In 2006, Lydia Fairchild applied for assistance to help her support herself and her children from the state of Washington. As part of the application, she and her family were tested, in order to prove that they were all related.
Shortly afterwards, the Department of Social Services called her into the office to discuss her case, with a completely unexpected problem: they had determined that the children she had given birth to and subsequently raised were not related to her. According to their tests, the children were not biologically hers.
"As I sat down, they came up and shut the door, and they just went back and just started drilling me with questions like, 'Who are you?'" Fairchild told ABC News at the time. As far as Social Services were concerned, the matter was final.
"Nope," they told her when she tried to question whether there had been a mistake. "DNA is 100 percent foolproof and it doesn't lie."
What was stranger still, was that her boyfriend – the father of the children – was confirmed to be related to them. It was only Fairchild, who remembers giving birth to them, who was not related to her own children. As well as this disqualifying her from receiving financial assistance, she was now suspected of welfare fraud and was at risk of having her children taken away.
Though DNA tests are not foolproof (labs make mistakes, samples get contaminated) in this case, it was correct. A second test came back with the same, strange result. And another. And another. It began to look pretty bleak for Lydia, as the state filed a lawsuit against her for fraud.
But, her case was not unique.
In 2002, 52-year-old Karen Keegan suffered renal failure and needed a kidney transplant. When she turned to her family, she too found out that two of the three children she had given birth to and raised were her husband's biological children, but not hers. Investigation into the cause of this would eventually help Lydia win her case against the government.
Samples were taken from all over Keegan, who they suspected of having tetragametic chimerism. Tetragametic chimerism occurs when two separate eggs are fertilized by two different sperms, and then one of the embryos absorbs the other during the early stages of development. People with this type of chimerism may have two blood types, different eye colors, or other physical signs such as birthmarks down their center.
Chimerism is rare, with only around 100 documented cases in humans. People with the condition can live with no complications from it, other than altered pigmentation. Several people have only become aware of their condition after blood tests.
In chimeric patients, the majority of cells usually end up coming from one set of DNA, Live Science reports. In some cases, the person can develop ambiguous genitalia, if the twin embryos they are developed from contain different chromosomes (ie if one twin is male and the other is female).
None of these signs were present in either Keegan or Fairchild, but after samples from all over Keegan were taken, tetragametic chimerism was found to be the cause. In Keegan's case, the team studying her were able to discover groups of genes linking her children to her own parents.
"Because of the apparent rarity of tetragametic chimerism and the importance of the use of molecular techniques to confirm its presence, this condition may be underdiagnosed," the team wrote in their study.
"Furthermore, if a single cell line predominates in the blood, the chimeric state may not be detected unless family studies are undertaken. Even then, the findings may be misinterpreted as ruling out maternity or paternity."
With this knowledge, Fairchild was able to temporarily fight off claims that she was not her children's mother, while she sought further testing. Sure enough, a cervical swab eventually proved that she had two distinct sets of DNA: she was a chimera. Something she probably would never have known without her unusual legal problems.