Tetragametic Chimerism Identified During Routine Paternity Testing

Abstract

Introduction: Human chimerism is the presence of two (2) or more cell populations in an individual that contain genetic material from more than one zygote. Phenotypes can range from phenotypically normal men, disorders of sexual differentiation, or phenotypically normal women. We present a case of tetragametic chimerism identified during routine paternity testing in a phenotypically normal woman.

Materials and Methods: With a court order and prior informed consent, a paternity study was conducted using analysis of STR (Short Tandem Repeat) markers Powerplex 16, Powerplex 21, Y-chromosome STR haplotypes, DNA mitochondrial analysis by Sanger sequencing on a 3500 genetic analyzer, and cytogenetic studies. Additional samples from the mother's different tissues, three siblings of the mother, and two additional children from the same mother were analyzed.

Results: The initial STR analysis showed an XY profile in amelogenin in the mother's sample, along with two possible maternal exclusions at the lowest threshold. Further studies on different tissues from the mother (hair, oral mucosa cells, saliva, and blood) demonstrated the existence of tetragametic chimerism, confirmed by cytogenetic studies 46,XY[87]/46,XX[13]. Family studies allowed the reconstruction of parental profiles, confirming the discovery of tetragametic chimerism. Discussion: The frequency of tetragametic chimerism is unknown. Legal implications can lead to various situations with significant economic and criminal ramifications, including loss of financial support in child support, divorce, loss of trust between partners, procedural fraud, immigration denial, and economic claims against forensic laboratories, among others.