OSAC 2021-S-0029 - Standard for Familial DNA Searching

OSAC 2021-S-0029

Standard for Familial 

DNA Searching

Forensic Human Biology Subcommittee

Biology SAC

Organization of Scientific Area Committees (OSAC) for Forensic Science
OSAC 2021-S-0029 - Standard for Familial DNA Searching

Draft OSAC Proposed Standard

OSAC 2021-S-0029

Standard for Familial DNA Searching 

Prepared by 

Human Forensic Biology Subcommittee

Version: 1.0

August 2021

Disclaimer:

This OSAC Proposed Standard was written by the Human Forensic Biology Subcommittee of the 

Organization of Scientific Area Committees (OSAC) for Forensic Science following a process that 

includes an open comment period. This Proposed Standard will be submitted to a standards developing 

organization and is subject to change.

There may be references in an OSAC Proposed Standard to other publications under development by 

OSAC. The information in the Proposed Standard, and underlying concepts and methodologies, may be 

used by the forensic-science community before the completion of such companion publications.

Any identification of commercial equipment, instruments, or materials in the Proposed Standard is not a 

recommendation or endorsement by the U.S. Government and does not imply that the equipment, 

instruments, or materials are necessarily the best available for the purpose.

To be placed on the OSAC Registry, certain types of standards first must be reviewed by a Scientific and 

Technical Review Panel (STRP). The STRP process is vital to OSAC’s mission of generating and 

recognizing scientifically sound standards for producing and interpreting forensic science results. The 

STRP shall provide critical and knowledgeable reviews of draft standards or of proposed revisions of 

standards previously published by standards developing organizations (SDOs) to ensure that the 

published methods that practitioners employ are scientifically valid, and the resulting claims are 

trustworthy.

The STRP panel will consist of an independent and diverse panel, including subject matter experts, 

human factors scientists, quality assurance personnel, and legal experts, which will be tasked with 

evaluating the proposed standard based on a comprehensive list of science-based criteria.

For more information about this important process, please visit our website

at: https://www.nist.gov/topics/organization-scientific-area-committees-forensic-science/scientifictechnical-review-panels. 
OSAC 2021-S-0029 - Standard for Familial DNA Searching

1 Table of Contents

2

3 1. 12.

4 13.

5 14.

6 2

7 2

8 4Annex A

9 5

10
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Standard for Familial DNA Searching

11 Standard for Familial DNA Searching

12 1. Scope

13 This standard requires laboratories that perform familial DNA searches to have a 

14 written policy with criteria for:

15 a) accepting a familial DNA search request, administrative structure, and 

16 responsibilities; 

17 b) the search process, data verification, and validation; 

18 c) reporting results; and

19 d) safeguarding individual privacy and confidentiality of the results.

20 2. Normative References

21 The document contains no normative references. See Annex A, Bibliography for other 

22 references.

23 3. Terms and Definitions

24 For the purposes of this document the following definitions apply:

25 3.1

26 familial DNA search

27 familial DNA searching 

28 A deliberate search of a DNA database using software to detect and statistically rank a 

29 list of potential candidates in the database who may be close biological relatives (e.g. 

30 parent, child, sibling) to the unknown individual contributing the evidence DNA profile. 

31 3.2

32 likelihood ratio (LR)

33 The probability of the evidence under one proposition (hypothesis), divided by the 

34 probability of the evidence under a mutually exclusive proposition (hypothesis). The 

35 magnitude of its value expresses the weight of the evidence.

36

37 3.3

38 likelihood ratio threshold

39 The likelihood ratio below which a database profile specific to the relationship(s) under 

40 consideration would not be further investigated. For example, a laboratory may decide 

41 to investigate only those candidates above a certain likelihood ratio. 

42

43 3.4

44 lineage testing

45 Genetic testing, such as YSTR, XSTR, or mitochondrial DNA analysis, used to trace 

46 maternal or paternal inheritance. 

47 3.5

48 ranking threshold

49 The rank below which a database profile specific to the relationship(s) under 

50 consideration would not be further investigated. For example, a laboratory may decide 
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51 to investigate only a set number of the best ranked candidates regardless of the 

52 likelihood ratio. 

53 3.6

54 sensitivity study

55 An assessment of the proportion of familial searches that detect true relatives of the 

56 contributor of the evidence profile when one or more relatives is present in the 

57 database.

58 3.7 

59 specificity study

60 An assessment of the proportion of familial searches that exclude non-relatives of the 

61 contributor of the evidence profile. Practical limitations may restrict this study to the 

62 initial statistical comparisons of simulated forensic unknowns to DNA database profiles.

63 4. Requirements

64 4.1 Policy and Procedure: The laboratory shall have documented policies and procedures for 

65 conducting familial DNA searching that shall contain the information detailed in 4.1.1 through 4.1. 

66 To aid the public and law enforcement in understanding the laboratory’s familial search results, the 

67 familial search policy should be publicly available.

