A case of chimerism-induced paternity confusion: what ART practitioners can do to prevent future calamity for families.

In the fertility clinic setting, a negative DNA paternity test result usually suggests a sample mix-up likely occurred at the testing company or in the clinic. However, we report a case where, despite repeat negative paternity test results, the alleged father (referred to as "the proband") was confirmed to be the baby's father. The proband, a 34 year-old male, contacted our research group when routine blood testing revealed discrepant blood types between the parents and the baby, repeat paternity tests were negative (excluding the proband as the baby's father), and the fertility clinic found no evidence of any wrongdoing. Microarray technology was utilized to confirm biological relatedness, which revealed an avuncular (uncle/nephew) relationship. Additional tissue samples were analyzed and family studies were conducted at paternity and forensic laboratories using STR-based DNA tests to elucidate the proband's condition of congenital tetragametic chimerism. His paternity was subsequently affirmed and the fertility clinic exonerated of claims of a semen sample mix-up. This case underscores the possibility that some allegations of fertility clinic missteps may be explained by undiagnosed chimerism, a condition where an individual harbors two distinct genomes. We offer specific suggestions for improving laboratory reporting and creating clinical guidelines to aid in identifying and rectifying future cases of false exclusions of paternity due to chimerism.