9 May 2005
Prenatal testing for hereditary diseases and genetic abnormalities generally requires the use of amniocentesis or chorionic villus sampling (CVS), invasive procedures with a small but significant associated risk of miscarriage. Recently, there have been moves towards developing non-invasive methods of testing using fetal cells present in the maternal blood or plasma. Analysis of cell-free enriched samples of fetal DNA derived from maternal plasma has already been shown to be effective for the identification of fetal genetic traits that differ from the mother, such as the presence of Y-chromosome specific sequences, or the RhD gene in Rhesus negative mothers. However, this approach is not suitable for the analysis of fetal genetic traits that do not differ largely from the maternal alleles. A paper in the latest edition of the Journal of the American Medical Association reports on the use of a novel technique to detect fetal point mutations associated with the hereditary disorder beta thalassaemia.
The Swiss researchers have previously shown that fetal DNA present in maternal blood samples can be selectively enriched based on their size, which is typically smaller than maternal DNA sequences also present (an average of around 300 base pairs, rather than 500 base pairs for the maternal DNA). They then set out to investigate whether this would permit the detection of fetal point mutations [Li Y et al. (2005) JAMA 293, 843-849]. These most subtle forms of mutation underlie many monogenic disorders, including