November 25, 2008

Blood Test May Soon Warn Of Inherited Diseases In Fetuses

Researchers claim blood samples taken from expectant mothers may soon reveal if her baby has a wide range of genetic diseases such as cystic fibrosis, thalassaemia and sickle cell anemia.

In the past, prenatal diagnoses of such disorders have been possible only through invasive procedures like amniocentesis "” the extraction of a small amount of fluid from the sac surrounding a developing fetus. Such a procedure carries a greater risk of fetal miscarriage.

Now, a Chinese University of Hong Kong team may have found a way to diagnose in fetuses such "monogenic" diseases, which are caused by a single error in a single gene in the human DNA.

People have two copies of every gene, one from their father and one from their mother. When they conceive a child they pass on one of these gene copies.

However, couples trying for a baby may be oblivious to a hidden disease threat posed by "recessive" genetic disorders.

Lead researcher Dennis Lo at the Chinese University of Hong Kong, said those types of diseases can be diagnosed by a simple blood test taken from the mother that counts the relative ratio of the mutant genes against the normal genes.

Lo and his colleagues said it is only possible because fetal DNA circulates in maternal blood, a discovery made several years ago.

Since that time, scientists have been trying, with little success, to find the best way to differentiate fetal DNA from maternal DNA before they can even get down to looking for any anomalies in the fetal DNA.

Lo and his team said they have devised a counting system that could bring non-invasive prenatal diagnosis of monogenic diseases closer to reality.

The researchers used highly precise digital blood testing technology to count both mutant and normal DNA sequences in maternal plasma. They then calculated the number of mutant genes inherited by the fetus to determine the probability of the fetus developing any monogenic disease.

The accuracy of this method, however, would depend on the concentration of fetal DNA in maternal blood, Lo acknowledged.

Thalassaemia is a blood related genetic disease that can result in reduced fertility or even infertility. Early treatment can improve the quality of life of patients.

Cystic fibrosis affects the respiratory, digestive and reproductive systems and can lead to fatal lung infections.

"We are very interested to hear about this new research, which in principle should make it easier and less risky to test a fetus for cystic fibrosis," said a spokesman for the Cystic Fibrosis Trust.