Breakthrough in Foetal Down's Syndrome Testing

(From left) Prof. Rossa Chiu Wai Kwun of the Department of Chemical Pathology, Prof. Tze Kin Lau of the Department of Obstetrics and Gynaecology, Prof. Dennis Lo Yuk-ming, Director of the Li Ka Shing Institute of Health Sciences, and Dr. Nancy Tsui Bo Yin, postdoctoral fellow of the Department of Chemical Pathology

A revolutionary approach for the noninvasive prenatal testing of Down's syndrome developed by a team led by Prof. Dennis Lo Yuk-ming from the Li Ka Shing Institute of Health Sciences of the Faculty of Medicine was reported in the latest issue of the top biomedical journal Nature Medicine. This research was supported by the Innovation and Technology Fund of the Hong Kong SAR Government and the Chair Professorship Scheme of the Li Ka Shing Foundation.

In 1997, Prof. Lo and his research team discovered for the first time in the world the presence of foetal DNA in the blood plasma of pregnant women. This discovery has opened up new possibilities of noninvasive prenatal diagnosis. However, the use of this approach for Down's syndrome testing has presented a major challenge to many international groups currently working in this field.

Prof. Lo's team has now managed to achieve this previously elusive goal by detecting RNA molecules which are copied from a gene located on chromosome 21. Using a novel approach based on the measurement of the ratio of such RNA molecules copied from gene copies which the foetus has inherited from the father and mother, Prof. Lo and his team have achieved the noninvasive prenatal detection of Down's syndrome. In cases which can be analysed by this method, the sensitivity and specificity of the test are 90% and 96.5%, respectively. These figures represent the highest yet reported for a single test. While the current, still experimental test can only be used for a proportion of tested cases, this would theoretically half the number of invasive tests needed for Down's syndrome testing. It is anticipated that with further refinement, this test will be ready for routine utilization in the next few years.

The novel Down's syndrome testing strategy developed by CUHK has the following advantages:

• Direct noninvasive detection of fetal Down's syndrome from a mother's blood sample

• As a stand-alone test, can already achieve similar diagnostic accuracy as the conventional strategy that employs multiple testing components

• Can potentially save some normal pregnancies from the need for invasive genetic testing

• Unlike the testing of blood hormones, the test profile does not change with the progression of pregnancy. Therefore, a woman can be tested during any time of her pregnancy.

• Results can be released in a much shorter time-frame than conventional genetic testing, especially those which are based on fetal cell culture.