Wednesday, March 9, 2011
Cracking crimes with a new DNA technique
By examining the unique elements that make up a person's DNA, Israeli scientists have made it possible to provide DNA as evidence even when there are multiple sources at a crime scene.
A new invention from Israeli scientists looks deeper into DNA to show with certainty whether or not a suspect was at the scene of a crime.
It's news that will have cold case murder victims smiling in heaven. Israeli scientists have found a way to identify DNA that would otherwise be inadmissible in court - when it comes from a sample of multiple people.
Although forensic DNA analysis is used in less than one percent of all criminal cases, it has helped convict suspects in some of the world's most heinous crimes, including murder and rape.
Providing certainty without a reasonable doubt is not possible when the DNA comes from multiple sources at a crime scene. According to police officials in Israel, this happens in about one in 10 cases, meaning that important evidence for putting a criminal behind bars is lost.
But a new technique developed at the Hebrew University of Jerusalem by a professor and his student takes the uncertainty out of DNA samples, when more than one person's DNA fingerprint is in the mix.
The results were published recently in Forensic Science International: Genetics.
While Prof. Ariel Darvasi from the Department of Genetics doesn't focus on forensics in his day-to-day life, he decided to supervise Lev Voskoboinik's research after hearing Voskoboinik lecture about the problem and declare that there was no solution. Voskoboinik works at the Israel Police Forensic Biology Laboratory and was looking to earn a second degree in DNA analysis.
Solving the unsolvable
"The questions and problems I like best are where people think there are no solutions. I prefer to think about the problems as solvable - that was the starting point," says Darvasi.
"Primarily I am working in research related to human diseases, developing standards and research and have never been much into forensics," he continues. "Forensics though was always a topic I found of interest and there are similarities due to the nature of my research.
"Lev came to my lab with the intent of doing a PhD. I suggested that he do something related to his work."
The two went through Voskoboinik's day on the job, and it was only after listening to Voskoboinik present his work to the lab group that the idea surfaced.
In his lecture, Voskoboinik described one of the cases that are common at a crime scene - when blood from more than one victim gets mixed together. In this case, the crime was a murder by gunshot and there were residual skin cells in the DNA sample mixed in with the blood.
Bioinformatics and computation biology
It can happen in any crime, and in one out of 10 cases, says Darvasi, the evidence becomes inadmissible. Voskoboinik said that nothing can be done about it. But he picked the right supervisor, because it was when he said that, that Darvasi came up with the plan.
"That was a year ago or so," he says. "And we developed a strategy to solve this problem. We proved the concept and theory mathematically. Strategically, we proved that we can identify the DNA with certainty in the presence or absence of certain markers."
While it will take more replications and validation before it can be used in the court of law, Darvasi believes that it's just a matter of time. The invention that relies on looking at rare base pairs in DNA is now being commercialized by the university's tech-transfer arm Yissum and "I have no doubt that it will be used in court," the researcher states.
Expected to cost $100 to $200 per test, the new technology is a combination of bioinformatics and computation biology. The actual strategy was built on the basics of molecular biology using a lab on a chip.
It requires pinpointing the rare and unusual parts of a suspect's DNA, rather than reading the DNA to test a mixture to see if the suspect is present or not.
A new tool for CSIs
Almost every cell in our bodies contains DNA. It is the genetic material that tells our cells how to work. Although 99.9 percent of human DNA is the same in each and every one of us, Darvasi is interested in the very minute parts of the 0.1 percent that are unique.
If all points of the rare DNA are in the suspect and the mixture as well, there is strong proof that the suspect was at the scene. To find the rare points, the team looks at all the rare variants that are spread throughout the entire genome and which are not linked one to the other.
The technique consists of investigating the DNA mixture and the suspect's DNA for 1000-3000 single letter changes (polymorphisms), which are considered relatively rare in any population.
Current DNA fingerprinting methods look at only a few polymorphic sites to see if there is a match. Darvasi's invention looks deeper into the sample to establish with a very high level of certainty whether or not a suspect's DNA is in a mixture of up to 10 people.
Looking at large numbers of base pairs, the team can show beyond a reasonable doubt whether or not the suspect was in the sample. Darvasi predicts that with the right investment, the technology could be developed into a product within a year.