MISDIAGNOSIS OF HOMOZYGOUS ALPHA-THALASSEMIA-1 MAY OCCUR IF POLYMERASE CHAIN-REACTION ALONE IS USED IN PRENATAL-DIAGNOSIS

The polymerase chain reaction (PCR) is a quite sensitive diagnostic to ol but its specificity may be hampered because of contamination of for eign DNA. In order to determine the diagnostic accuracy of PCR in dise ases due to gross gene deletion, a total of 180 fetuses at risk of hom ozygous South-East Asian deletion (SEA) of alpha-globin genes were inc luded for study. Both PCR and Southern hybridization (SH) were perform ed. By PCR, three of 43 affected fetuses were misdiagnosed as heterozy gotes; four of 50 normal fetuses were misdiagnosed as heterozygotes; a nd four of 87 heterozygotes were misdiagnosed, two as normal and two a s affected. Misdiagnosis in affected and normal fetuses was most likel y due to maternal DNA contamination, while misdiagnosis in heterozygot es was probably due to a failed PCR. In the experiments with PCR in wh ich we added DNA from a carrier woman to an affected or a normal fetus , a level of 1/64 and 1/16 contamination resulted in the appearance of normal and SEA breakpoint sequences, respectively. In the SH experime nts using artificially contaminated DNA, a level of 1/4 contamination showed the normal and SEA bands, respectively, while a contamination l evel lower than lis and 1/16 respectively did not reveal contamination bands. The high sensitivity of PCR makes it easier to amplify contami nated DNA. For accurate prenatal diagnosis, PCR should be performed ve ry carefully and SH seems to be a useful back-up. (C) 1997 by John Wil ey & Sons, Ltd.