Caution on Genetic `Fingerprints'

DNA ``fingerprints'' - supposedly more reliable than real fingerprints for identifying individuals - have been put on trial and found wanting. Ruling on the admissibility of such evidence in a Bronx murder case, New York Judge Gerald Sheindlin has ruled that certain DNA evidence can't be used in the trial because the tests were technically flawed. This ruling, following a 12-week pretrial hearing, confirms what expert witnesses have been saying for months. Supposedly reliable DNA typing isn't necessarily reliable at all.

This should give proponents of the technique pause.

DNA typing depends on the biological fact that two individuals are highly unlikely to have the same DNA patterns (which carry their genetic information) unless they are identical twins. Thus, if DNA from a crime scene matches that of a suspect, this would link the suspect with that scene.

But the subtle comparison is not as straightforward as matching up real fingerprints. Also the likelihood of a match due to chance depends on how many people share a distinctive genetic pattern in the population to which a person belongs. Testers have tended to use statistics for large populations, whereas a suspect (or victim) may belong to a close-knit, perhaps inbred subgroup. This makes the claims of astronomical odds against a DNA match being mere coincidence somewhat dubious.

In the Bronx case, tests showed that blood on the suspect's watch was not his own. Judge Sheindlin ruled those tests admissible as evidence. But he ruled tests purportedly matching the DNA in the blood with the victim's DNA to be flawed and inadmissible. This confirmed the judgment of scientists that the tests did not follow good laboratory procedure.

The ruling doesn't find DNA typing, in itself, inadmissible as legal evidence. It only rules out testing with technical and procedural flaws. But this raises the larger issue of what are proper standards for DNA ``fingerprinting.''

Some eminent molecular biologists say there are not yet generally accepted standards, especially for the interpretation of test results. Eric S. Lander of the Whitehead Institute in Cambridge, Mass., for example, says flatly that ``we, the scientific community, have failed to set rigorous standards ... with the result that some of the conclusions presented to courts are quite unreliable.''

Judges and jurors, who can't be expected to understand the technical details of DNA analysis, tend to accept test findings as unarguable scientific proof when, in fact, they are not. Yet some convictions have turned on DNA evidence.

The congressional Office of Technology Assessment is making a comprehensive study of DNA ``fingerprinting.'' The National Academy of Sciences is expected to commence a study of its own soon. Until these studies are assessed and adequate standards set, the legal community should put DNA ``fingerprinting'' on hold.