Determination of sibship by PCR‐amplified short tandem repeat analysis in Taiwan

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Abstract
BACKGROUND: Sibship determination for any two persons whose parents have died is one of the most fundamental issues of personal identification, second only to those of a parent‐child relationship. STUDY DESIGN AND METHODS: By automated fluorescence analysis of a PCR‐amplified short tandem repeat (STR) system in conjunction with capillary electrophoresis, a panel of up to 15 polymorphic, autosomal, unlinked STR loci was used to investigate sibship index (SI) values in a cohort of 126 true sibling pairs. These SI values were then compared with those of 126 random pairs. RESULTS: The 15‐loci STR panel provides a cumulative power of exclusion of 0.9999997. Of the 126 random pairs, 124 (98.4%) had cumulative sibship indices (CSIs) of 3.0 (median, 0.0101; range, 0.0000003‐2.5376). In contrast, 107 (85%) of the 126 sibling pairs had a CSI of >100 (median, 5,579.9853; range, 0.0747‐9,406,829,249.8461). However, five pairs (4%) of the sibling group had a CSI of <3.0. True sibship was confirmed for this particular group by additional paternity testing and mitochondrial DNA sequence analysis. Among a total of 1890 observations (15 loci × 126 pairs), two alleles per locus were shared 760 times (40.21%) (mean, 6.03 loci; range, 1‐10) in the sibling group, but only 192 times (10.16%) in the random group (mean, 1.52 loci; range, 1‐5) (p<0.001). No alleles were shared 696 times (36.83%) in the unrelated pairs, as compared to 176 times (9.31%) in the sibling group (p<0.001). A polarized distribution was not noted in the sharing of single alleles in either the random or the sibling group: 1002 observations (53.02%) and 954 observations (50.48%), respectively. CONCLUSION: Highly polymorphic STR analysis can be discriminative in most sibship determinations, and the sharing of two alleles per locus is most informative in indicating sibship. Complementary mitochondrial DNA sequence analysis is mandatory in a few cases to exclude or establish true sibship when CSIs are equivocal and neither parent is available.