18 May 2005
Definitive prenatal diagnosis of many genetic and chromosomal disorders currently requires fetal cell sampling by amniocentesis or chorionic villus sampling, invasive procedures with an associated risk of miscarriage of about 1%. As the number of disorders for which prenatal screening and diagnosis is offered increases, interest in alternative non-invasive means of obtaining fetal cell samples has grown. Fetal DNA is present in small quantities (around 3-6% of total DNA) in maternal plasma, and the potential for diagnostic approaches using maternal blood samples is an area of particular interest. The major difficulty is in accurately discriminating fetal from maternal DNA; the specificity and sensitivity of analysis for fetal markers is a key factor in determining the reliability of such approaches. A technique called real-time quantitative PCR (polymerase chain reaction) has proved valuable for allowing amplification of fetal-specific DNA sequences. However, for many genetic diseases the genetic differences between maternal and fetal sequences are very subtle.
A paper published in Proceedings of the National Academy of Sciences of the USA (PNAS) this month reports on a novel method for prenatal diagnosis of