CPI Distribution and Cutoff Values for Duo Kinship Testing

Chang-En Pu；Adrian Linacre

forensic science ； short tandem repeat STRs ； paternity ； false inclusion duo ； sensitivity ； specificity

The Chinese Journal of Physiology

50卷5期（2007 / 10 / 31）

232 - 239

英文

DNA-based tests commonly use 13 STR (short tandem repeat) loci in human identification and paternity testing-the Combined DNA Index System or CODIS. Its average degree of accuracy of paternity identification is greater than 0.9999 under the circumstance of a mother, a child and a putative father. However, the possibility of false inclusions increases under circumstances such as [1] only two members of a family group are available-a duo case during determination of paternity or [2] identification of human remains while only one living relative is present. In Taiwan, the National Unidentified Human Remains Database uses the CODIS 13 STR for the identification of family members. Two or more reference samples in the DNA database have been found to share one allele at all loci tested. Then the Combined Paternity Index (CPI) is used to determine and provide an estimate of kinship in such cases. Combining 499,500 sets of DNA data for the 13 STR CODIS loci, totally 431 (0.086%) cases are false inclusions where all 13 loci shared at least one allele. Simulated partial DNA profiles (not all 13 loci yielded results) were created to mimic the mutation and degradation process. All 431 real duo cases were analyzed to evaluate sensitivity and specificity. This report provided four kinship-matching situations with CPI cutoff values when the number of allele-sharing loci exceeded 11. CPI values greater or lesser than the suggested cutoff point will provide a greater degree of confidence in determining whether two samples are derived from first-degree relatives.

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