PCR Amplification and Typing of the HLA DQα Gene in Forensic Samples

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Abstract
The polymerase chain reaction (PCR) was used to amplify the HLA DQα gene using DNA recovered from evidentiary samples. Amplified HLA DQα DNA was then typed using sequence-specific oligonucleotide probes. Slight modifications of previously published DNA extraction methods improved typing success of bloodstains and semen-containing material. Evidentiary samples, consisting of 206 known bloodstains, 26 questioned bloodstains, and 123 questioned semen-containing evidentiary materials were analyzed from 96 cases previously analyzed by restriction fragment length polymorphism (RFLP) typing in the FBI Laboratory. Of the known bloodstains, 98.5% yielded DQα typing results. Of the questioned samples, 102 of 149 (24/26 bloodstains and 78/123 semen-containing materials), or 68%, produced typing results. Of the 78 cases that were RFLP inclusions, 59 yielded interpretable DQα results and these were all inclusions. The remaining 19 cases could not be interpreted for DQα. Of the 18 RFLP exclusions, eleven were DQα exclusions, four were DQα inclusions, and three could not be interpreted for DQα. It is expected that because of the difference in discrimination potential of the two methods, some RFLP exclusions would be DQα inclusions. Some samples that failed to produce typing results may have had insufficient DNA for analysis. Employment of a human DNA quantification method in DQα casework would allow the user to more consistently use sufficient quantities of DNA for amplification. It also could provide a guide for determining if an inhibitor of PCR is present, thus suggesting the use of a procedure to improve amplification. This study provides support that the HLA DQα typing procedure is valid for typing forensic samples.