Dot blot analysis on enzymatically amplified trophoblast DNA with allele specific oligonucleotide probes is currently used for the prenatal diagnosis of single gene disorders characterised at the molecular level, such as the beta thalassaemias, phenylketonuria, sickle cell anaemia, and alpha 1-anti-trypsin deficiency. A potential problem with the use of this procedure is the co-amplification of maternal sequences, which may obscure the diagnosis in the fetus. To address this question, we carried out prenatal diagnosis of beta thalassaemia in 300 couples at risk by dot blot analysis on enzymatically amplified DNA with 32P or horseradish peroxidase labelled allele specific oligonucleotide probes. We verified the diagnosis obtained by this procedure with oligonucleotide hybridisation on electrophoretically separated non-amplified trophoblast DNA fragments. We detected no co-amplified maternal sequences, even with a faint signal, in the dot blot of trophoblast DNA from those fetuses diagnosed as normal or homozygotes, nor in those diagnosed as heterozygotes, who were born to parents carrying different mutations and had inherited the paternal mutation. These results indicate that, when careful dissection of trophoblast tissue from maternal decidua is carried out, amplification of chorionic villi DNA is not associated with amplification of maternal DNA sequences. We may thus conclude that dot blot analysis of trophoblast DNA is a very reliable procedure for prenatal diagnosis.
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