Two different genetic profiles from a bloodstain: which one is true?

Contamination, degradation or unsuitable storage conditions of biological samples may produce partial genetic profiles and amplification artifacts of difficult interpretation. Allele drop-out is one of the most frequent stochastic artifacts involving degraded DNA. We report a case where a woman tested positive for alcohol tests performed on blood samples taken following the police custody, had doubts about the origin of the biological sample (blood) analyzed. After a few weeks she has required the comparison of its genetic profile obtained from a saliva sample with that obtained from the blood sample that had been preserved. A stain of blood sample was placed on paper and was divided into four parts, one of these was immediately analyzed, providing a genetic profile that was not compatible with the genetic profile of the woman. Subsequently, another part of the bloodstain was underwent to genetic analysis providing a different genetic profile than the previous stain, but fully compatible with that of the woman. Unexpectedly, two portions of the same trace have produced two different profiles.