Prenatal diagnosis of β-thalassemia

Abstract

This paper reviews the techniques presently available for the prenatal diagnosis of β-thalassemia. At the present time β-thalassemia mutations are detected directly in trophoblast DNA, enzymatically amplified by polymerase chain reaction. Known mutations may be defined by restriction endonuclease digestion, allele specific oligonucleotide probes or allele specific oligonucleotide primers. Unknown mutations are detected by denaturing gradient gel electrophoresis followed by direct sequencing. Other potentially useful methods for unknown mutations are single strand conformation polymorphism analysis and chemical mismatch cleavage anlaysis. A potential pitfall for all procedures based on analysis of amplified DNA is the co-amplification of maternal sequences. This may be avoided by a careful dissection of maternal decidua from fetal trophoblast, by using a minimum amount (5-10 mg) of chorionic villi and by reducing the number of amplified cycles to approximately 20. Monitoring the presence of co-amplified maternal sequences by the analysis of polymorphic sequences is strongly recommended. Future perspective consist of preimplantation diagnosis by biopsy of the morula or blastula or ova genotyping by analysis of the second polar body.