these components are highly variable and are not useful for personal identification. Not listed among the constituents found in urine are the epithelial cells from along the urinary system. Human DNA in urine comes from epithelial cells that line the ureters, bladder and urethra. A small number of cells are sloughed off every day, and with techniques available for DNA typing today, especially polymerase chain reaction (PCR), DNA profiles can be obtained from a very few number of cells. The existence of DNA in excreted
urine is well established and represents a potentially useful source of genetic mate- rial necessary to perform DNA analysis. DNA analysis can be used to uniquely identify the origin of the cells and there- fore the origin of the urine that has been drug tested. The same DNA analysis systems are commonly used for crimi- nal prosecutions and have a matching probability of greater than 1 X 1017th. The reference sample from the indi- vidual contesting the results can easily be obtained using a swab rubbed inside the mouth. The cells from the lining of the cheek will have the identical DNA profile as the cells from the urinary tract from the same person. If the DNA matches the genetic laboratory would conclude that the urine sample and the cheek cells originated from the same source. If they do not match they are not from the same biological source. For DNA testing to be effective there
must be undegraded DNA to test. DNA can be degraded by many conditions such as heat, UV light, high or low pH, bacterial or fungal growth, and DNA degrading enzymes. Urine samples may provide conditions favorable to DNA degredation and therefore should be kept in a manner to protect the integrity of the sample for both drug testing and DNA analysis. Several studies have been conducted to study the stability of DNA in urine samples.
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Cannas et al. measured the stability
of urinary DNA over 28 days, at four commonly examined storage tempera- tures (room temperature, +4C, -20C and -80C), with and without the urine preservative EDTA at two geographically distinct sites.1 Their findings reflect the contradictions in the existing literature, as they observed significant variability in urinary DNA stability irrespective of storage conditions when sampled from different sources. Their results showed that the stability of human DNA in urine can even be dependent on geographic origin (Italian vs Zambian). The varia- tion in stability of human DNA was pre- sumably due to differences in the urinary matrix between locations dictated by the population or other factors affecting the properties of the urine. However, an earlier study by Yasuda et al. could dem- onstrate a positive effect on storage when the preservative sodium azide was added to the sample indicating that bacterial growth may cause a decrease in the isola- tion of DNA for subsequent analysis.2 In this same study if the urine samples were kept at 4C with sodium azide, good DNA could be isolated 100% of the time after at least 5 weeks. DNA Solutions’ DNA testing has been successful with urine samples kept refrigerated for as long as 4 months. Frozen urine specimens collected 15 to 25 years ago were used in one study with a PCR success rate of 89.3%. 3 Isolation of DNA from urine can be highly variable; however, lower temperature storage and the addition of preservative can help preserve the integ- rity of the DNA for genetic analysis. It is interesting to note that two studies
have found that there is a significant dif- ference in the ability to isolate DNA from female and male produced urine.4,5 In each case, less female urine was needed to produce a complete DNA profile than urine from males collected at the same time under the same conditions. Either
an increase in the number of sloughed cells or conditions that favor the stabili- zation of the DNA could account for the better results from female urine. Due to the unstable nature of DNA it
is in the best interest of the tested person to have the DNA analysis completed within the shortest time frame to have the highest probability of obtaining a DNA profile from the stored urine sample. The success of the testing will depend on how long ago the sample was collected, how it has been stored, the composition of the urine and possibly any bacterial load present at the time of collection. Techniques for DNA isolation and genetic identification have continued to improve and will likely lead to a high success rate in future DNA testing from urine samples. ❚
Footnotes
Cannas A, Kalunga G, Green C, Calvo L, Katemangwe P, et al. (2009) Implications of Storing Urinary DNA from Different Populations for Molecular Analyses. PLoS ONE 4(9): e6985. doi:10.1371/journal.pone.0006985
Yasuda T, Iida R, Takeshita H, Ueki M, Nakajima T, KanekoY, Mogi K, Tsukahara T, and Kishi K (2003) A Simple Method of DNA Extraction and STR Typing from Urine Samples Using a Commercially Available DNA/RNA Extraction Kit*.J Forensic Sci., Vol. 48, No1 Paper ID JFS2002184 481
van der Hel O, van der Luijt R, Bueno de Mesquita H, van Noord P, Slothouber B, Roest M, van der Schouw Y, Grobbee D, Pearson P, and Peeters P. (2002) Quality and Quantity of DNA Isolated from Frozen Urine in Population-Based Research, Anal Biochem. May 15;304(2):206-11.
Nakazono T, Kashimura S, Hayashiba Y, Hara K, Matsusue A, and Augustin C. (2008) Dual Examinations for Identification of Urine as Being of Human Origin and for DNA-Typing from Small Stains of Human Urine. J Forensic Sci Vol53, #2. dio:10.1111/ j.1556-4029.2008.00675.x
Nakazono T, Kashimura S, Hayashiba Y, Kenji Hara K, and Miyoshil A. (2005) Successful DNA Typing of Urine Stains Using a DNA Purification Kit Following Dialfiltration. J Forensic Sci, Vol. 50, #4 Paper ID JFS2004484
Brandt G. Cassidy, Ph.D., Laboratory Director, DNA Solutions, 840 Research Parkway, Suite 551, Oklahoma City, OK 73104. Dr. Cassidy has over 25 years of laboratory experience in DNA analysis. His laboratory offers discriminating genetic analysis in humans, animals, and plant species. DNA Solutions is accredited by the American Association of Blood Banks and ISO/ IEC 17025:2005 for human relationship testing.
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