RMplex reveals population differences in RM Y-STR mutation rates and provides improved father-son differentiation in Japanese.

Rapidly mutating Y chromosomal short tandem repeat markers (RM Y-STRs) -characterized by at least one mutation per 100 generations- are suitable for differentiating both related and unrelated males. The recently introduced multiplex method RMplex allows for the efficient analysis of 30 Y-STRs with increased mutation rates, including all 26 currently known RM Y-STRs. While currently available RM Y-STR mutation rates were established mostly from European individuals, here we applied RMplex to DNA samples of 178 genetically confirmed father-son pairs from East Asia. For several Y-STRs, we found significantly higher mutation rates in Japanese compared to previous estimates. The consequent father-son differentiation rate based on RMplex was significantly higher (52%) in Japanese than previously reported for Europeans (42%), and much higher than with Yfiler Plus in both sample sets (14% and 13%, respectively). Further analysis suggests that the higher mutation and relative differentiation rates in Japanese can in part be explained by on average longer Y-STR alleles relative to Europeans. Moreover, we show that the most striking difference, which was found in DYS712, could be linked to a Y-SNP haplogroup (O1b2-P49) that is common in Japanese and rare in other populations. We encourage the forensic Y-STR community to generate more RMplex data from more population samples of sufficiently large sample size in combination with Y-SNP data to further investigate population effects on mutation and relative differentiation rates. Until more RMplex data from more populations become available, caution shall be placed when applying RM Y-STR mutation rate estimates established in one population, such as Europeans, to forensic casework involving male suspects of paternal origin from other populations, such as non-Europeans.

Improving the differentiation of closely related males by RMplex analysis of 30 Y-STRs with high mutation rates.

The discovery of rapidly mutating (RM) Y-STRs started to move the field of forensic Y-STR analysis from male lineage identification towards male individual identification. Previously, the forensic value of RM Y-STRs for differentiating male relatives was limited due to the modest number of 13 identified RM Y-STRs. Recently, new RM Y-STRs were discovered, with strong expectations for significantly improving male relative differentiation; however, empirical evidence is missing yet. More recently, the genotyping method RMplex for efficiently analyzing 30 Y-STRs with high mutation rates, including all 26 currently known RM Y-STRs, was introduced. Here, we applied RMplex as well as the current state-of-the-art commercial Y-STR kit: Yfiler™ Plus PCR Amplification kit, to several hundreds of DNA-confirmed father-son pairs. Newly established estimates confirmed the high mutation rates of novel and previous RM Y-STRs. By combining current with previous data, we provide updated consensus estimates of mutation rates for all 49 Y-STRs targeted with both methods. Based on RMplex, 42% of 499 father-son pairs were differentiated, while 14% of 530 pairs based on Yfiler™ Plus, and 48% of 499 pairs based on both methods combined. Regarding brothers, RMplex also clearly outperformed Yfiler™ Plus, with differentiation rates of 62% and 33%, respectively. By combining both methods 72.9% of the brothers showed at least one mutation. For unrelated males, both methods achieved a discrimination capacity of 99.8% and a haplotype diversity of 0.999991, since all males had different haplotypes, except for two, perhaps indicating a hidden paternal relationship. Overall, this study underlines the value of RM Y-STRs in general and RMplex in particular for differentiating male relatives highly relevant in forensic genetics. It provides the first empirical evidence on the high value of RMplex for differentiating close male relatives, which for father-son pairs was almost 60% higher than with the initial set of 13 RM Y-STRs and three times higher than with Yfiler™ Plus. Based on our results from closely related males, we expect RMplex to also improve the differentiation of more distantly related males significantly, which needs empirical demonstration in future studies. We encourage the forensic community to apply RMplex in all forensic cases where a match with a commercial Y-STR kit was obtained between the male suspect and the evidence material, or to solely use RMplex in such cases, aiming to find out if the male suspect or any of his male paternal relatives left the evidence material at the crime scene.

Identification and characterization of novel rapidly mutating Y-chromosomal short tandem repeat markers.

Short tandem repeat polymorphisms on the male-specific part of the human Y-chromosome (Y-STRs) are valuable tools in many areas of human genetics. Although their paternal inheritance and moderate mutation rate (~10-3 mutations per marker per meiosis) allow detecting paternal relationships, they typically fail to separate male relatives. Previously, we identified 13 Y-STR markers with untypically high mutation rates (>10-2 ), termed rapidly mutating (RM) Y-STRs, and showed that they improved male relative differentiation over standard Y-STRs. By applying a newly developed in silico search approach to the Y-chromosome reference sequence, we identified 27 novel RM Y-STR candidates. Genotyping them in 1,616 DNA-confirmed father-son pairs for mutation rate estimation empirically highlighted 12 novel RM Y-STRs. Their capacity to differentiate males related by 1, 2, and 3 meioses was 27%, 47%, and 61%, respectively, while for all 25 currently known RM Y-STRs, it was 44%, 69%, and 83%. Of the 647 Y-STR mutations observed in total, almost all were single repeat changes, repeat gains, and losses were well balanced; allele length and fathers' age were positively correlated with mutation rate. We expect these new RM Y-STRs, together with the previously known ones, to significantly improving male relative differentiation in future human genetic applications.

