Evaluation of the long-term storage stability of saliva as a source of human DNA

The objectives of this paper are to determine the storage stability of saliva at 37 A degrees C over an 18-month period, and its influence on the DNA yield, purity, PCR protocols and genotyping efficacy. Of the 60 participants, blood samples were obtained from 10 and saliva from 50. Samples were subjected to different storage conditions: DNA extracted immediately; DNA extracted following storage at 37 A degrees C for 1, 6, 12 and 18 months. Subsequently, DNA yield, OD260/280 and OD260/230 ratios were measured. The isolated DNA was used to amplify exons 0-7 of the RUNX2 gene and subsequently sequenced. Furthermore, 25 SNPs were genotyped. The mean DNA yield, OD260/280 and OD260/230 ratios obtained from blood were 67.4 ng/mu l, 1.8 +/- 0.05 and 1.8 +/- 0.4 respectively. DNA yield obtained from saliva was significantly higher than blood (p < 0.0001), ranging from 97.4 to 125.8 ng/mu l while the OD260/280 ratio ranged from 1.8 +/- 0.13 to 1.9 +/- 0.1. The success rates for the 25 SNPs ranged from 98 to 100 % for blood and 96-99 % for saliva samples with the genotype frequencies in Hardy-Weinberg equilibrium (> 0.01). Saliva can be stored at 37 A degrees C for 18 months without compromising its quality and ability to endure genetic analyses. Saliva is a viable source of human DNA to facilitate the feasibility of large-scale genetic studies.