Tech breakthrough brings two new prenatal tests

The 2018 Policy Address announced the government-backed Hong Kong Genome Project, with the collaboration of HA, Department of Health, universities, private hospitals, and the research and development sector. Simultaneously, HA has introduced two new tests of prenatal diagnosis, namely chromosomal microarray (CMA) in June 2019 and non-invasive prenatal testing (NIPT) soon, expected to handle 1,600 cases and 3,000 cases a year respectively. The tests can detect foetus’ genetic abnormalities in a more accurate, safer and faster fashion.

NIPT: More precise and safer screening for trisomy

Three chromosomal disorders, also known as trisomy, occur when there is an extra chromosome. Trisomy can be detected in Down syndrome (caused by an extra chromosome 21), Edwards syndrome (caused by an extra chromosome 18) and Patau syndrome (caused by an extra chromosome 13). A 6-person team in Hong Kong Children’s Hospital (HKCH), comprising a pathologist, a scientific officer, a bioinformatician and three medical technologists, is responsible for the new NIPT service in HA. Dr Liz Yuen, Consultant (Genetic and Genomic) from HKCH Department of Pathology, explains that NIPT test is 99% accurate and has a false-positive rate of less than 1%. Non-invasive procedure not only reduces the risk of miscarriage due to chorionic villus sampling or amniocentesis, but also avoids unnecessary physical and psychological stress of parents.

Dr Yuen elaborates, “In HA, NIPT is the second-tier screening for pregnant women whose foetus is screened high risk in the first-tier screening performed by any one of our eight obstetric clinics. After receiving the mother’s blood sample from obstetric clinic, the team will test maternal plasma foetal DNA using next-generation sequencing technology. Report will be available within 10 working days and passed to respective clinic for follow-up, which may then consider the possibility of having a chorionic villus sampling procedure or amniocentesis.”

With NIPT service commencing in late 2019, the team is actively preparing for patent application, purchase of equipment, and communication with HA Head Office, hospitals’ Department of Obstetrics, and also IT departments on service details.

CMA: Comprehensive DNA test for congenital abnormalities

CMA testing will be performed for pregnant women under several circumstances, namely when the foetus shows abnormal ultrasound findings; when Down syndrome screening test indicates high risk; or when there is family history of genetic disorder. Genetic samples will be obtained through chorionic villus sampling or amniocentesis.

CMA detects clinically significant chromosomal microdeletions or microduplications, leading to genetic disorders such as Di-George syndrome, Prader-Willi syndrome, Angelman syndrome and Williams-Beuren syndrome. Dr Leung Wing-cheong points out that CMA is more sensitive than traditional karyotyping as it can detect chromosome gain and loss which cannot be seen under microscope. As a result, more than 150 congenital abnormalities can be diagnosed. Some congenital diseases hamper human development in various aspects. “Early diagnosis, appropriate treatment and follow-up ensure better care for pregnant women, better prepare foetus for optimal disease management, or even minimise the risk of developmental delay of the baby,” he says.

After chorionic villus sampling or amniocentesis, the test report will be analysed and prepared by two university laboratories and government clinical genetic service specialists and will be ready in seven to ten working days. Attending doctor will explain the result to the mother and family, but when findings are abnormal or unclear, they will be referred to a clinical geneticist for further counselling. Interpretation of results and counselling support are now available at Tsan Yuk Hospital, Genetic Counselling Clinic under Department of Health, and the medical schools of the University of Hong Kong and The Chinese University of Hong Kong.