19 May 2009
Tay Sachs disease (TSD) is an autosomal recessive genetic disease caused by mutations in the hexosaminidase A (HEXA) gene; it results in progressive neurological degeneration. The most common form of TSD is lethal in infancy or early childhood, and there is no effective treatment. However, biochemical or molecular (DNA) testing is possible and can be used to identify unaffected carriers at risk of passing the disease on to their children.
Although TSD is a very rare disease, with the carrier frequency in the UK general population only around 1 in 250-300, this figure is substantially increased in Jewish populations of Ashkenazi origin (those originating from Central or Eastern Europe). Here, the carrier frequency around ten times higher at around 1 in 25-30, due largely to three specific mutations. Carrier screening for TSD in the Ashkenazi Jewish population is therefore feasible, and screening programmes have proved highly effective in reducing the prevalence of TSD. Carrier testing been funded by the National Health Service (NHS) since 1999 in the UK. If two carriers wish to have children together then advice from clinical geneticists would be recommended, since there is 25% chance that their children will have TSD.
In a project commissioned by the UK Newborn Screening Programme Centre (part of the National Screening Centre), the PHG Foundation worked with Guy’s and St Thomas’ Clinical Genetics Service in London and an expert Advisory Group to undertake a needs assessment and review of current TSD screening services in the UK. The final report from this project, Tay Sachs Disease carrier screening in the Ashkenazi Jewish population, is now available, and sets out the findings and recommendations from this work.
The UK Jewish population is relatively small at around 270,000, many living in areas of London and Manchester. The report authors found that carrier screening currently takes place in different contexts: outreach community screening is provided on a voluntary basis by Jewish charities in selected schools, universities and community centres. Testing for carrier status in may also be accessed via clinical genetics services, two walk-in clinics in London, and from the antenatal setting, with the actual testing being performed at NHS laboratories in London (Guy’s) and Manchester (Willink). However, there is a lack of systematic screening provision. A survey of antenatal screening in 114 hospital trusts showed that screening was not routinely offered, even in areas with large Jewish populations, and there was confusion as to which women ought to be offered testing.
In fact, patient surveys revealed a good level of awareness of Ashkenazi Jewish ethnic origins; 97% of respondents had four Jewish grandparents, but they had mostly heard about screening from family or friends or via the internet, rather than as part of their antenatal care or from a health professional. One third of patients undergoing testing who were interviewed were already pregnant. The report concludes with a set of recommendations that could be used to strengthen the NHS carrier testing offered to the UK Ashkenazi Jewish population, which could also be relevant to screening provision in other countries.
Referring to the report, Dr Ian Ellis, Consultant Clinical Geneticist at the Alder Hey Children's Hospital in Liverpool and member of the expert Advisory Group for the project commented: “People have to realise that Tay-Sachs has not gone away, but only through constant vigilance and screening can families be made aware of the potential risk and their options. This report documents the previously haphazard arrangements for Tay Sachs screening in Britain. The report is comprehensively written and provides an opportunity for building Tay-Sachs screening into current NHS screening plans”.
Dr Anne Mackie, Programme Director for the UK National Screening Committee, stated: "The UK NSC believes that antenatal Tay Sachs testing should be available for individuals from high risk populations - including the Ashkenazi Jewish population - who seek it. We are asking NHS commissioners to assess the need for this service in their area and provide a service to those who have a reason to seek it". See also NSC policy position on Tay Sachs disease screening in pregnancy; this refers only to antenatal and not community screening.