Kinship Inferences for Second-Degree Relatives With a Combination of STRs and Microhaplotypes

This study evaluated kinship identification using 19 short tandem repeats (STRs) from AGCU EX22 kit, 119 microhaplotypes (52 in Panel A + 67 in Panel B), and a theoretical 9622 genome-wide single nucleotide polymorphisms (SNPs) panel (The 9K). The system power was assessed accounting for linkage on the basis of 198 Chinese Southern Han (CHS) family samples and simulated data. STR + Panels A and B distinguished full-sibling (FS) from unrelated (un), with second-degree effectiveness above 0.96 when log₁₀(LR) threshold was 4 and low false positive rate (<0.06%), but were insufficient for more distant kinship identification alone. The 9K panel was sufficient to separate third-degree from un but not for fourth-degree or more distant relatives. For discrimination among different kinships, STR + Panels A and B successfully distinguished all FS from half-siblings (HS), uncle/aunt-nephew/niece (UN), and grandparents-grandson/granddaughter (GS) in real data, with minimal overlaps (<0.2%). Discriminating second- and third-degree or within second-degree relatives seems very challenging, even for 9K panel. Including a carefully selected additional relative (AR) may improve discrimination between GS and UN/HS, such as AR (GS-un, which is GS for one person and un for the other) and AR (parent/child (PC)-UN). Similarly, an AR (PC-GS) may help distinguish UN from GS/HS, but there was slightly improved efficiency for HS.