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DNA fingerprinting in the twilight zone.

It the close of the last decade, Science announced its intention to counteract the symbolization of years by people by naming a "Molecule of the Year." Nor is this irony. Science's editor, Daniel E. Koshland, Jr., asserts that "our present standard of living depends on" science and technology, and that describing personalities" obscures the "fundamental causes of progress.... The challenge to science is to generate new discoveries. The challenge to society is to use those discoveries for the betterment of all." Although taking some of the spotlight off celebrities is constructive, the implicit claim that science is or should be divorced from society cannot be taken seriously, as a brief discussion of some of society's attempted uses of Science's 1989 "Molecule of the Year" illustrates.

The award for 1989 went to "the DNA polymerase molecule and to the technique called polyrnerase chain reaction, PCR...." PCR is a technique for amplifying small quantities of genetic material into "large quantities of accessible, identifiable, and analyzable material" that can be used to help diagnose diseases and detect pathogens. But, as Science explains, one of the most societally important uses of this technology will be in the area of identifying individuals from small DNA samples:

DNA samples in trace materials (semen, blood, hairs) found at the scene of a crime have been compared with DNA samples from crime suspects; both acquittals and convictions have resulted from such comparisons. Missing persons have also been positively identified through PCR-based comparisons. The resolution of paternity cases has been aided by comparing DNA from a child with that of the alleged father.

This description is of interest because fewer than 5 percent of the approximately 1,000 criminal cases and 3,000 paternity cases in the United States in which DNA technology has been used have involved PCR amplification (almost all em lo the less exacting techniques described below); only one of the three major laboratories doing "DNA fingerprinting" uses PCR; and the example is put forward at a time when DNA matching in criminal cases is under intense attack because the scientific protocols for its use have not been well defined by scientists themselves. DNA fingerprinting, then, provides a useful example for exploring the relationship between science and society. DNA Fingerprinting

A suspect may be placed at the scene of the crime in a number of ways. The most common is by an eyewitness. But eyewitnesses are notoriously unreliable, and most prosecutors prefer to have eyewitness testimony supplemented by physical evidence such as fingerprints or footprints. In violent crimes like rape and murder, the perpetrator may leave his sperm or blood behind, or carry away some of the victim's blood on his person. Using ABO blood groups, individuals can be excluded as suspects. Using DNA typing, however, it has been suggested that suspects can be conclusively identified as the source of blood or sperm. This type of identification has been hyped by law enforcement officials as the ultimate law enforcement tool, and its first use to help solve a murder case is graphically chronicled in Joseph Wambaugh's current bestseller, The Blooding. A California Department of Justice official predicts that "in a few years, a crime-scene sample will tell a suspect's race, eye color, hair color and even his build." Others see DNA samples as eventually being fed into a computer that will decode them and produce "an image like the kind our police artists do now."3 So entrenched had the patina of scientific "fact" surrounding DNA fingerprinting become that although the technique has been used in the courtroom since 1986, it was not until 1989 that criminal defense attorneys even attempted to challenge its validity. These initial challenges have been so successful that effective use of the technology may have been set back years.

How the Test Works

The standard method of DNA fingerprinting utilizes the same restriction fragment length polymorphism analysis (RFLP analysis) used in genetic testing and screening. Restriction enzymes recognize and cut specific nucleotide sequences in DNA molecules. Since the nucleotide sequences in the human genome vary widely from person to person, the restriction sites will also vary, and therefore the length and content of the fragments. RFLP analysis rests on the finding that two samples of DNA from the same individual will produce the same DNA fragments, whereas samples from different individuals (other than identical twins) will produce different fragments from the same site. To oversimplify, the method to produce and compare DNA fragments can be divided into eight steps:

(1) DNA is extracted from the biological samples, usually sperm, white blood cells, or hair roots (this, of course, requires a sufficient amount of noncontaminated material).

(2) The DNA is cut into fragments by restriction enzymes. Different enzymes produce fragments of different lengths.

(3) The resulting fragments are placed in lanes on a gel and separate when an electric field is applied across the gel- the shorter fragments move more quickly than the longer fragments, so that they end up arrayed according to length (there is continuing debate regarding the shifting" or stretching of fragments at this point).

(4) Through a method called Southern blotting, the DNA fragments are transferred from the gel to a nylon membrane to which they are permanently bonded. During this process, the double stranded DNA molecules are treated with a chemical that causes them to "unzip" into separate single strands.

