Sibling incest and formulation of paternity probability: case report

Paternity determination of a fetus whose mother was admitted to an institution for the welfare and health of handicapped persons was requested of us by a doctor and lawyer of the institution. The fetus was recovered by a legal artificial abortion based on the Act on Maternity Health and Welfare (Japan) with the permission of the custodian. Commercially available MCT118, HLADQA, PM, and 9 STRs were tested for DNA samples from the fetus, the mother, her younger brother, her father, her grandfather, and 4 staff members of the institution. Only the brother was not excluded and the paternity probability was estimated at 99.857% on the basis of newly formulated expressions for multiallelic loci on the assumption of sibling incest. We concluded then that the fetus was fathered by the brother. DNA fingerprinting with multilocus and single locus minisatellite probes which were performed to confirm the paternity also support the conclusion. Bandsharing frequencies between the family members, however, did not necessarily reflect their actual kinship, which findings suggest that multilocus DNA fingerprinting requires further accumulation of data for consanguineous cases such as incest. Universal formulation for calculating paternity probability for a sibling incest case on the basis of multiallelic monolocus polymorphisms is also presented.