By Aisling Brinn
In 1971 the first carrier screening programme for Tay Sachs amongst the Ashkenazi (Eastern European) Jewish population began. Before the programme began, Tay Sachs disease was 60-100 times more common in Ashkenazi Jews than in the overall population. Now more than 45 years later, carrier screening for Tay-Sachs is the longest-running, population-based programme designed to prevent a lethal genetic disease. It has reduced the number of children with Tay-Sachs, born to Jewish parents, by over 90% and has become one of the most successful carrier screening programmes.
Tay Sachs is a fatal disorder that occurs most commonly in children, which results in the progressive destruction of the nervous system. This is due to a mutation on chromosome 15 resulting in the absence of a crucial enzyme called hexosaminidase-A (Hex-A). Without Hex-A, a fatty substance called GM2 ganglioside builds up in cells, especially in the neurones of the brain. This accumulation causes progressive damage to the cells. Although this destructive process begins early in pregnancy, a baby born with the disease appears normal until 6 months old when their development slows. By the age of two most children are experiencing seizures and reduced mental function. The child continues to gradually regress and becomes unable to crawl, turn over or sit and eventually becomes blind, cognitively impaired, paralysed and non-responsive. The nervous system becomes so badly damaged that death usually results by age five. There is no cure or effective treatment for this disease.
The mutation is inherited in an autosomal recessive pattern, if both parents are carriers their child will have a 25% chance of inheriting Tay-Sachs disease, and a 50% chance of becoming a carrier. Although, some non-Jewish individuals are carriers, the incidence is significantly higher in people of Ashkenazi Jewish descent. Approximately 1 in 27 Ashkenazi Jews are carriers compared to 1 in 250 in the general population. Carrier screening for Tay Sachs is provided by the NHS for anyone of Ashkenazi Jewish descent, as well as those with a family history of the condition. The screening test involves taking a blood sample and using either an enzyme assay to measure levels of HEX-A in the blood or a HEXA DNA common mutation assay. Almost all Ashkenazi carriers can be detected by screening for three known mutations in a DNA assay and this method of testing is preferred as it is more cost-effective in an Ashkenazi Jewish population.
Part of the success of this screening programme was due to the effective education of the at-risk population, and of religious leaders which led to wide acceptance of carrier screening. Many groups advocated for comprehensive testing and prevention resulting in a high uptake of screening by the population. Confirmed carriers can reduce their risk of having a child with Tay Sachs disease by avoiding marriage to another carrier or, if already married, by opting for prenatal diagnosis and termination of the pregnancy.
In some Jewish communities, particularly the strictly Orthodox, the international Dor Yeshorim programme is used, which provides pre-marital compatibility testing prior to arranged marriages. An individual will be tested to determine their carrier status for Tay Sachs and several other conditions, each individual is then given a PIN. When a couple are considering marriage, they notify Dor Yeshorim and provide their PINS before being informed if there is a problem or not. If both are carriers for the same condition it is considered advisable to end their relationship, hence this check is performed early to avoid disappointments. This system has the approval of many prominent halachic authorities, and has helped overcome a hurdle in the implementation of population screening, by providing an option that was acceptable to Orthodox Jews (although this system does have critics within the Jewish community). This example illustrates that a successful population-wide screening programme is possible if implemented with sensitivity and respect for cultural and religious differences.
The success of this screening programme is unquestionable, today the majority of children born with Tay-Sachs disease have non-Jewish parents.