68 4.1.1 The policy shall define the process for case submission and acceptance for 

69 conducting DNA familial searching. The following may be considered in the case 

70 acceptance policy:

71 a) seriousness or seriality of the crime;

72 b) commitment to proceed with investigation and prosecution;

73 c) case metadata and laboratory notes provided as available;

74 d) investigative stage to initiate a familial search, such as, when viable reasonable; 

75 investigative strategies have been exhausted; and

76 e) the availability of additional DNA evidence.

77 4.1.2 The policy shall define the roles of the individuals involved in the DNA familial 

78 search process and oversight. The familial DNA search process may involve 

79 individuals in the following roles:

80 a) an individual or committee who has the ultimate control for the search and 

81 directs the release of investigative lead(s) and any follow-up;

82 b) an administrative representative from the source testing laboratory;

83 c) an administrative representative from the searching laboratory;

84 d) a technical representative from the source testing laboratory;

85 e) a technical representative from the searching laboratory;
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86 f) a review committee (e.g. to evaluate requests, prioritize testing, verify results, 

87 and determine the propriety of moving forward with an investigation or 

88 disclosure of a name);

89 g) a representative with access to investigative databases (metadata) restricted to 

90 law enforcement personnel;

91 h) a representative from the requesting law enforcement agency; and

92 i) a representative from the prosecuting agency.

93 4.1.3 The policy shall define the interactions between the individuals defined in 4.1.2 so 

94 as to safeguard privacy. The policy may include the use of a documented 

95 memorandum of understanding or equivalent.

96 4.1.4 The policy shall define how information obtained through the familial search 

97 process is shared and released and should include: 

98 a) Safeguards for the disclosure of sensitive information to the proper individuals; 

99 and 

100 b) Provisions protecting the privacy of those family members who could not be the 

101 perpetrator.

102 4.1.5 The policy shall ensure that all the individuals defined in 4.1.2 are informed of the 

103 process, likely outcomes, limitations, and the need for additional investigation.

104 4.1.6 The policy shall address the collection and testing of the following comparison 

105 samples:

106 4.1.6.1 surreptitiously collected samples associated with the person of 

107 interest

108 4.1.6.2 samples known not to be the perpetrator but may provide additional 

109 confirmatory information (e.g. possible relatives of the perpetrator), 

110 whether collected surreptitiously or voluntarily 

111 4.1.6.3 confirmatory samples 

112 4.1.7 The policy shall define the acceptance requirements of the evidence profile to be 

113 searched to include the information in 4.1.7.1 through 4.1.7.5. 

114 4.1.7.1 That the DNA sample was recovered directly from the crime scene 

115 and is attributed to the putative perpetrator.

116 4.1.7.2 The minimum threshold for the number of searchable loci and/or 

117 profile rarity
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118 4.1.7.3 The acceptable level of potential allelic dropout in the profile 

119 submitted for the familial DNA search

120 4.1.7.4 The number of possible contributors, e.g. single source, deduced 

121 single source from a mixture, or mixtures up to a defined maximum 

122 number of contributors

123 4.1.7.5 A requirement that a direct comparison search of the profile has 

124 occurred in relevant databases (e.g., Combined DNA Index System 

125 (CODIS)) prior to the familial DNA search being conducted. 

126 4.1.8 The policy shall define which database categories will be searched (e.g. convicted 

127 offenders, arrestees, suspects).

128 4.1.9 The policy shall define which relationships will be considered.

129 4.1.10 When possible, the laboratory shall conduct expanded autosomal STR (beyond the 

130 original 13 CODIS core loci) and/or lineage testing (e.g. YSTR, XSTRs and/or 

131 mitochondrial DNA) of potential relatives. The laboratory shall document situations 

132 where, and justify conditions when conducting additional testing is not required. 

133 4.1.11 The policy shall define the thresholds (e.g. likelihood ratio and/or ranking) for 

134 proceeding with the release of information regarding potential relatives.

135 4.1.12 The policy shall define the criteria for the release of the name(s) of the potential 

136 relative(s). The following criteria may be considered prior to the release of the 

137 name(s) of the potential relative(s).

138 4.1.12.1 The use of metadata for the evaluation of a potential relative

139 4.1.12.2 Assessing kinship using non-invasive investigation

140 4.2 Technical

141 4.2.1 The laboratory shall use validated analytical procedures/systems 

142 and software.

143 4.2.2 Internal validation shall include sensitivity and specificity studies.

144 It is impractical to perform both sensitivity and specificity studies on the entire 

145 process with a meaningfully sized dataset when the process includes extensive 

146 additional testing and investigative work.

147 A reasonable sensitivity test would seed a database of unrelated individuals with the

148 profiles of true relatives of the experimental search profile. Ranking the LRs for all 

149 comparisons from highest to lowest, sensitivity is defined as the proportion of true 

150 relatives (real or in silico) included at each rank. Alternatively, the ranked list of 
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151 unrelated individuals’ LRs could be seeded with the LRs for each of the true family 

152 members, thus avoiding the insertion of experimental profiles into the database.

