Full siblings impersonating parent/child prove most difficult to discredit with DNA profiling alone

Performance of a 74-Microhaplotype Assay in Kinship Analyses

Microhaplotypes (MHs) consisting of multiple SNPs and indels on short stretches of DNA are new and interesting loci for forensic genetic investigations. In this study, we analysed 74 previously defined MHs in two of the populations that our laboratory provides with forensic genetic services, Danes and Greenlanders. In addition to the 229 SNPs that originally made up the 74 MHs, 66 SNPs and 3 indels were identified in the two populations, and 45 of these variants were included in new definitions of the MHs, whereas 24 SNPs were considered rare and of little value for case work. The average effective number of alleles (Ae) was 3.2, 3.0, and 2.6 in Danes, West Greenlanders, and East Greenlanders, respectively. High levels of linkage disequilibrium were observed in East Greenlanders, which reflects the characteristics of this population that has a small size, and signs of admixture and substructure. Pairwise kinship simulations of full siblings, half-siblings, first cousins, and unrelated individuals were performed using allele frequencies from MHs, STRs and SNPs from Danish and Greenlandic populations. The MH panel outperformed the currently used STR and SNP marker sets and was able to differentiate siblings from unrelated individuals with a 0% false positive rate and a 1.1% false negative rate using an LR threshold of 10,000 in the Danish population. However, the panel was not able to differentiate half-siblings or first cousins from unrelated individuals. The results generated in this study will be used to implement MHs as investigative markers for relationship testing in our laboratory.

An incest case with three biological brothers as alleged fathers: Even 22 autosomal STR loci analysis would not suffice without the mother

Here, we report an incest paternity case involving three biological brothers as alleged fathers (AFs), their biological sister and her child that was investigated using the Investigator ESSplex Plus, AmpFLSTR Identifiler Plus/Investigator IDplex Plus and PowerPlex 16 kits. Initial duo paternity investigations using 15-loci autosomal short tandem repeat (STR) analyses failed to exclude any of the AFs. Despite the fact that one of the brothers, AF1, had a mismatch with the child at a single locus (D2S1338), the possibility of a single-step mutation could not be ruled out. When the number of autosomal STR loci analysed was increased to 22 without the inclusion of the mother, AF2 and AF3 still could not be excluded, since both of them again had no mismatches with the child. A breakthrough was possible only upon inclusion of the mother so that trio paternity investigations were carried out. This time AF1 and AF2 could be excluded at two loci (D2S1338 and D1S1656) and six loci (vWa, D1S1656, D12S391, FGA, PENTA E and PENTA D), respectively, and AF3 was then the only brother who could not be excluded from paternity. Subsequent statistical analyses suggested that AF3 could be the biological father of the child with a combined paternity index >100 billion and a probability of paternity >99.99999999%. These findings consolidate the fact that complex paternity cases such as those involving incest could benefit more from the inclusion of the mother than simply increasing the number of STR loci analysed.

The risk of false inclusion of a relative in parentage testing - an in silico population study

Aim

To investigate the potential of false inclusion of a close genetic relative in paternity testing by using computer generated families.

Methods

10 000 computer-simulated families over three generations were generated based on genotypes using 15 short tandem repeat loci. These data were used in assessing the probability of inclusion or exclusion of paternity when the father is actually a sibling, grandparent, uncle, half sibling, cousin, or a random male. Further, we considered a duo case where the mother’s DNA type was not available and a trio case including the mother’s profile.

Results

The data showed that the duo scenario had the highest and lowest false inclusion rates when considering a sibling (19.03 ± 0.77%) and a cousin (0.51 ± 0.14%) as the father, respectively; and the rate when considering a random male was much lower (0.04 ± 0.04%). The situation altered slightly with a trio case where the highest rate (0.56 ± 0.15%) occurred when a paternal uncle was considered as the father, and the lowest rate (0.03 ± 0.03%) occurred when a cousin was considered as the father. We also report on the distribution of the numbers for non-conformity (non-matching loci) where the father is a close genetic relative.

Conclusions

The results highlight the risk of false inclusion in parentage testing. These data provide a valuable reference when incorporating either a mutation in the father’s DNA type or if a close relative is included as being the father; particularly when there are varying numbers of non-matching loci.

