA并逆转录成cDNA，PCR特异性扩增TPMT和HGPRT基因蛋白质编码区序列并测序。采用美国国立癌症研究所第3版常规毒性判定标准（NCI CTC 3．0）对维持治疗阶段药物不良反应进行评价和分级，应用国家食品药品监督管理局（SFDA）推荐的药物不良反应关联性评价标准评价6-MP与不良反应发生的相关性。结果1例AL患儿为TPMT＊3C（Try240Cys）纯合突变基因型，减少6-MP剂量至常规剂量1/3～2/3可使骨髓抑制及肝脏毒性等重度不良反应转为轻度。对照组发现2例TPMT＊3 C杂合突变，该位点在人群中的等位基因频率为1.3％。以上两组均未发现HGPRT基因突变。结论 TPMT＊3 C纯合突变患儿可出现与6-MP剂量相关的不耐受现象，中断或减量治疗能够减少维持期间严重药物不良反应的发生。提示TPMT＊3 C基因型的检出可能有利于提高6-MP用药的安全性。

Objective To investigate clinical dates and genetic mutations of hypoxanthine-guanine phosphoribosyl transferase （HGPRT ） and thiopurine methyltransferase （TPMT ） during maintenance therapy in three childhood acute leukemic （AL ） patients with reduced-dose chemotherapy,and to explore the correlation between their genotypes and phenotypes.Methods Total RNA was extracted from bone marrow samples of 3 child patients with AL and 78 peripheral blood of the control group,then reversed them to cDNA.The coding sequence regions of HGPRT and TPMT were amplified with PCR and subjected to direct DNA sequencing.Adverse reactions were evaluated by national cancer institute-common toxicity criteria version3.0 （NCI CTC v3.0）in child patients with during maintenance therapy. The relationships between 6-MP and adverse reactions were classificated by the relevance standard of adverse drug reactions of state food and drug administration （SFDA ）.Results 1 case child patient carried homozygote of TPMT＊3C.Moreover,reducing the dose of 6-MP by 1/3 ~2/3 former dosage should make severe adverse reactions such as myelosuppression and hepatotoxicity more milder.Only two TPMT＊3 C heterozygotes were detected in control group and the allele frequencies was 1 .3%.However, No mutation of HGPRT was found in these three child patients with ALL and controls.Conclusions A child patient who was homozygote of TPMT＊3 C may correlates with the intolerance of dose-related on 6-MP.Discontinued or reduced-dose chemotherapy should be taken into account when serious adverse drug reactions appear during maintenance therapy.Detection of TPMT＊3 C is useful in increasing the safety of drug therapy of 6-MP.