(5) A radioactive probe that binds to specific sites on the DNA fragments is used in a process termed hybridization. Single locus probes lock onto areas that occur only once in human DNA; multi-locus probes produce multiple interpretable bands.

(6) In a process known as autoradiography, the membrane is placed under an x-ray film and bands on the film, known as a "DNA print," are produced by radioactively tagged DNA segments.

(7) A comparison is made between the DNA fragments from the crime scene sample and those from the suspect to see if the bands match," as they should if they come from the same person or that person's identical twin. Matching often requires the use of judgment on die pan of the analyst.

(8) If there is a match," the probability of there being a match involving someone other than the suspect is calculated using population models that are still controversial.

Challenges to DNA Fingerprinting

The test under which most jurisdictions decide whether novel scientific evidence can be introduced in court proceedings is taken from the 1923 Frye case: just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while courts will go a long way in admitting expert testimony deduced from a well recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs (emphasis added).' Although there are only a handful of reported cases involving DNA fingerprinting, all of them have concluded that the technique passes the Frye test The current concern is how well the nation's commercial laboratories are performing DNA fingerprinting. The best known challenge occurred in mid-1989 in New York, in the most comprehensive and extensive legal examination of DNA forensic identification tests held to date in the United States. The pretrial hearing involved an individual accused of second-degree murder in the stabbing deaths of a twentyyear-old pregnant woman and her two-year-old daughter. The prosecution sought to introduce evidence that a blood stain on the defendant's watch matched that of the adult victim. A twelve-week hearing on the evidence produced a 5,000-page transcript and involved ten expert witnesses, five on each side. The DNA analysis had been done by a New York firm, Lifecodes, Inc.

Judge Gerald Sheindlin concluded that it is scientifically possible to do reliable DNA fingerprinting. Having reviewed the stages of DNA analysis described above, however, he concluded that the procedures followed by the testing laboratory involved were woefully lacking. In his words:

In a piercing attack upon each molecule of evidence presented, the defense [New York attorneys Peter J. Neufeld and Barry C. Scheck] was successful in demonstrating to this court that the testing laboratory failed in its responsibility to perform the accepted scientific techniques and experiments in several major respects.

The court faulted the laboratory for using "unscientific and unacceptable" methods and unsound population methodologies. On the basis of the autoradiographs presented in court, he concluded that the DNA evidence could not unambiguously prove that the blood was from the victim. Judge Sheindlin suggested guidelines for future pretrial hearing procedures involving DNA analysis in which the proponent would have to provide the other side with documents regarding twelve elements, including copies of the autorads themselves and the opportunity to examine the originals, copies of laboratory books, copies of quality control tests run, the method used to declare a match, and the data pool and rules used to determine the frequency of the fragment in the population.

This case prompted the National Academy of Sciences to appoint a committee to issue guidelines concerning DNA fingerprinting. The NAS report is expected in early 1991. In the meantime, questions are multiplying.

The most recent setback for DNA fingerprinting as an identifier (rather than an excluder) came in a Maine case that involved a five-year-old girl who had been sexually assaulted behind a school building. The police identified a prime suspect; he matched the description given by the girl and two friends, admitted being in the area at the time, and had tissues in his pockets similar to one left at the crime scene that had been used to wipe semen from the girl's leg. The semen-stained tissue and the suspect's blood sample were sent to lifecodes, Inc. for analysis. The samples did not match, exonerating the individual. A second suspect was apprehended and blood drawn from him. This time lifecodes reported a match.

At a pretrial hearing in early December 1989 on the admissibility of the DNA evidence die defense attorney exposed a problem that Lifecodes had with "bandshifting" as well as some irregularities in the way in which the data was handled. Lifecodes reported that four different probes produced bands from the defendant's DNA that were identical to those in the semen sample from the tissue. The problem, however, was that the bands did not line up, that is, the pattern was the same, but it was displaced in one direction. The company's explanation was that the semen DNA fragments ran faster along the gel than the defendant's. An expert from lifecodes testified that the finn used a single monomorphic probe, that is, a marker for a DNA fragment that is the same in all people, to calculate the correction factor that should be used in comparing the samples. At the 3.15 percent correction given by this probe they matched. Unfortunately for the prosecution, the defense attorney had an internal document from lifecodes (apparently sent to him instead of the prosecutor by mistake) that showed that Lifecodes had used a second monomorphic probe as well, and that this probe showed a bandshift of 1.72 percent. If this measurement were used, there would be no match. When confronted with this evidence the Lifecodes expert reversed his testimony. The prosecutor thereafter withdrew his request to use the DNA evidence (his own independent scientific expert refused to support the methodology used by lifecodes to explain the bandshifting). The prosecutor later wrote Lifecodes to complain that he should have been informed of the problem (of course, both sides should have been so informed), saying "One would have thought ... that after ... People v. Castro, Lifecodes would have taken to heart the lessons learned there." He also noted that because of this hearing, "the use of DNA identity testing in criminal trials throughout the country has been further undermined." He seems correct in both respects.

