Evaluating genome-wide and targeted forensic sequencing approaches to kinship determination

Kinship determination is a valuable tool in forensic genetics, with applications including familial searching, disaster victim identification, and investigative genetic genealogy. Conventional typing of small numbers of autosomal short tandem repeats (STRs) confidently identifies only first-degree relatives. Massively parallel sequencing (MPS) can access more STRs and resolve alleles identical by length but differing in sequence (isoalleles), which may increase the power of kinship estimation, particularly when combined with additional sequenced single nucleotide polymorphism (SNP) loci, as in the ForenSeq DNA Signature Prep kit. MPS sequencing of ∼10,000 SNPs is available in the ForenSeq Kintelligence kit, promising detection of more distant kin, while SNP chips carrying hundreds of thousands of markers increase resolution still further. Here we evaluate these different resolutions in a set of pedigrees, and via simulations. As expected, the key factor influencing the precision of kinship estimation is the number of markers analysed and MPS-based analysis of STRs increases resolution, with the full set of ForenSeq DNA Signature Prep kit markers allowing detection of third-degree relatives. Since SNP chips include non-autosomal (X- and Y-chromosomal, and mitochondrial [mtDNA]) markers, we ask how these perform within the pedigrees, cross-referencing to Y-STR sequence data. We highlight the importance of understanding haplogroup resolutions in the increasingly complex Y and mtDNA phylogenies, to avoid false exclusions. Incorporation of X-SNPs allows tracing of X-chromosome segments within families. These different approaches can add value to kinship estimation, but some require simpler bioinformatic interfaces to make them more widely accessible in practice, and also access to appropriate allele frequency data to avoid problems associated with ancestry mis-specification.