DNA ‘fingerprints’ to sort out suspects, not catch offenders

Press, 5 March 1988, Page 21

DNA ‘fingerprints’ to sort out suspects, not catch offenders

SARAH SANDS reports:

Forensic samples from 21 suspects in the Teresa Cormack murder inquiry were sent |to Britain recently for tests police believe may identify the killer. The tests will analyse the DNA (deoxyribonucleic acid) of each sample to see if any matches samples taken from where the body of the Napier girl was found.

The test enables scientists to produce a picture of DNA, which shows up on an X-ray as a collection of horizontally stacked bands, similar to a supermarket bar code. Because DNA, which is present in every • human cell, carries a code as individual as a fingerprint, the;sample that matches — if any do — is likely to be that of the killer. The British courts have already accepted the findings of DNA tests as evidence in cases, and in November last year!, a rapist in North Wales was convicted entirely on the result of a DNA testi | : ' The Minister of Police, Peter Tapsell, has strongly indicated that he favours the use! of ‘.‘genetic ■ (DNA) fingerprinting" in fighting crime. However, a Christchurch geneticist using the DNA fingerprinting technique in his research warns that it may be more useful in eliminating suspects than in catching offenders. Dr Francois Iris, of the Christchurch School of Medicine, says the technique has many uses in forensic work, but it also has strict limitations. Testing for DNA “fingerprints” can be done only on cellular material — blood, ■ tissue or semen. Hair and fingernails do not contain cells or DNA and cannot be; tested. The same applies to surface skin because those cells are dead. j This means that in cases, of murder with no sexual aggression. the offender would have to be wounded quite badly, says! Dr Iris. About five millilitres] of blood would be needed for a test,, and police would have to be at' the scene within 24 hours. Any longer than that and the

sample would deteriorate, he says. ! “If the police supply me with an original forensic sample and that sample has been around for a few days, then it will be fairly damaged, and there is no way that I will get a high ] resolution pattern. “I will get a pattern; but there will be so much background that there would be no way I could compare it with another sample and say it was identical. “A sample in bad: condition would mean ! the accuracy would be down at least 20 jto 25 per cent.” |

However, two totally different patterns would be obvious, and this is where DNA testing could help to eliminate suspects, says Dr Iris.

“A sample in poor condition will never give a pattern clear enough to allow the- police to present evidence in court that will lead to a conviction, but it will be good enough to say that those persons can’t !be implicated.”

This could save the police a lot of work by eliminating possible suspects early in the! investigation. . !

The real potential: for DNA testing is in cases of rape and sexual assault, says Dr Iris. Sperm, unlike blood and tissue, has no “self-destruct ’ mechanism that destroys the cell once it is away from the body, he says. “Sperm is a tough envelope with DNA inside it and nothing else — there’s nothing there to destroy the DNA. Tliis means that sperm last a considerable amount of time. We ! can get a DNA picture from sperm that is three months old." | : ■

That clear picture ! should be enough to convict someone, he savs.

: “With a DNA test in the case of rape or sexual assault, we are in a position to say 'you did it and no-one else’ — we can nail a person.” ;

Sperm lias another! advantage

because there is always enough to do the DNA tests ias many times as needed to be! sure the suspect and the guilty person are the same. !

That is not always i the case with blood and tissue.

“For each test, we require five millionths of a gram. |We could push this to an absolute limit of 2.5 millionths of a gram, but we wouldn’t get a full pattern, only the strongest bands, i “If the two suspects were very different there would be no problem, but if they are in! the same pattern it would be very difficult because the strongest bands would be very close.” !

Dr Iris says if the test was to prove a person’s innocence or guilt, several tests would be Speeded.

“I could never pass! a verdict on just one run — three runs, yes, but not bne.” | With each test using some of the limited -supply of forensic samples collected by the police at the scene of the crime, there would be no room fori error, he says.

“Extracting DNA is a very, very lengthy and difficult process. It is a very long!molecule, and the longer it is, the easier it is to break, and we don’t want that to happed'. I

“Exactly how long! it takes depends on how good you are. It normally takes a whole day’s work (to extract one- sample), but if you start with whole cells then; it’s 32 hours. We could do it roughly in two hours, but it would be no good for: what we want to do.”! Dr Iris and three others in the School of Medicine’s! diabetes research laboratory have been using DNA fingerprinting for the last year. They are trying to find out why some people] are susceptible to auto-immune diseases, such as diabetes, while others are protected, j

In order to identify! the gene that causes diabetes, tests must

be done on identical twins, one of whom has the disorder and one who does not.

The twins have to be monozygotic! (from one egg) so the genes are identical. The! DNA test proves that the twins are from one egg because both DNA patterns appear exactly the same, i :

If successful, the research has the potential to make preventive treatment for diabetes possible, says Dr Iris.

“At the moment it is impossible to tell who is going'to get the disorder and who is not. We are trying to find a genetic basis for susceptibility to the disorder because this would make preventive treatment possible. “If we can predict it before it’s there, then we have a chance to stop it!— by the time we know the disorder is there, it’s too l&te.” i i ; Dr Iris says his reason for “going, public” about |the testing being done in Christchurch was his annoyance at the Teresa ..Cormack samples being sent overseas without consultation with the scientific community in New Zealand: i

“They didn’t bother! to find out whether given a bit of time we could ! do it. They; sent the samples out, costing a ! lot of money, with no consultation whatsoever.”

Dr Iris says he realises that testing the Teresa Cormack samples is urgent, but ! he is concerned that the potential for developing the testing technique for the future in New Zealand is not being recognised! "For God’s sake, ] before you send things overseas, look in your own backyard. Scientists work in this country competently like everywhere else.

“The technology for DNA testing is: very, very difficult, and it gave us a lot of trouble, but now we’ve got it going in this! laboratory, there is no reason why we should hog that technology to ourselves." ! !