Furthermore, DNA and DNA banding patterns were obtained from samples containing mixed saliva or semen stains. The DNA banding patterns obtained from saliva or saliva-stained material were impossible to differentiate from the patterns obtained from blood or hair from the same person. DNA banding patterns were obtained from saliva stored at 20 degrees from the isolated DNA and also from dried saliva stains stored under different conditions. This lead to the conclusion that saliva and saliva-stained material can be good sources of DNA for analysis and for DNA typing in certain forensic settings.
Interestingly it was found in a study supported by the National Institute of Dental Research, that when we lick an envelope, we may be sending a more detailed information than we realize. Our saliva leaves a DNA fingerprint that not only says who we are, but also tells that whether we have any genetic tendency for certain diseases. This makes saliva a promising alternative to blood as a source of DNA for genetic testing,
It was found out by Drs. Rob van Scheme and Mark Wilson at the State University of New York that even minor differences such as difference in bases or detect person-to-person differences of as little as a single nucleotide, or structural unit, in the genes. This seemingly small difference in gene structure is known to affect the proper functioning of the immune system.
Diseases potentially connected to these genes include childhood respiratory infections, lupus and juvenile periodontal disease (LJP), a particularly aggressive form of gum disease that occurs in young adults.
As the saliva was believed to have genes that can be screened for genetic diseases, young children can be tested earlier for susceptibility to LJP.
Saliva has other apparent advantages over blood as a clinical tool; being a substitute for blood it opens doors to wide range of population which were not easily accessible. Drawing blood is very invasive and it is not a practical procedure for children or individuals that can't give blood for religious or medical reasons. It is also a frightening prospect for most adults. Provided they can be easily collected, stored and shipped which can be obtained at low cost in sufficient quantities for analysis. They are easy to purify than blood samples.
Forensic scientists can retrieve enough saliva from a postage stamp to identify the person that licked the stamp. Saliva has also been used to test for fragile X syndrome, a rare genetic disorder that causes mental retardation in children who carry the gene.
The technology that allows tiny amounts of salivary DNA to be examined in such detail is a procedure called polymerase chain reaction, or PCR. PCR can be used to replicate small pieces of DNA a billion fold, and with such accuracy minor differences in gene structure are readily distinguishable in laboratory tests. The method is so sensitive one milliliter of saliva (approximately 1/5 teaspoon) yields enough DNA to do over one hundred separate tests. PCR has also been used to identify very small amounts of DNA obtained from fossilized animals, forensic specimens and infectious microorganisms.
Although saliva has the potential to reveal variations in any gene whose sequence is known, but this not proved to b an universal application. Investigators caution that as DNA in saliva comes from many sources, including blood, tissue cells and non-human DNA from bacteria and food particles. Each human gene will have to be validated for accurate PCR identification -- and the number of disease-related genes that have been identified is rapidly growing.
Recently it was proved that adults have a genetic marker for periodontal (gum) disease and hence can be screened with saliva at earlier stage. . Other important possibilities would be the genes for Alzheimer's disease, cystic fibrosis or breast cancer. As the structure of more genes becomes known, it may be possible to test for many genetic disorders from a single sample of saliva.