Pretense of parentage by siblings in immigration: Polesky's paradox reconsidered

BACKGROUND

Older and younger siblings occasionally attempt to impersonate parent and child to expedite immigration under US family-based visa policies. The rate with which full siblings escape detection by current relationship tests is unknown.

STUDY DESIGN AND METHODS

Retrospective study of full-sibling immigrant pairs was undertaken to determine the proportion that show insufficient genetic evidence to exclude parentage. Sibship and parentage indices (SI and PI) were compared/case in unexcluded sibling cases and true parent-child cases. Alleles shared per short-tandem-repeat locus were compared in sibling and parent-child pairs. The proportion of successful parentage fraud by siblings was estimated from the parentage exclusion rate among immigrants and the proportion of sibships without genetic inconsistencies (GIs).

RESULTS

When 11 to 25 independent loci were tested per two-sibling case to verify or refute parentage, tests failed to demonstrate any GI in 9% and PI was greater than SI in seven of 10 of these cases. Another 29% of full-sibling pairs demonstrated insufficient evidence (fewer than two GIs) to exclude parentage. Thus, 0.4% of sibling pairs could falsely claim a parent-child relationship and show no GIs. Another 1.4% could make that false claim and not present sufficient evidence to be excluded.

CONCLUSION

At present, with no evidence of parentage exclusion in a full-sibling pair, the relative magnitudes of PI and SI are misleading relationship indicators because too few loci are examined and rates of sharing one and two alleles/locus vary greatly in parentage and sibling pairs. Only evidence of exclusion ascertains false parentage claims by siblings. Nevertheless, the expected rate of successful fraud is quite low.

Paternity exclusion power: comparative behaviour of autosomal and X-chromosomal markers in standard and deficient cases with inbreeding

In paternity testing the informativeness of genetic markers is traditionally measured through the probability of finding, in randomly chosen individuals, inconsistencies with parent to child Mendelian rules of transmission. This statistic, called power of exclusion (PE), paternal exclusion chance or probability, can be defined for duos (mother not typed) or trios (random false fathers are matched against mother/child pairs) and performed both for autosomal and X-chromosomal markers (restricted to paternity testing involving daughters). PE is an a priori statistic, in the sense of not depending on the individual's genetic data of a case, being dependent however on the estimates of genetic markers allele (or haplotype) frequencies. We have studied the behaviour of this statistic in situations where the randomness assumption is not met, because either (a) the alleged - and false - father is related to the true one, or (b) there is a non-negligible level of background relatedness in the population. For the first case, we derived general (autosomal and X-chromosomal) PE formulas for duos and trios for any genealogy linking alleged father and child, highlighting that the PE of each marker only depends on a single kinship parameter associated with their pedigree. In this case we also estimate a lower bound for the number of extra markers needed to be analysed to achieve the same global power as for unrelated individuals. In the second situation, we demonstrate that for realistic values of the coancestry coefficient the decrease in PE due to population inbreeding is very moderate even when duos are analysed. In this work, beyond the aforementioned issues, we also discuss the suitability of assuming the pedigree father-daughter for calculating the X-PE, since X-markers are not the tool of choice in laboratorial routine when the alleged father is available for testing. Indeed, X-markers are particularly useful in situations where the alleged father is not available for testing but experts are able to type the mother or a daughter of his. Such increase of power is due to the paternal genealogies: half- and full-sisters, and grandmother-granddaughter, having a non-null X-PE even when only duos are analysed in contrast to what happens for autosomes. Algebraic expressions for these cases are also presented.

DNA profiling: Social, legal, or biological parentage

DNA profiling in forensic casework is based on comparison of the results of biological evidence with direct reference samples of the individual concerned or with indirect references of his close blood relatives. The selection of reference samples for analysis is crucial to the success of a case; it not only depends on the authenticity of the reference samples, but also on the authenticity of the biological relation of the donors with the person in question. There are situations when the social or legal relationship is not the biological one and there is a need to educate investigating officers, forensic analysts, and the judiciary about the associated problems.

Use of X-linked short tandem repeat loci in routine parentage casework

BACKGROUND

Dealing with genetic inconsistencies in parentage testing, especially in motherless cases, remains a continual difficulty.

