The issue has long lurked in the background of medicine. It's not hard to figure out if your blood type is compatible with Mom's and Dad's(If they are both A positive and you are B positive, you have a problem.)
A recent survey of 56 kidney transplant centers by the University of Maryland showed that 70% had stumbled upon at least one case of non-paternity as a result of testing potential organ donors.
DNA testing has opened the gates of possibility. The potential for surprises exists whenever members of the same family are tested.
For example, researchers looking for the genetic fingerprints of certain diseases have long compared child and parent DNA.
Every so often, mismatches pop up that raise the possibility of hanky-panky.
In research, subjects have signed waivers agreeing that discoveries of non-paternity will not be revealed to them or anybody else.
But in medical practice, the truth has a way of cruelly asserting itself.
In the most common scenario, a child is born with Tay-Sachs disease, cystic fibrosis or another disorder that requires the contribution of a certain gene from each parent. The parents are tested, and the father is found not to carry the gene.
Breaking the news falls to genetic counselors, who often must balance competing ethical imperatives.
"Non-paternity is one of the issues that genetic counselors dread but at some point in their careers will have to deal with," said Andrea Atherton, a counselor at Children's Mercy Hospital in Kansas City, Mo.
Standard practice is to tell only the mother, who usually already suspects it, genetic counselors say.
Ana Morales, a genetic counselor at the University of Miami, recalled the case of a child diagnosed with a type of albinism that can be accompanied by lung and kidney disease.
The mother "told me she was having an affair," Morales said.
"She said she would be in physical danger [if her husband found out]. He had threatened her if she was unfaithful."
Morales did not tell him.
But withholding the information means that the woman's husband lives with the false belief that he is a carrier of a genetic disorder.
That sort of information is far from benign, said Dr. Wayne Grody, a UCLA geneticist. It could convince him to give up on the idea of having children. And in the event that the wife becomes pregnant by her husband, perpetuating the lie could require unnecessary prenatal testing.
