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New blood test for fetal genetic disease shows promise

8 December 2008
Appeared in BioNews 487

A new method for early detection of genetic diseases in unborn babies using a simple blood test can detect the inherited condition beta-thalassemia, according to a study published in Proceedings of the National Academy of Sciences. Although the technique, which  analyses cell free fetal DNA (cffDNA) present in the mother's blood, has previously been used for detecting Down's syndrome, sex determination in pregnancies at high risk of serious genetic disorders affecting a specific sex, and 'Rhesus testing' to help spot women whose babies have a blood type incompatible with theirs, this is the first time it has been possible to detect a single-gene disorder in the developing fetus.

So-called 'Non-invasive Prenatal Diagnosis' (NIPD) can be carried out much earlier in the pregnancy than conventional method and is considered less risky than techniques such as amniocentesis, which carries up to a 1 per cent risk of miscarriage and chorionic villus sampling (CVS), which carries up to a 2 per cent risk.

The researchers, based at the Chinese University of Hong Kong 'Diseases can be diagnosed by a simple blood test taken from the mother ... and by counting the relative ratio of the mutant genes against the normal genes', said lead researcher Dennis Lo at the Chinese University of Hong Kong, who led the research.

Diseases such as beta-thalassemia, which are caused by a change in a single gene, result when the baby inherits two copies of the altered gene, one from each parent. Until now the detection of so-called 'single-gene disorders' has proved to be challenging, because they involve gene changes which differ only slightly from the mother's genetic code, perhaps by only one or two base pairs.

The new technique uses digital DNA analysis from the blood to count the number of copies of a gene. Calculating the ratio of normal to faulty copies overcomes the difficulty of distinguishing between maternal and fetal copies of the gene involved in beta-thalassemia. The accuracy of the test, however, does depend on the concentration of cffDNA in the mothers blood. Around 5-10 per cent of a pregnant woman's blood plasma comes from the fetus and  contains fetal DNA.

Dr Lo cautioned that although the test works in principle, clinical trials are some years off as the process is still expensive and inefficient.

There are concerns from anti-abortion campaigners that advances in prenatal testing for genetic diseases could lead to a rise in terminations. However, Lyn Chitty, who studies fetal medicine at University College London, said: 'there may be more tests, but people don't just have a test to decide whether to have an abortion, sometimes it's just to prepare themselves'. Dr Lo said: 'This new test saves those babies who would be incidentally aborted by invasive testing through amniocentesis'.

Genetic disease testing advance
BBC News Online |  25 November 2008
Safer fetal test for genetic diseases on horizon
New Scientist |  25 November 2008
Simple no-risk prenatal blood test may detect vast range of genetic disorders
Scientific American |  25 November 2008
23 June 2014 - by Dr Anna Cauldwell 
Two patients with the serious inherited blood disorder beta-thalassemia have been able to stop blood transfusions 12 days after receiving experimental gene therapy...
4 November 2013 - by María Victoria Rivas Llanos 
A new method for prenatal testing for Down's syndrome will be tried out at Great Ormond Street Hospital for Children (GOSH), London....
14 January 2013 - by Dr Daniel Grimes 
US biotech company Verinata Health has reported sequencing fetal DNA taken from pregnant women's blood to test for genetic abnormalities...
10 December 2012 - by Dr Lux Fatimathas 
More sensitive prenatal testing of fetal DNA could improve the detection of genetic diseases, studies find...
26 November 2012 - by Dr Lux Fatimathas 
Non-invasive pre-natal screening for certain abnormalities in fetal chromosomes should be offered to at-risks mothers, recommends the American College of Obstetricians and Gynecologists...
12 September 2011 - by Professor Vardit Ravitsky 
An up-and-coming technology will soon allow genetic testing of a fetus with a simple maternal blood test early in the first trimester of the pregnancy by isolating cell-free fetal DNA in the mother's plasma. Currently, obtaining reliable diagnostic genetic information requires invasive testing with Chorionic Villus Sampling (CVS) or amniocentesis. Both carry a risk of miscarriage and are performed between weeks 10 and 20 of the pregnancy...
15 August 2011 - by Rose Palmer 
A simple blood test for pregnant women can accurately predict the sex of a fetus at seven weeks, much earlier than conventional techniques, new research has found. A systematic review and meta-analysis examined the results of 57 earlier studies that included more than 6,500 pregnancies...
13 December 2010 - by Julianna Photopoulos 
Scientists have scanned the entire DNA of an unborn child from the mother's blood sample for the first time to safely check for genetic disorders...
16 February 2009 - by Dr Philippa Brice 
Cell-free fetal nucleic acids - DNA or the related molecule RNA - are present in the blood. As has previously been reviewed, the discovery that a small proportion of the cell-free nucleic acids in the mother's blood during pregnancy actually comes from the fetus paved the way for new techniques to exploit...
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