OSAC 2021-S-0029 Standard for Familial DNA Searching

OSAC 2021-S-0029

Standard for Familial 

DNA Searching

Forensic Human Biology Subcommittee

Biology Scientific Area Committee 

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

OSAC Proposed Standard

OSAC 2021-S-0029

Standard for Familial DNA Searching 

Prepared by 

Human Forensic Biology Subcommittee

Version: 2.0

November 2022

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

Table of Contents

1. 12.

13.

14.

2

2

5Annex A

7
OSAC 2021-S-0029 Standard for Familial DNA Searching

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Standard for Familial DNA Searching

1. Scope

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

written policy specifying criteria for:

a) accepting a familial DNA search request;

b) administrative structure and responsibilities; 

c) the search process; 

d) reporting results; and

e) safeguarding individual privacy and confidentiality of the results.

This standard also defines validation requirements.

Note: This standard does not apply to Investigative Genetic Genealogy or to the 

investigation of partial matches that may occur during the normal course of forensic 

database searches.

2. Normative References

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

references.

3. Terms and Definitions

For the purposes of this document the following definitions apply:

3.1

familial DNA search

familial DNA searching 

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

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

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

3.2

likelihood ratio (LR)

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

probability of the evidence under an alternative, mutually exclusive proposition 

(hypothesis). The magnitude of its value expresses the weight of the evidence.

3.3

likelihood ratio threshold

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

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

to investigate only those candidates above a certain likelihood ratio. 

3.4

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

maternal or paternal inheritance. 

3.5

ranking threshold

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

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

to investigate only a set number of the best ranked candidates regardless of the 

likelihood ratio. 

3.6

sensitivity study

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

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

database.

3.7 

specificity study

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

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

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

4. Requirements

4.1 Policy and Procedure: The laboratory shall have documented policies and/or

procedures for conducting familial DNA searching that shall contain the information 

detailed in 4.1.1 through 4.1.11, as applicable to the laboratory’s involvement in the 

elements described in each substandard. To aid the public and law enforcement in 

understanding the laboratory’s familial search results, the familial search policy should be 

publicly available.

4.1.1 The document shall define the process for case submission and acceptance for 

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

acceptance policy:

a) seriousness or seriality of the crime;

b) commitment to proceed with investigation and prosecution;

c) case metadata and laboratory notes provided as available;

d) investigative stage to initiate a familial search, such as, when other apparently 

viable investigative strategies have been exhausted;

e) the availability of additional DNA evidence; and

f) out of state search requests.

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

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

individuals in the following roles (an individual may fill more than one role):
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a) a review committee (e.g. to evaluate requests, prioritize testing, verify results, 

and determine the propriety of moving forward with an investigation or 

disclosure of a name);

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

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

c) an administrative representative from the source testing laboratory;

d) an administrative representative from the searching laboratory;

e) a technical representative from the source testing laboratory;

f) a technical representative from the searching laboratory;

g) a representative with access to investigative databases (metadata) typically 

restricted to law enforcement personnel;

h) a representative from the requesting law enforcement agency;

i) a representative from the prosecuting agency; and

j) a representative of the defendant when the search is being performed at the 

request of the defense.

4.1.3 The document shall define how information obtained through the familial search 

process is shared and released and should include: 

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

and 

b) Provisions protecting the privacy of possible family members in the search 

database who could not be the perpetrator.

4.1.4 The document shall ensure that all the individuals with roles established in 4.1.2 are 

informed of the process, likely outcomes, limitations, and the need for additional 

investigation. This could be achieved through the use of a documented 

memorandum of understanding or equivalent.

4.1.5 The document shall address the collection, testing, and retention/destruction of the 

following comparison samples:

4.1.5.1 surreptitiously collected samples associated with the person of 

interest

4.1.5.2 samples known not to be from the perpetrator but that could provide 

additional confirmatory information (e.g. possible relatives of the 

perpetrator), whether collected surreptitiously or voluntarily 
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4.1.5.3 confirmatory samples, which are direct reference samples from a 

person of interest that are collected with a chain of custody

4.1.6 The document shall define the acceptance requirements of the evidence profile to be 

searched to include the information in 4.1.6.1 through 4.1.6.5. 

