Atypical short tandem repeat allelic patterns in a sexual assault case involving hematopoietic stem cell transplantation

Short tandem repeat (STR) profiling is a cornerstone of forensic DNA analysis, particularly during criminal investigations. However, certain clinical conditions, such as bone marrow transplantation, can complicate interpretation. To illustrate the impact of allogeneic bone marrow transplantation on forensic STR analysis, this case report details a sexual assault investigation involving a female victim who had previously received a bone marrow transplant from a female donor. A female sexual assault victim underwent forensic examination, during which multiple biological swabs were collected. STR profiling was conducted on the victim's blood, fingernail, buccal, breast, hip, vulvar, vaginal, cervical samples, panty, and brassiere. As conflicting profiles were found, a detailed medical history was collected, and hair follicle analysis was performed to confirm the origin of the STR profiles. Blood STR profiling revealed a single female genotype, while multiple swabs, including vaginal and cervical samples, showed a second female STR profile alongside the first. Notably, the consistency and distribution of the mixed profile across samples reduced the likelihood of laboratory contamination. The medical history of the victim revealed a prior history of allogeneic bone marrow transplant. Hair follicle analysis identified the recipient's original genotype, confirming that the secondary STR profile originated from the donor. Bone marrow transplantation may result in a mixed STR profile, potentially leading to misidentification or misinterpretation of forensic evidence. Awareness of transplant history is crucial during forensic evaluations. However, such clinical history is currently not included in standard sexual-assault evidence forms, underscoring the need for procedural updates.