Countdown to 2017: Internal Validation of the New CODIS Loci


Written by: Carolyn Steffen, Erica Romsos, Michael Coble, and Peter Vallone



The original core set of 13 Combined DNA Index System (CODIS) autosomal short tandem repeat (STR) loci were selected in November 1997 and are required by the Federal Bureau of Investigation (FBI) for upload of DNA profiles to the U.S. national DNA database.  As the number of profiles stored in the National DNA Index System (NDIS) continues to increase each year, the likelihood of adventitious matches becomes greater.  In 2012 the FBI proposed to expand the number of Combined DNA Index System (CODIS) core loci in the United States from 13 to 20 short tandem repeat (STR) loci to reduce the potential of these types of matches occurring within the dataset, to increase international compatibility for data sharing, and to increase discrimination power in missing persons cases.

In November 2009, the European forensic community adopted five new autosomal STR loci as part of their expanded European Standard Set:  D1S1656, D2S441, D10S1248, D12S391, and D22S1045.  These five STR loci are part of the new core U.S. CODIS loci and will provide greater capabilities for international comparisons in the future.  Also, D2S1338 and D19S443 are two new additional STR loci because they are commonly used worldwide as well as in the United States – almost half of the U.S. national database already contains data for these loci.  In addition, the D2S441, D10S1248, and D22S1045 loci were originally characterized at the National Institute of Standards and Technology (NIST) as miniSTR loci that can aid in typing degraded DNA samples.  These seven loci collectively add discrimination to aid in missing persons cases and help reduce the likelihood of adventitious matches in the continuously growing U.S. national DNA database.

Commercial companies have recently released larger STR multiplex kits that enable complete coverage of all of the additional loci for a total of 24 loci in each kit.  These kits include PowerPlex Fusion from Promega, GlobalFiler from Life Technologies, and Investigator 24plex QS from Qiagen.  With the development of these commercial STR multiplex kits containing the proposed expanded loci, a consortium of 11 CODIS laboratories were selected to evaluate the performance of these kits in a collaborative validation study (only PowerPlex Fusion and GlobalFiler were tested for this study – Investigator 24plex QS kit was not included because it was not available in the U.S. until after the study was completed).  In March of 2015, based on the results of the Consortium Validation Study, the FBI published the expansion of the original core 13 loci to a new CODIS core containing 20 loci with an implementation date of January 2017 for U.S. Laboratories.

The need to internally validate new STR multiplex kits has been an on-going process within the forensic DNA community. With the expansion of the core STR loci and release of larger commercial STR multiplex kits, every CODIS participating laboratory in the U.S. must validate one of these kits in less than two years.  The Applied Genetics Group at NIST is presenting a workshop at the International Symposium on Human Identification (ISHI) to introduce the new required loci beyond the original core set and discuss the design and analysis of internal validation experiments (including known and non-probative samples, precision and accuracy, contamination, sensitivity and stochastic, and mixture analysis studies).  Examples of analysis and interpretation challenges using real validation data will be presented throughout the workshop.

It is our intention for this workshop to be a general guide and thought provoking forum for the planning and execution of an internal validation.  It is not our intention for our design to be the “standard” internal validation protocol but rather to explain the important components and discussions that are part of the planning of an internal validation.