In another case, involving a murder by stabbing, the Minnesota Supreme Court ruled that DNA fingerprinting evidence cannot be admitted unless the testing laboratory complies with appropriate standards and controls, and [makes] available their testing data and results." In the Minnesota case, the nation's other large private testing laboratory, Cellmark, had refused a defense request for specific information regarding its methodology and population data base, saying that these were trade secrets. The court ruled that such information was essential for due process to afford the defendant with "at least an opportunity for independent expert review.""

What Should Be Done?

There seems little doubt that DNA fingerprinting can accurately exclude individuals from being possible suspects of specific crimes, and it should continue to be so used. On the other hand, major problems have been demonstrated with the methods used (which have not been standardized) by the country's two major private testing laboratories, neither of which have published their methodologies in peer-reviewed journals. Prosecutors should accordingly seriously consider a voluntary moratorium on the use of DNA fingerprinting evidence to identify individuals as suspects, at least until the National Academy of Sciences reports on the scientific protocols that should be used to perform and validate DNA fingerprinting. The alternative to such a self-imposed moratorium is that individual defendants will be forced to spend large amounts of money on experts to discredit test results, and that well-financed defendants will likely be successful, while those represented by public defenders will be unable to mount a reasonable defense. Such a moratorium could also provide the FBI with additional time to have its own DNA laboratory testing procedures (which employ a different methodology than any of the private companies) standardized and published.

Ultimately, there should be national standards involving laboratory procedures and restriction enzymes. We also need to address the issue of whether law enforcement agencies should only use public laboratories for testing so that the laboratories cannot hide behind trade secrets" to withhold information from defendants, and are not motivated by potential profits to get a test to the market before it has been subject to objective scientific scrutiny. In this regard, both defense attorneys and the scientific community at large seem to be in agreement. Attorney Peter Neufeld of the Castro case observes, "It's absurd to think that judges should be the ones to decide when the scientific community hasn't decided yet." Eric Lander of the Whitehead Institute puts it similarly, "The fight place to address these questions [regarding DNA typing] is in scientific journals rather than in courtrooms. This is an extremely powerful technology, but there has got to be a better way to ensure that it is used properly." Scientists must be intimately involved with society if die "Molecule of die Year" is to be useful to our criminal justice system.


1. Daniel E. Koshland, "The Molecule of the Year," Science, 22 December 1989,1541.

2. Ruth Levy Guyer and Daniel E. Koshland, "The Molecule of the Year," Science 22 December 1989,1543-46.

3. Quoted in Jeffrey L Brown, "DNA and KellyFrye: Who Will Survive in California?" Criminal Justice Journal 11 1988),1-87, at 8485.

4. See generally, William C. Thompson & Simon Ford, "DNA Typing: Acceptance and Weight of the New Genetic Identification Tests," Virginia Law Review 75 (1989), 45-108, at 63-87.

5. United States v. Frye, 293 E 1013 (D.C. Cir. 1923).

6. People v. Castro, 545 N.Y.S. 2d 985, 996 (Sup. 1989).

7. See Colin Norman, "Maine Case Deals Blow to DNA Fingerprinting," Science, 22 December 1989, 1156-58; and Alun Anderson, DNA Fingerprinting on Trial," Nature, 21 28 December 1989, 844.

8 State v. Schwartz, 447 N.W 422, 427 (Minn. 1989).

9 Quoted in Rorie Sherman, "DNA Tests Unravel?," National Law Journal, 18 December 1989,1, 24.

10. Quoted in Norman, "Maine Case."
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Title Annotation:use of DNA polymerases to identify criminal suspects
Author:Annas, George J.
Publication:The Hastings Center Report
Date:Mar 1, 1990
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