4.1.6.1 That the DNA sample was recovered directly from the crime scene (or 

associated to the crime scene) and is attributed to the putative 

perpetrator.

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

profile rarity.

4.1.6.3 The acceptable level of potential allelic dropout in the profile 

submitted for the familial DNA search.

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

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

number of contributors.

4.1.6.5 A requirement that a direct comparison search of the profile has 

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

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

4.1.7 The document shall define which database categories will be searched (e.g. 

convicted offenders, arrestees, suspects).

4.1.8 The document shall define which relationships (e.g., 1st degree relatives only) will 

be considered.

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

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

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

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

4.1.10 The document shall define the thresholds (e.g. likelihood ratio and/or ranking) for 

proceeding with the release of information regarding potential relatives.

4.1.11 The document shall define the criteria for the release of the name(s) of the potential 

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

name(s) of the potential relative(s):

a) The use of metadata for the evaluation of a potential relative.

b) Assessing kinship using non-invasive investigation, i.e., one that does 

not require direct contact with a person of interest.
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4.2 Technical

4.2.1 The laboratory shall use validated 

analyticalprocedures/systems and software.

4.2.2 Internal validation shall include sensitivity and specificity 

studies to include the range of search profiles defined in 

4.1.6.2, 4.1.6.3, and 4.1.6.4.

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

process with a meaningfully sized dataset when the process includes extensive 

additional testing and investigative work.

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

profiles of true relatives (at a minimum, those defined in section 4.1.9) of the 

experimental search profile. Ranking the LRs for all comparisons from highest to 

lowest, sensitivity is defined as the proportion of true relatives (real or in silico) 

included at each rank. Alternatively, the ranked list of unrelated individuals’ LRs could 

be seeded with the LRs for each of the true family members, thus avoiding the 

insertion of experimental profiles into the database.

A reasonable specificity test would examine how many individuals remain as 

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

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

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

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

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

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

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

Search criteria developed from sensitivity and specificity studies should be established 

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

probability of releasing reliable leads.

Search criteria developed from sensitivity and specificity studies can be impacted by 

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

being searched. 

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

4.2.3.1 population substructure (Fst or theta)

4.2.3.2 mutation model

4.2.3.3 silent (null) allele model

4.2.3.4 correction for linkage
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4.2.3.5 probabilistic genotyping

4.2.3.6 prior odds

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

searching including training in kinship analysis.

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

concepts.

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

i. the flow of DNA through pedigrees; and

ii. lineage vs. autosomal patterns of inheritance

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

i. likelihood ratios; and

ii. conditional probabilities given an assumed level of relatedness

c). Likelihood ratio distributions for various relationship categories.

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

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

f). The effect of population database selection on the likelihood ratio.

g). The effect of database size on the ranking of true relatives.

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

(informative)

Bibliography

The following information provides a list of literature resources.

1) Ayres, K.L. “Relatedness testing in subdivided populations.” Forensic Science 

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

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

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

paternity.” Genetica vol. 96, 1995, pp. 3–12.

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

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

paternity.” Genetica vol. 133, 2008, pp. 107.

4) Bieber, F.R. et al. “Finding Criminals Through DNA of Their Relatives.” Science

vol. 312, issue 5778, 2006, pp. 1315-1316.

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

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

380-383. 

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

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

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

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

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

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

utilizing the National DNA Database to identify unknown offenders via their 

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

2014, pp. 1-9.

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

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

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

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

for Implementation.” Investigative Science Journal, vol. 9, no. 4, 2017.
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11) Rohlfs, R.V. et al. “Familial Identification: Population Structure and Relationship 

Distinguishability.” PLoS Genetics, vol. 8(2), 2012, e1002469.

12) Rohlfs, R.V. et al. “The Influence of Relatives on the Efficiency and Error Rate of 

Familial Searching.” PLoS ONE, vol. 8(8), 2013, e70495.

13) SWGDAM. Recommendations from the SWGDAM Ad Hoc Working Group on 

Familial Searching. It is available at: 

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

14) Slooten, K. “Familial searching on DNA mixtures with dropout.” Forensic Science 

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

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

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