The new guidelines for paternity analysis in Germany—how many STR loci are necessary when investigating duo cases?

Abstract

The requirements in the new German guidelines for paternity analysis have not only changed according to the so-called Gendiagnostikgesetz, the new German law regulating human genetic as well as paternity analyses, but also regarding the minimal number of short tandem repeats (STRs) which should be investigated (15 STRs) and the minimal required average exclusion chance (99.999 %). Even in paternity analyses involving only two people (e.g., father and child or mother and child), this exclusion chance is mandatory. A retrospective analysis of 330 father-child cases from our routine investigations showed in 142 cases (43 %) an individual exclusion chance below 99.999 % when using 15 STRs as required, in our routine work provided by the Powerplex® 16 kit which is reported to have an average exclusion chance of 99.988 %. Therefore, these same 330 father-child pairs were additionally analysed using the Powerplex® 21 kit and 120 of these duos were additionally analysed using the Powerplex® ESX17 kit enabling the analysis of 20 or 16 loci respectively. Now, an individual exclusion chance of more than 99.999 % could be achieved in 95.5 % (Powerplex® 21; calculation without the results of D6S1043), 98.8 % (Powerplex® 21; calculation with the results of D6S1043, using allele frequencies established in this study for a German and a West African population) and 98.3 % (Powerplex® ESX17). These data clearly demonstrate that in duo cases, more than the required 15 STR loci have to be investigated to obtain sufficient results.

About the power of biostatistics in sibling analysis—comparison of empirical and simulated data

“…The likelihood of the simulated/observed genotype data of the pairs was then calculated under three different hypotheses about their relationship (full sibs, half sibs, and unrelated). Likelihood ratios and W-values were calculated for pairs of the three hypotheses using frequency data from our own study of unrelated Germans [13].…”

“…Table 7 Results for calculating full sibship versus unrelated from 112 pairs of unrelated people in comparison to simulated data. Calculations were done using German population frequencies [13] …”

“…Recently, multiplex PCRs were developed comprising even more loci, such as the GlobalFiler® with 24 loci (Applied Biosystems) or the Powerplex® 21 providing 20 STR loci (Promega). The latter was already tested in own studies and showed great potential for a forensic approach [13].…”

“…Calculations were done using German population data[13] after amplification of 15 STRs or 20STRs. Data for testing these same twins in a half sibship versus unrelated hypothesis is given in brackets…”

Development of a polymorphic short tandem repeat locus multiplex system for efficient human identification

“…In this sense, Poetsch et al (2013) concluded that the number of hypervariable loci available for a genetic linkage analysis is directly associated with the percentage of certainty established during the assessment of the analysis (Børsting et al, 2008;Rodovalho et al, 2015;Zhang et al, 2015). Therefore, it is critical that STR panels provide sufficient security, permitting an accurate and unfailing conclusion regarding the genetic linkage analysis.…”