Improved pairwise kinship analysis using massively parallel sequencing

In the present study, 67 individuals from two families were analyzed to explore the efficacy of the ForenSeq^™ DNA Signature Prep Kit for pairwise kinship analysis. Six types of pairwise relationships including 81 parent-offspring, 60 full siblings, 48 grandparent-grandchildren, 147 uncle/aunt-nephew/nieces, 97 first cousins and 190 non-relatives were generated from these two families and the corresponding likelihood ratio (LR) was calculated using either sequence-based or length-based STR genotype data (i.e., LR_sequence and LR_length). In addition, 10,000 pairs of different relationships were simulated to estimate the system powers of the STRs and SNPs in this panel. The results showed that 54, 9 and 5 additional alleles were observed based on sequence for 27 autosomal STRs, 24 Y-STRs and 7 X-STRs, respectively, compared to those based on length information and 11 novel alleles were identified. Five mutations were found for 58 STRs in 81 parent-offspring but no mutations were observed for SNPs. For 27 autosomal STR loci, the LRs were increased from 9.20, 7.87, 2.01, 2.07, 0.42 for log₁₀LR_length to 11.52, 10.12, 2.61, 2.60, 0.52 for log₁₀LR_sequence for paternity index (PI), full siblings index (FSI), grandparent-grandchild index (GI), uncle/aunt-nephew/niece index (UNI) and first cousins index (FCI), respectively. PI values for 94 SNPs separated more than those of 27 STRs if two individuals were non parent-offspring relatives. For the simulation study, the effectiveness was 1 for the parent-offspring relationship at the thresholds of t₁ = - 4 and t₂ = 4 and was 0.9998 for full siblings (t₁ = - 2, t₂ = 2). With an error rate of 0.42%, 93.02% of second degree relatives could be identified at the thresholds of t₁ = - 1 and t₂ = 1. However, the effectiveness was only 0.4300 for first cousins with a relatively high error rate of 2.68% (t₁ = - 1, t₂ = 1). In conclusion, STR typing according to the sequence information is more polymorphic, which increases the discrimination power for kinship testing. Compared to these 27 STR markers, 94 SNP markers in this panel have advantages in paternity testing especially when mutated STRs are involved or when a relative is an alleged parent. This panel is powerful enough to resolve paternity and full sibling testing. Most of the second degree relationships could be identified with low error rate while more markers are still needed for first cousins testing.