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Study Objective. To determine long-term stability, quantity, and quality of genomic DNA samples collected in buccal cells by the mouthwash method, for use in pharmacogenetic studies.

Design. Prospective analysis.

Setting. University pharmacogenomics center in Florida and medical centers in Puerto Rico and the United States participating in a multicenter international trial.

Subjects. Ten volunteers at the pharmacogenomics center and 201 participants in the ongoing multicenter clinical trial.

Intervention. Stability of genomic DNA was determined by measuring DNA yield from mouthwash samples obtained from six volunteers and stored at room temperature over 90 days and from 201 clinical trial samples that were stored and shipped at room temperature. Whether DNA yield was higher with three 5–ml mouthwash rinses versus one 10–ml rinse was evaluated in four volunteers. Quality of genomic DNA was assessed on 32 randomly selected samples from the six volunteers in the stability study, by determining the success rate of DNA amplification with polymerase chain reaction (PCR) testing and by genotyping.

Measurements and Main Results. For the stability studies, the quantity of genomic DNA decreased over time with storage at room temperature (overall p<0.01), with the largest declines occurring at 60 and 90 days. Median DNA recovery at 30 and 90 days was 59% and 28% of that at baseline, respectively. Mean ± standard deviation, median, and range for recovery of genomic DNA from the 201 samples were 45.2 ± 55 μg, 25.2 μg, and 1–330 μg, respectively. Median recoveries of DNA from the one-rinse and three-rinse methods were not statistically significantly different (9.1 vs 10.5 μg). All samples were amplified successfully by PCR and genotyped, indicating quality of the DNA samples.

Conclusion. The mouthwash method for collection of genomic DNA is a simple, inexpensive, and noninvasive method that poses less risk than venipuncture and may be used in a variety of settings. Genomic DNA in mouthwash is stable for prolonged periods at room temperature, and the quantity of DNA recovered from this method is more than sufficient for pharmacogenetic studies. Such an approach should be valuable to pharmacogenetic researchers and others who are conducting genetic research.