OSAC 2021‐S‐0029

Standard for Familial DNA

Searching

Human Forensic Biology Subcommittee

Biology Scientific Area Committee (SAC)

Organization of Scientific Area Committees (OSAC) for Forensic Science
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OSAC Proposed Standard

OSAC 2021‐S‐0029

Standard for Familial DNA Searching

Prepared by  

Human Forensic Biology Subcommittee

Version: 2.1

December 2023

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

https://www.nist.gov/topics/organization‐scientific‐area‐committees‐forensic‐

science/scientific‐technical‐review‐panels.  

Version

No.

Issue Date Section Reason

2.0 January 5, 2023  ‐‐  Added to the OSAC Registry and publicly announced.

2.1 December 28, 2023 All Format and font updates only. No content changes made.

   
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Table of Contents

1 Scope .....................................................................................................................................5

2 Normative References........................................................................................................... 5

3 Terms and Definitions............................................................................................................ 5

4 Requirements ........................................................................................................................ 6

Annex A.......................................................................................................................................11

   

   
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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

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.
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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

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 familialsearchesthat 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 thatshall 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 documentshall define the processfor 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;  
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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):  

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.
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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.

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

relatives(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.  

4.2 Technical  

4.2.1 The laboratory shall use validated analytical procedures/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 LRsfor 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
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4.2.3.3 silent (null) allele model

4.2.3.4 correction of linkage

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 the 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 itsimplicationsfor 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.