A SINGLE cell was all it took. After 13 years of separation caused by war, a young Salvadoran boy was recently reunited with his mother - the result of a speck of blood examined under a microscope by scientists a world away, in Chicago.
The emotional reunion underscores the growing use of DNA as a tool to find missing children by human rights organizations and other groups.
Harnessing the same technology used by investigators in the O.J. Simpson murder case, forensic scientists are now comparing the genetic makeups of children - sometimes missing since infancy - with the genes of their parents or relatives.
``We're beginning to apply this now,'' says Clyde Snow, a forensic anthropology consultant in Norman, Okla. ``It's got tremendous potential - not only in human rights cases in other parts of the world, but also in this country.''
Though seldom used in the United States, gene-matching programs have become familiar in Argentina and El Salvador and could be put to use soon in Rwanda. Anywhere a war or disaster separates parents from children - such as in the case of 13-year-old Nelson Ramos in El Salvador - DNA can be utilized to reunite them, says Eric Stover, head of Physicians for Human Rights (PHR), a Boston-based group active in using DNA to find children worldwide since 1986.
Some, though, are concerned that science is getting out in front of ethics. ``These techniques have the power to identify individuals years after they've been lost - when they've already grown up as someone else's child,'' says Eric Juengst, a biomedical ethicist at Case Western Reserve University in Cleveland. ``And then what do you do? Do you reunite them with their biological parents on the basis of genetic information alone?''
WHAT about the other aspects of parenting and family, Dr. Juengst asks.
DNA (deoxyribonucleic acid) is an organic substance, found in almost all cells, that determines a person's genetic makeup. Each individual (except identical twins) has a unique DNA pattern.
DNA as a tool for identifying missing children was first employed in 1984 in Argentina. Human rights groups teamed up to find those who had ``disappeared'' during the country's brutal military dictatorship, which lasted from 1976 to 1983.
``The real impetus came from the families themselves,'' Mr. Stover says, referring to the DNA work begun by a team of US scientists and continued today by Argentines. ``Families of the disappeared will not give up. They are really determined.''
Word of the Argentine program's success spread, prompting DNA use in identifying the dead in Guatemala, Mexico, and Chile, and in finding missing children in El Salvador.
DNA testing produces evidence that is nearly irrefutable and can be used by families in the battle they must sometimes wage against the government to regain custody of their children. This is critical in many third-world countries where other documentation, such as updated dental records, does not exist, Dr. Snow says.
But in the US, DNA-identification techniques mostly have been limited to solving crimes in which the victim is already dead. Mark Stolorow, director of operations at Cellmark Diagnostics in Maryland, the largest private DNA laboratory in the country, says a very small percentage of the cases his company sees involve missing children. Most criminal kidnappings, he surmises, are solved with fingerprints and other more traditional identifying evidence.
DNA use has been highly publicized in criminology and medicine. But other applications are being explored - such as relationship charting among dolphin and whale populations and historical identification, where researchers would, for instance, test blood from John Wilkes Booth to determine if he was President Lincoln's assassin.
The largest DNA identification program in the world now is conducted by the US Army. All new recruits must supply a blood sample that is put on file and can be used to identify the missing-in-action.
Others, meanwhile, are expanding DNA-identification programs. This July, for instance, Robert Kirschner expects to become director of a new international forensic program that Physicians for Human Rights hopes to open in Chicago, funds permitting. At the branch office, PHR will increase its gene fingerprinting, start a DNA data bank, and expand training for foreign physicians and technicians.
``The more of this kind of work we do, the more people recognize its value,'' Dr. Kirschner says. ``It documents human rights abuses in a way that testimony cannot.''