Is diagnosing Tay-Sachs disease really a simple blood test? The answer is yes if you know what you’re looking for. Most families with a Tay-Sachs child in 2010 would say it was not just a simple blood test. Why? There are a number of reasons. The first two will be discussed in this article.
First, Tay-Sachs is extremely rare. If a child presents to his or her pediatrician with low muscle tone, for example, the pediatrician is not running to do a Tay-Sachs test. There are so many more common causes of low tone. Rare genetic diseases such as Tay-Sachs are close to the bottom of the list, particularly if one is not of Ashkenazi Jewish decent. As the pediatrician works his or her way down the list of possibilities, specialty consultations are being arranged, such as Neurology and Genetics. Then there is the wait for those appointments. It could be 9 months before an assessment is scheduled in either of these two sub-specialties.
Second, Tay-Sachs is no longer only a Jewish Genetic Disease. This is due to highly effective genetic screening of the Ashkenazi Jewish population since the early 1970’s. Tay-Sachs screening did not eradicate Tay-Sachs in Jews. Screening did, however, cut down the incidence of Tay-Sachs in Jews by a whopping 90 percent, from 60 new cases per year in the United States and Canada before 1970, to 3 to 5 new cases per year in the early 1990’s.
Can Ashkenazi Jews still get Tay-Sachs? Absolutely. One reason for this is that not all Jewish people get screened or know to get screened. Second, a small number of Jews that are screened receive false negative results due to a lab error. A third reason is that many people do not know that they have an ancestor of Ashkenazi Jewish decent and so screening never comes up. The disease is passed on by a recessive gene, which means the gene for Tay-Sachs can be passed from generation to generation, never manifesting any symptoms.
As Tay-Sachs screening reduced the incidence of new cases in the Jewish population by 90%, other high-risk ethnic groups have emerged and their unique genetic mutations identified. These groups include Irish Americans, in which one in 50 are carriers of the Tay-Sachs gene, and French Canadians and Louisiana Cajuns, who have the same carrier rate as Ashkenazi Jews, which is one in 27. The carrier rate for the Tay-Sachs gene in the general population is one in 250. Medical texts still emphasize the Ashkenazi Jewish predominance, and therein lay a major problem in preventative or prenatal screening of the other high-risk ethnic groups.
A third reason why a Tay-Sachs diagnosis is not just a simple blood test involves the hidden symptoms which often go unreported until it is too late.