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Open Access Open Badges Technical Note

Using a commercially available DNA extraction kit to obtain high quality human genomic DNA suitable for PCR and genotyping from 11-year-old saliva saturated cotton spit wads

Erik A Ehli1, Timea Lengyel-Nelson1, James J Hudziak2 and Gareth E Davies134*

Author Affiliations

1 Avera Institute for Human Behavioral Genetics, Avera Behavioral Health Center, Sioux Falls, SD, USA

2 University of Vermont, College of Medicine, Burlington, VT, USA

3 South Dakota State University, College of Pharmacy, Brookings, SD, USA

4 University of South Dakota, Sanford School of Medicine, Department of Psychiatry, Sioux Falls, SD, USA

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BMC Research Notes 2008, 1:133  doi:10.1186/1756-0500-1-133

Published: 22 December 2008



We sought to describe the integrity of human genomic DNA extracted from saliva saturated cotton spit wads stored at -20°C for approximately 11 years. 783 spit wad samples were collected from an ADHD sample population (Vermont Family Study) during 1996–2000. Human genomic DNA was extracted from the spit wads using a commercially available kit; QIAamp DNA Blood Midi Kit (Qiagen, Inc., Valencia, CA.) with a few modifications.


The resulting DNA yield was more than adequate for genetic analysis and ranged from approximately 1 μg to a total of 80 μg (mean 17.3 μgs ± 11.9 μgs). A260/A280 ratios for the human genomic DNA extracted from the spit wads was consistently within the generally acceptable values of 1.7–2.0, with the lowest purity being 1.70, and a mean value of 1.937 ± 0.226 for the 783 samples. The DNA also was suitable for PCR reactions as evidenced by the amplification of the serotonin-transporter-linked polymorphic region, 5HTTLPR. 5HTTLPR is a functional polymorphism in the promoter region of the serotonin transporter gene (HTT, SLC6A4, or SERT), consisting of two intensively studied alleles. 770 of the 783 samples (98.3%) produced fragments after PCR of the expected size with primers specific for 5HTTLPR.


High quality and abundant genomic DNA can be successfully retrieved from saliva saturated cotton spit wads using the commercially available kit, QIAamp DNA Blood Midi Kit from Qiagen, Inc. Furthermore, the DNA can be extracted in less than 3 hours and multiple samples can be processed simultaneously thus reducing processing time.