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Genetic link to 4,000 diseases

  Thursday, 12 l 05 l 2011  Source: Mind Your Body; The Straits Times   
By: Lee Hui Chieh

Thousands of other genetic tests are being used today – many on pregnant women and newborn babies – to diagnose and manage genetic conditions that can be passed on to the next generation. Scientists have managed to make strong links between genetic defects and about 4,000 heritable diseases, said Associate Professor Denise Goh, who heads the division of paediatric genetics at the National University Hospital’s University Children’s Medical Institute.

They have devised genetic tests that doctors can use to test patients for close to 2,000 single gene defects that cause such diseases, which tend to be very rare, she said. More types of such tests have been created in the last few years and more are being used here, she added. The number of genetic tests done by KK Women’s and Children’s Hospital (KKH) rose from 900 in 2009 to 1,000 last year. They include a genetic test for a type of thalassaemia, called alpha thalassaemia. This involves extracting and analysing DNA from a sample of blood.

Thalassaemia is a condition in which a faulty gene causes the body to produce too few red blood cells. It occurs in two forms – alpha and beta – depending on which chain of the red blood cell molecules is affected. Each form can be classified as major or minor, based on the severity. Doctors usually ask for it to be done when the patient has a family history of the condition, and when the red blood cells are smaller than usual, said Dr Angeline Lai, who heads the genetics service at KKH’s department of paediatrics. Those who are planning to have a child and have a family history of thalassaemia also go for testing, said Dr Tan Wei Ching, consultant at Singapore General Hospital’s department of obstetrics and gynaecology.

KKH runs the National Thalassaemia Registry, which was started in 1992 and has registered 30,394 patients up to last December. The registry provides free genetic counselling for thalassaemia patients and subsidized screening for their family members, at $15 each.

A type of genetic test, called chromosome analysis, is used to diagnose Down Syndrome, said Dr Lai. This involves studying cells from blood, fluid of the amniotic sac or tissue of the placenta under the microscope to check the number of chromosomes or bundles of DNA. Extracting and testing either amniotic fluid and placenta tissue cost about $600 to $700 in public hospitals. Down Syndrome babies have 47 chromosomes instead of the usual 46. The disorder, which causes learning and health problems, affects one in every 800 babies.

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