Abstract
M.Tech. (Biomedical Technology)
Despite the introduction of prophylactic treatment for Rh negative females, Rhesus
Haemolytic Disease of the Foetus and Newborn (HDN) remains a problem. The serological diagnosis of this disease is mainly by maternal antibody identification and titration and the estimation of the optical density deviation (ODD) at 450 nanometers of the amniotic fluid. The correlation of these two results is not always good. The advent of molecular biology techniques such as the Polymerase Chain Reaction (PCR)
and the sequencing of genes heralded the start of prenatal diagnosis of genetically inherited diseases and also enabled the prediction of the Rhesus group of the foetus.
It would be advantageous to be able to predict with certainty the RhD status of a foetus
suspected of having HDN without subjecting the mother and foetus to the risk of multiple invasive procedures such as Chorionic Villus Sampling (CVS) and Foetal Blood Sampling(FBS). The amniocentesis performed initially on a mother suspected of carrying an affected foetus would provide the sample necessary for the extraction of foetal DNA for prenatal Rh determination. Two PCR assays were used to determine the RhD group of the foetus: one using two primers amplifying a section ofIntron 4 and the other using four primers, two specific for Exon 7 and two specific for Exon 10 of the Rh gene. In 85.7% (18/21 cases) there was complete correlation between the molecular and the serological methods for RhD determination. One White foetus presented a unique profile, that of RhD negative in both molecular assays and
RhD positive serologically. In the non-White group there were discrepancies between the two molecular methods as well as between the molecular and the serological methods used. This study shows that great care should be taken in the interpretation of RhD status prenatally using molecular biology techniques especially in the non-Caucasian population of South Africa in which there are many polymorphisrns in the Rhesus blood group system. For the moment, the results should be used in conjunction with serological results and clinical parameters for the diagnosis and treatment of Rh HDN.