STUDY DESIGN AND METHODS

Four difficult cases, comprising two trios and two duos, were selected from routine parentage testing casework. In these, relatively low combined paternity indices were observed as a result of few discrepant loci that were treated as being due to paternal mutations. An additional eight short tandem repeat (STR) loci along the X chromosome were studied in the alleged father and female child to try and help resolve these cases.

RESULTS

In all four cases, the X chromosome haplotypes in the alleged father were different from those in the child, showing decisively that the alleged father could be excluded from being the biologic father of the child.

CONCLUSION

In recent times the study of X chromosome haplotypes has been shown to be useful in parentage testing where the alleged father is absent and where only his close relatives are available for testing. This work demonstrates that such studies can also prove valuable in the testing of standard trios and duos in cases where there only a few genetic inconsistencies amongst the loci tested, making it difficult to distinguish between paternal mutations and a close relative of the alleged father being the biologic father.

Y-chromosome short tandem repeats analysis to complement paternal lineage study: a single institutional experience in Taiwan

BACKGROUND

Highly polymorphic autosomal short-tandem-repeat (STR) analysis can be useful in most kinship testing. Y-chromosome-specific STRs, in contrast, have been increasingly applied for the verification of equivocal paternal genetic transmissions.

STUDY DESIGN AND METHODS

A total of 338 unrelated males were first typed for the 9-loci Y-STR European minimal haplotype (minHt). Samples with haplotypes that were found at least two times were subject to further study by a commercially available 17-Y-STR multiplex set (AmpFlSTR Yfiler). A separate clinical study for 113 various kinship identifications of male genetic transmission were then conducted by a panel consisting of 18 autosomal STRs and complemented by both Y-STR multiplex sets and their respective results compared.

RESULTS

For the 338 individuals, a total of 270 haplotypes were identified after the minHt study, of which 234 were unique. Among the rest of the 104 samples, AmpFlSTR Yfiler identified 82 other unique haplotypes. Altogether, 324 different haplotypes were observed; 316 (97.5%) were unique whereas 8 were shared by two to seven times. The haplotype diversities for the minHt and the AmpFlSTR Yfiler were 99.75 and 99.96 percent, respectively, whereas the powers of discrimination (PDs) were 79.88 and 95.86 percent, respectively. Despite a lower PD for minHt, there was no discrepancy on the clinical setting for personal identification between the two Y-STR sets in an allegedly true male lineage transmission involving 66 cases with 24 father-son, 19 siblings, 9 uncle-nephew, 8 grandfather-grandson, 3 cousins, and 3 half-siblings. For 47 other cases with a false allegation of paternity, exclusion was made for all without ambiguity by either Y-STR panel.

CONCLUSION

The 9-loci minHt Y-STR set is adequate to complement conventional autosomal STRs for kinship studies where Y-lineage transmission is concerned.

Possible pitfalls in motherless paternity analysis with related putative fathers

Nowadays, more and more paternity cases are carried out investigating only child and putative father, mostly for economical or private reasons. Usually, reliable results can be obtained and the putative father can be included or ruled out with a high certainty. Considerable problems might arise when a relative of the biological father is investigated as being the putative father. In this study, we investigated 164 persons from 27 families creating artificial deficiency cases using the AmpFlSTRIdentifiler kit, which amplifies 15 STRs simultaneously. We analyzed 93 child/biological father pairs and the corresponding uncles, respectively the brothers of the biological fathers. The average paternity probability for the biological father was 99.9699% (paternity index (PI): 3321.26); only in three cases the results were under 99.9%. In five out of 125 child/uncle pairs no STR mismatches were found and paternity probabilities between 99.9726% (PI 3652) and 99.9970% (PI 33,545) were calculated. The average number of excluding loci was 3.4, but in 31.2% of the cases only zero, one or two mismatches were found. When both putative fathers were genetically typed, the biological father usually had a statistically higher paternity probability. Nevertheless, the differences between probabilities for father and uncle were only small. These results show that a reliable investigation of deficiency cases (i.e. child and putative father) seems to be more difficult than generally assumed. Especially in cases with an unknown familiar background and/or when investigating foreigners for immigration purposes, the laboratory expert should include the mother, increase the number of investigated loci or include a second method such as RFLP-analysis, some serological systems or typing of X-chromosome specific STRs to further ascertain the results.