Analysis of Kinship Index Distributions in Koreans Using Simulated Autosomal STR Profiles

In Seok Yang; Hwan Young Lee; Su Jeong Park; Woo Ick Yang; Kyoung-Jin Shin

doi:10.7580/kjlm.2013.37.2.57

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Yang, Lee, Park, Yang, and Shin: Analysis of Kinship Index Distributions in Koreans Using Simulated Autosomal STR Profiles

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Korean J Leg Med 2013;37(2):57-65.

Published online: 17 January 2013

DOI: https://doi.org/10.7580/kjlm.2013.37.2.57

Analysis of Kinship Index Distributions in Koreans Using Simulated Autosomal STR Profiles

In Seok Yang¹, Hwan Young Lee¹, Su Jeong Park², Woo Ick Yang¹, Kyoung-Jin Shin¹

¹Department of Forensic Medicine, Yonsei University College of Medicine, Seoul, Korea

²DNA Analysis Laboratory, DNA Forensic Division, Supreme Prosecutors’ Office, Seoul, Korea

이 논문은 2012년도 대검찰청의 DNA감식 기술의 국산화 및 선진화 연구사업의 지원 을 받아 수행된 연구임(1333-304). 책임저자 : 신경진 (120-752) 서울시 서대문구 연세로 50 연세대학교 의과대학 법의학과 전화 : +82-2-2228-2481 FAX : +82-2-362-0860 E-mail : kjshin@yuhs.ac

Received 29 April 2013 Accepted 21 May 2013

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Kinship testing in forensic casework is largely based on a likelihood ratio (LR) approach with short tandem repeat (STR) markers; however, in order to efficiently identify potential relatives in a specific population, the threshold values for kinship prediction should be determined by analyzing the kinship index distributions of the population in question. In this study, 250,000 DNA profiles were simulated using allele frequencies at 20 autosomal STR loci in Koreans, then the LRs were calculated for true close relatives and unrelated pairs. The LR distributions in related and unrelated pairs under a given relationship were compared in 2 sets of 13 Combined DNA Index System (CODIS) and 20 STR profiles. Using 13 CODIS STRs, true relatives in parent/child and full-sibling relationships were sufficiently discriminated from unrelated pairs with LR thresholds of 1,000 and 100, respectively. However, the CODIS STRs lacked the discriminatory power to differentiate between related and unrelated pairs in uncle/nephew and first cousin relationships due to high false-positive and false-negative rates with a LR threshold of 10. Increasing the number of STR loci to 20 increased discrimination of close relatives, but high false results remained in uncle/nephew and first cousin relationships. The kinship index data from this study will help make decisions on various kinship testing and familial searching in Koreans.

Keywords: Key Words, STR, Kinship index, Simulation, Familial searching, Koreans

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Fig. 1.

Virtual pedigree constructed by simulated autosomal STR profiles in this study.

Fig. 2.

Likelihood ratio distributions for parent/child relationship with 13 (a) and 20 autosomal STR loci (b). Red and orange lines represent related distributions. Blue and skyblue lines indicate unrelated distributions.

Fig. 3.

Likelihood ratio distributions for full-siblings relationship with 13 (a) and 20 autosomal STR loci (b). Red and orange lines represent related distributions. Blue and skyblue lines indicate unrelated distributions.

Fig. 4.

Likelihood ratio distributions for uncle/nephew relationship with 13 (a) and 20 autosomal STR loci (b). Red and orange lines represent related distributions. Blue and skyblue lines indicate unrelated distributions.

Fig. 5.

Likelihood ratio distributions for first cousins relationship with 13 (a) and 20 autosomal STR loci (b). Red and orange lines represent related distributions. Blue and skyblue lines indicate unrelated distributions.

Table 1.

Log₁₀ (Median Likelihood Ratio) Values for Each Relationship in Koreans

	No. of STRs	Relationship
	No. of STRs	Parent/Child	Full-siblings	Uncle/Nephew	First cousins
Related	13	-3.90 ± 0.01	-3.30 ± 0.00	-0.86 ± 0.00	-0.20 ± 0.00
Related	20	-6.31 ± 0.01	-5.30 ± 0.01	-1.41 ± 0.01	-0.35 ± 0.00
Unrelated	13	-0.83 ± 0.06	-2.76 ± 0.01	-0.83 ± 0.00	-0.23 ± 0.00
Unrelated	20	-0.36 ± 0.48	-4.34 ± 0.01	-1.32 ± 0.00	-0.36 ± 0.00

Table 2.

