As DNA tests have become much more sophisticated and more widely used to treat more diseases, doctors have stumbled onto a conundrum: while seeking to diagnose genetic disorders, there's a chance they may discover cases of incest. Long chains of identical DNA are a sign that the patient's parents were father-daughter, mother-son, or brother-sister. The dilemma for doctors who see such results is that they may be legally obligated to violate doctor-patient confidentiality and alert the police.

About half of kids born to parents who are first-degree relatives have a developmental disability, The Houston Chronicle's Todd Ackerman reports. Since the Baylor College of Medicine began using the new test six months ago, doctors have noticed a few--but less than 10--potential incest cases, according to Arthur Beaudet, a geneticist there. Beaudet wrote a letter to The Lancet about the bioethical questions raised by the testing. (, which is being used in a couple dozen of the biggest medical centers in the U.S. )

If the parent of the patient is underage, doctors have to report suspected child abuse. But if the parents are consenting adults, a doctor's obligations are murkier. Beaudet says doctors now have evidence for something they long suspected but couldn't prove was happening--instances of incest are often hidden by families--and medical institutions should take advantage of the new technology "to open people's eyes to what goes on and discourage the problem."