The successful use of gene probes for diagnosing inherited disease in the first nine or 10 weeks of pregnancy raises more important social implications than technical ones, Dr Bernadette Modell, consultant in perinatal medicine at University College, London, told the British Association meeting at Strathclyde University yesterday. A genetic health education program, with the offer of testing, genetic counselling and information, was needed, she said.
Modell was speaking about an international trial of a new technique known as chorionic villus sampling, in which less than 50mg of a sample from the womb is enough for an examination of the complete genetic make-up of the fetus. She said that the technique should become applicable to most forms of genetic diagnosis.
‘Gene probes’ is the shorthand description for the bio-chemical trick in the laboratory of producing a map of the genes in the strands of DNA to identify any defects.
Dr Modell focused on the implications for two blood disorders, sickle cell anemia and thalassaemia.
She described them as among the most treatable and preventable of common inherited disorders. There was evidence that the first could largely be avoided by neo-natal diagnosis and the use of simple protective measures from the first months of life.
Thalassaemia could be treated by monthly blood transfusions, combined with daily infusion of the iron-helating (something that combines with iron) agent desferrioxamine. It was effective and cost about pounds 4,000 a year for a healthy life for each patient.
Most of the disorders were due to the absence of some biological entity in the body, for which drugs were usually ineffective and treatment requires some way of substituting the missing molecules.
‘Since treatment stops patients dying, while others continue to be born, the number of patients to whom treatment can be delivered increases steadily, while at the same time the amount to be done for each patient usually increases as treatment improves, and this can lead to important problems of implementation,’ she said.
Dr Modell gave as an example the incidence in Cyprus of thalassamemia among children who began regwar transfusions about 20 years ago. Their numbers increased so fast that eight years later it was predicted that in a further 20 years, 40 per cent of the island’s population would have to donate blood once a year for thailassaemia alone.
Health service costs would soar to pay for hospital treatment for the disease alone unless there was some form of prevention. Genetic counselling had alleviated such a dilemma.
Dr Modell said that the prevention of birth of children with thalassemia depended on the fact that it was possible to diagnose carriers before they had any affected children.
People needed to know whether they had an avoidable risk either very early in pregnancy, or preferably even before they had received at all. But ‘premaritaltesting was not generally practiced in north European countries, she said, although it was becoming widely available in the Mediterranean area.