False-positive and False-negative Rates on Kinship Index (KI) Distributions for Each Relationship

No. of STRs	Threshold	False-positive rate (%)
No. of STRs	KI	Parent/Child	Full-siblings	Uncle/Nephew	First cousins
13	1	0.213 ± 0.005	2.951 ± 0.040	15.656 ± 0.137	28.455 ± 0.189
	10	0.126 ± 0.016	0.562 ± 0.029	1.457 ± 0.039	0.392 ± 0.027
	100	0.071 ± 0.013	0.090 ± 0.008	0.056 ± 0.014	0.002 ± 0.002
	1,000	0.019 ± 0.008	0.010 ± 0.006	0.000 ± 0.000	0.000 ± 0.000
	10,000	0.002 ± 0.003	0.000 ± 0.001	0.000 ± 0.000	0.000 ± 0.000
	100,000	0.000 ± 0.000	0.000 ± 0.000	0.000 ± 0.000	0.000 ± 0.000
20	1	0.015 ± 0.004	0.856 ± 0.047	10.176 ± 0.114	24.248 ± 0.157
	10	0.006 ± 0.004	0.166 ± 0.017	1.348 ± 0.077	0.757 ± 0.047
	100	0.002 ± 0.001	0.025 ± 0.009	0.084 ± 0.013	0.006 ± 0.004
	1,000	0.001 ± 0.001	0.003 ± 0.002	0.002 ± 0.002	0.000 ± 0.000
	10,000	0.000 ± 0.001	0.001 ± 0.001	0.000 ± 0.000	0.000 ± 0.000
	100,000	0.000 ± 0.000	0.000 ± 0.000	0.000 ± 0.000	0.000 ± 0.000
No. of STRs	Threshold KI	False-negative rate (%)
No. of STRs	Threshold KI	Parent/Child	Full-siblings	Uncle/Nephew	First cousins
13	1	0.000 ± 0.000	3.374 ± 0.045	16.865 ± 0.067	33.170 ± 0.211
	10	0.059 ± 0.010	10.496 ± 0.069	56.012 ± 0.106	92.333 ± 0.103
	100	2.193 ± 0.037	24.353 ± 0.273	87.720 ± 0.187	99.374 ± 0.012
	1,000	18.428 ± 0.095	43.853 ± 0.139	97.750 ± 0.091	99.950 ± 0.010
	10,000	53.511 ± 0.264	64.384 ± 0.189	99.684 ± 0.028	99.998 ± 0.002
	100,000	82.622 ± 0.166	81.030 ± 0.134	99.973 ± 0.006	100.000 ± 0.000
20	1	0.000 ± 0.000	1.026 ± 0.025	10.933 ± 0.117	27.921 ± 0.303
	10	0.000 ± 0.001	3.116 ± 0.115	36.296 ± 0.204	83.170 ± 0.096
	100	0.008 ± 0.004	7.870 ± 0.114	68.610 ± 0.175	98.028 ± 0.044
	1,000	0.265 ± 0.028	16.444 ± 0.123	89.549 ± 0.104	99.787 ± 0.022
	10,000	3.084 ± 0.082	29.145 ± 0.121	97.460 ± 0.058	99.984 ± 0.002
	100,000	15.639 ± 0.133	44.950 ± 0.206	99.484 ± 0.012	99.999 ± 0.001

Table 3.

Log₁₀ (Median Likelihood Ratio) Values for Each Relationship in US Caucasian⁶⁾

	No. of STRs	Relationship
	No. of STRs	Parent/Child^∗	Full-siblings	Half-siblings^†
Related	13	-04.00	-3.38	-0.84
Related	20	-06.95	-5.83	-1.51
Unrelated	13	-16.57	-2.82	-0.85
Unrelated	20	-	-4.62	-1.44

^∗ Possible mutation in unrelated pairs identified as parent/child was differently treated on kinship index calculation compared with the case of this study (see http://dna-view.com/mudisc.htm).

^† Half-siblings relationship is genetically identical with uncle/nephew relationship.

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