A comprehensive mutation study in wide deep-rooted R1b Serbian pedigree: mutation rates and male relative differentiation capacity of 36 Y-STR markers.

Haplotyping of Y-chromosomal short tandem repeats (Y-STRs) reflects the paternal lineage, although, the father-son pair profiles may differ due to the germline mutations. In order to discriminate between closely related males in criminal cases, as well as for the correct application of Y-STRs in the paternity/kinship analysis and determination of the most recent common ancestor in the familial searching or genealogy research, the assessment of mutation rates of routinely used Y-STRs is of a great importance. We genotyped 120 males belonging to one wide deep-rooted pedigree separated by 1-20 meiosis. The haplotypes of analyzed males distributed over 12 different families (according to their surnames), with 113 originating from one ancestor, and the remaining 7 from the second, closely related to the previous one, belong to the R1b haplogroup. The analysis was performed using Powerplex® Y23 kit, Yfiler™ plus kit and 13 rapidly mutating (RM13) Y-STRs. In 20,855 allele transmissions, 175 mutations (61% repeat losses and 39% gains) and one gene conversion event were found at 25 out of 36 markers. The medians of locus-specific mutation rates estimated using the Bayesian approach ranged from 1.42 × 10-3 (95% credible interval (CI): 0.05 × 10-3 - 7.56 × 10-3) for loci with no observed mutations to 130.91 × 10-3 (95% CI: 102.91 × 10-3 - 162.78 × 10-3) for DYF399S1, with a median rate across all 36 markers of 10.06 × 10-3 (95% CI: 8.65 × 10-3 - 11.61 × 10-3). In 6349 male relative pairs, the 36 Y-STR set distinguished 98.4% relative pairs by at least one mutation, compared to 95.9%, 65.5% and 57.4% for RM13, Yfiler™ plus, and Powerplex® Y23 set, respectively. The extra-pair paternity rate was estimated at 11.9 × 10-3 (95% CI: 4.4 × 10-3 - 25.8 × 10-3) fitting within the range reported for some European populations. A significant positive correlation was observed between fathers' ages at the time of the Y chromosome transmission and mutability rates (R2 = 0.9495, p = 0.0256), with more significant results when analyzing RM markers (R2 = 0.9827, p = 0.0087).

Improving empirical evidence on differentiating closely related men with RM Y-STRs: A comprehensive pedigree study from Pakistan.

Y-chromosomal short tandem repeat (Y-STR) markers are commonly used in forensic genetics. Male-specific haplotypes provided by commercial Y-STR kits allow discriminating between many - but not all - unrelated men, while they mostly fail to separate related ones. Aiming to improve male relative and paternal lineage differentiation, a set of 13 rapidly-mutating (RM) Y-STRs was previously identified and introduced to forensic Y-chromosome analysis. Recently, their value was highlighted by separating 99% of over 12,200 unrelated men from 111 global populations, as well as 29% of over 2500 male relative pairs, the vast majority were father-sons. Here, we provide improved empirical evidence on differentiating closely related men with RM Y-STRs, most notably beyond father-sons, where previous data were limited. After careful quality control including genetic relationship testing, we used 572 Pakistani men belonging to 99 2-4 generation pedigrees covering 1568 pairs of men related by 1-6 meioses. Of those, 45% were differentiated by one or more of the 13 RM Y-STR markers. In contrast, only 14.7% of a subset of 1484 pairs from 94 pedigrees were separated by the commercial AmpFlSTR Y-filer kit. Combining previously published and new data, an overall differentiation rate of 35.3% was revealed for the RM Y-STR set based on 4096 pairs of men related by 1-20 meioses, compared to 9.6% with Y-filer based on 3645 pairs. Using father-son pair data from the present and previous studies, we provide updated RM Y-STR mutation rates. Locus-specific mutation rates ranged from 2.0×10-3 (7.0×10-4-4.3×10-3) to 6.9×10-2 (6.1×10-2-7.9×10-2) based on 2741-3143 meioses, with an average rate across all 13 RM Y-STR markers of 1.8×10-2 (1.7×10-2-1.9×10-2) based on 800 mutations from 44,922 meioses. The high haplotype diversity (h=0.9996) we observed among the unrelated men (N=105) underlines the value of this RM Y-STR set to differentiate paternal lineages even from endogamous populations such as from Pakistan.