153 A reasonable specificity test would examine how many individuals remain as 

154 candidates after the statistical process (e.g., the initial LR rankings based solely upon 

155 autosomal STR loci). Coupled with how many of those individuals would meet the 

156 requirements to be tested with additional lab work, this will give an estimate of how 

157 likely it would be to see a false positive. Knowing whether the statistical process the 

158 lab has put in place will lead to tens of candidates, hundreds of candidates, or 

159 thousands of candidates will give a sense of whether or not the subsequent lineage 

160 testing (or additional autosomal markers) might adventitiously include a non-relative.

161 Search criteria developed from sensitivity and specificity studies should be established 

162 to err on the side of minimizing false positives. This approach will enhance the 

163 probability of releasing reliable leads.

164 Search criteria developed from sensitivity and specificity studies may be impacted by 

165 the capacity and resources of the laboratory in addition to the size of the database 

166 being searched. 

167 4.2.3 The laboratory shall determine if the process will incorporate the following:

168 4.2.3.1 mutation model

169 4.2.3.2 silent (null) allele model

170 4.2.3.3 correction for linkage

171 4.2.3.4 probabilistic genotyping

172 4.2.4 The laboratory shall have a documented training program specific to familial DNA 

173 searching including training in kinship analysis.

174 Training of an individual evaluating familial search results should include the following 

175 concepts.

176 a). The expected levels of DNA sharing for various relationships, including:

177 i. the flow of DNA through pedigrees; and

178 ii. lineage vs. autosomal patterns of inheritance

179 b). The calculations performed in familial searching, including:

180 i. likelihood ratios; and

181 ii. conditional probabilities given an assumed level of relatedness

182 c). Likelihood ratio distributions for various relationship categories.

183 d). Evaluating pedigrees larger than two-person comparisons.

184 e). Addressing the issues of linked loci and meiotic mutations.

185 f). The effect of population database selection on the likelihood ratio.
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186 g). The effect of database size on the ranking of true relatives.

187 h). The benefits and limitations of lineage vs. autosomal loci. 

188
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189 Annex A

190 (informative)

191

192 Bibliography

193 The following information provides a list of literature resources.

194 1) Ayres, KL. “Relatedness testing in subdivided populations.” Forensic Science 

195 International, vol. 114, 2000, pp. 107-115.

196

197 2) Balding, D.J., Nichols, R.A. “A method for quantifying differentiation between 

198 populations at multi-allelic loci and its implications for investigating identity and 

199 paternity.” Genetica vol. 96, 3–12 (1995).

200

201 3) Balding, D.J., Nichols, R.A. “A method for quantifying differentiation between 

202 populations at multi-allelic loci and its implications for investigating identity and 

203 paternity.” Genetica vol. 133, 107 (2008).

204

205 4) Bright, J-A et al. “Relatedness calculations for linked loci incorporating 

206 subpopulation effects.” Forensic Science International: Genetics, vol. 7, 2013, 

207 pp.380-383. 

208

209 5) Bright, J-A et al. “Corrigendum to ‘Relatedness calculations for linked loci 

210 incorporating subpopulation effect’ [Forensic Sci. Int: Genet., 7 (2013), 380-

211 383].” Forensic Science International: Genetics, vol 7, 2013, p. 565.

212

213 6) Kruijver M et al. “Optimal strategies for familial searching.” Forensic Science 

214 International: Genetics, vol. 13, 2014, pp. 90-103.

215

216 7) Maguire CN et al. “Familial searching: A specialist forensic DNA profiling service 

217 utilizing the National DNA Database to identify unknown offenders via their 

218 relatives – The UK experience.” Forensic Science International: Genetics, vol. 8, 

219 2014, pp. 1-9.

220

221 8) Myers SP et al. “Searching for first-degree familial relationships in California’s 

222 offender DNA database: Validation of a likelihood ratio-based approach.” 

223 Forensic Science International: Genetics, vol. 5, 2011, pp. 493-500.

224

225 9) Murray A et al. “Familial DNA Testing: Current Practices and Recommendations 

226 for Implementation.” Investigative Science Journal, vol. 9, no. 4, September 2017.

227
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228 10) SWGDAM. Recommendations from the SWGDAM Ad Hoc Working Group on 

229 Familial Searching. It is available at: 

230 http://media.wix.com/ugd/4344b0_46b5263cab994f16aeedb01419f964f6.pdf)

231

232 11) Slooten, K. Familial searching on DNA mixtures with dropout. Forensic Science 

233 International: Genetics, vol 22, 2016, pp.128-138.

234

235 12) Wenke, RE et al. “Determination of sibship of any two individuals.”, Transfusion, 

236 vol. 26, no. 3, 1996, pp. 259-262.