Objective To investigate the criterion for source identification of gastrointestinal tumor based on the number of identical allele(lAn) and the number of matched STR locus with 2 identical alleles(Aa) in Identifiler system. Methods One hundred and five pairs of gastrointestinal tumor samples and homologous normal samples (TN group) were genotyped with Identifiler system. The numbers of STR locus with genotypic alteration (STRGA) in each tumor were determined by comparing the genotype of the matched STR loci in each pair of samples. According to the limited distribution of IAn and A2, 16 different values of IAn was substituted into the published discriminant functions to obtain the cut-off values of IAn and A2 for source identification of tumor sample. Indices including sensitivity (SEN), specificity (SPE), accuracy (AC),positive predictive value(PPV) and negative predictive value(NPV) for distinguishing tumor from an unrelated individual or a full sibling of the patient were calculated. Concordance of the identification results based on the determined criteria and the definite facts were statistically tested with Kappa index. Results The total frequency of STRCA was 5.46％. There were 31.43％ of the 105 tumor samples carried at least one STR locus with STRgA mutation. According to the Fisher discrimination rules, criteria I (IAn≥23 and A2≥8) and criteria Ⅱ (IAn≥26 and A2≥ 11) meet the requirements of distinguishing tumor sample from an unrelated individual or a full sibling of the patient with tumor, respectively. SEN=0.971 0, PPV=1.0000,PPV=0.891 9 and Kappa=0.923 5, when the criteria were used to determine the specified relatives. Conclusion Criteria I and criteria II were powerful for distinguishing tumor sample from an unrelated individual or a full sibling of the patient with tumor, respectively, when the Identifiler system was adopted for source identification of gastrointestinal tumor sample.%目的 探讨采用Identifiler系统进行消化系统肿瘤组织身源判定时共有等位基因数(IAn)和全相同基因座数(A2)的标准.方法 在对l05对消化系统肿瘤组织-身源正常组织对进行Identifiler系统分型的基础上,依据IAn和A2的有限分布原则,将IAn的16种取值代入已建立的相应判别函数,通过Fisher判别准则确定采用IAn和A2能够判定消化系统肿瘤组织身源的最小值.依据这一标准,对105对消化系统肿瘤组织-身源正常组织对进行判定,计算该标准甄别肿瘤身源者与无关个体、肿瘤身源者与其全同胞的敏感度、特异性、准确度、阳性预测值和阴性预测值,通过Kappa检验比较基于IAn和A2的判定标准与金标准的一致性.结果 消化系统肿瘤组织中STR基因座基因型变更(STRGA)的检出率为5.46%,至少出现1个STRGA基因座者占31.43%.依据Fisher判别准则,当满足标准Ⅰ(IAn≥23且A2≥8)时可甄别肿瘤身源者与无关个体,当满足标准Ⅱ(IAn≥26且A2≥11)时可甄别肿瘤身源者与其全同胞.上述标准甄别相应关系时准确度均为0.9710,阳性预测值均为1.0000,阴性预测值均为0.8919.一致性检验显示上述标准对肿瘤组织身源的判定结果与金标准判定结果的Kappa值均为0.9235.结论 采用Identifiler系统进行消化系统肿瘤组织身源判定时,标准Ⅰ和标准Ⅱ可分别用以甄别肿瘤身源者与无关个体和肿瘤身源者及其全同胞.
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