Ethnicity and Genetic Diseases
Ethnicity vs. Expanded Carrier Screening
There are two approaches to carrier screening: ethnicity-based screening and expanded carrier screening.
In ethnicity-based screening, you are tested for disorders based on your ethnicity or family history. This is the way all carrier screening of the Jewish population was done in the past. In the 1970s there was only one test available, an enzyme screening for Tay-Sachs disease for Ashkenazi Jews only. As discoveries about the genetic cause of the diseases evolved, the list of disorders, called a test panel, for which all Jews could be screened, consistently improved.
Over time, however, we have learned that ethnicity-based screening has many limitations. Today with expanded carrier screening, many disorders can be screened for without focusing on either race or ethnicity. Most national genetics and reproductive medicine societies support the use of these expanded carrier screening panels for all individuals. As a result, highly accurate carrier screening is now available for Jews of all backgrounds, as well as people of all ethnic backgrounds.
Expanded Carrier Screening
From the beginnings in the 1970s, when the only test was an enzyme screen for Tay-Sachs, the list of diseases for which screening is available has continued to rise and more accurate testing has been developed through sequencing as genetic science has evolved.
Individuals should do expanded carrier screening to include disorders not necessarily more common in people with their ancestry (Pan-Ethnic Panels). Any of these diseases may appear in people of any ethnic background.
Why are mutations in certain disease genes so common among people of certain ethnic groups?
There are several theories about why severe, recessively inherited genetic conditions are common in certain populations. One is the founder effect, where a mutation occurs in an individual who becomes isolated from the larger group due to migration (founding a new Jewish community elsewhere) or a sudden decrease in population size, such as a pogrom. As this person reproduces in a small group the mutation increases in frequency. As with the Eastern European Jews, the isolated group intermarries and the mutation becomes even more concentrated.
The founder effect also affects other ethnic groups, not only the Jews. For example, Sickle Cell Anemia in the African American Population and Tay-Sachs can also be found in other ethnic groups such as French Canadians and Cajuns from Louisiana.
Another theory is called selective advantage and this suggests disease protective effects of mutated genes as we see In sickle cell anemia carriers and malaria or Tay-Sachs carriers protected from tuberculosis.