Molecular evidence of Munchausen syndrome by proxy

Many perpetrators of Munchausen syndrome by proxy present bloodstained materials as counterfeit evidence of proxy hemorrhage. Although blood grouping may show that the blood is not the proxy's, DNA typing may specifically identify the blood's source. A mother claimed that she alone had witnessed gastrointestinal bleeding of her son and presented bloodstained towels as evidence. Several clinical investigations had failed to reveal a bleeding source. I compared the DNA types of the bloodstains and the child's buccal cells. The bloodstain and epithelial cells differed at 4 of 8 microsatellite loci and at the amelogenin locus. The blood and buccal cells shared 1 allele at every locus, suggesting that their sources were closely related. The probability that the source of the blood was maternal was 0.9915 (prior probability, 0.5). I recommend DNA matching in suspected cases of Munchausen syndrome by proxy whenever blood is presented as evidence.