Ashkenazi Jews originated in Eastern Europe but are now dispersed throughout the world, and comprise 80 percent of the world's Jewish population of 13 million. Ashkenazi Jews have historically been endogamous for a number of reasons. Early Jewish settlers in Eastern Europe often lived in small geographically isolated villages (called 'shtetls') composed of a few families. Jewish culture and religion encouraged separation from the secular world, and endogamy was an important mechanism to achieve this objective.
Ashkenazi Jews were further geographically and culturally isolated as a result of state-mandated discrimination, which often forbade marriage to non-Jews. One consequence of this particular history is that Ashkenazi Jews have an increased risk of certain genetic diseases, such as Tay-Sachs. This is attributed to genetic drift and the founder effect. The founder effect occurs when a population has a small number of founding members, one of whom carries a particular genetic mutation. Genetic drift refers to the random chance that any such individual carries a mutation. As the population increases in size, the mutation will increase in frequency especially if the population remains reproductively 'closed' for example due to endogamy. Reproductive closure limits gene flow with outsiders who may introduce genetic variation.
Screening programmes and research centers for 'Ashkenazi Jewish genetic diseases' exist throughout the world. As a result, the incidence of Tay-Sachs and other recessive diseases have been greatly reduced. While genetic testing and screening programmes have primarily been for recessive diseases, in the mid 1990s Ashkenazi Jews were discovered to have the highest known population risk of carrying dominant mutations in the BRCA1 or BRCA2 genes. These mutations confer a significantly increased lifetime risk by up to 85 percent of developing breast and/or ovarian cancer.
Let us return to the original question, why might an Ashkenazi Jewish woman suggest marrying out? Some Ashkenazi Jewish women at increased risk of BRCA1/2 mutations suggested marrying out as a strategy to reduce the incidence of breast cancer in future generations (1). Endogamy among Ashkenazi Jews is a well-known and accepted part of collective history, and one which is often referred to in terms of cousin marriage. At the same time, women attributed the increased risk of genetic disease to this history of endogamy. Women recognised that the idea of marrying out could be problematic given the importance many Jews still place on endogamy. However, for those women with personal and often devastating experiences of breast cancer in the family, the suggestion to marry out reflected their strong desire to protect their children from facing breast cancer in the future.
While marrying out could potentially reduce the overall population risk of BRCA mutations over time, for those women who are carriers, their own children's risks unfortunately cannot be reduced this way because the genes are transmitted in an autosomal dominant fashion. Unlike recessive diseases, such as Tay-Sachs, which are only manifested when a child inherits two copies of the recessive alleles from their carrier parents, with BRCA1 or 2 the child of a mutation carrier has a 50 percent chance of inheriting the mutation regardless of their choice of marriage partner. Women's recommendation to marry out does not therefore reflect an accurate distinction between dominant and recessive inheritance patterns; rather it reflects their desire to protect their children. It is likely that the success of Tay-Sachs screening, and women's familiarity with it, have influenced how genetic breast cancer transmission is understood.
Women's suggestion to marry out provides an interesting example of the culturally specific, and perhaps surprising, ways in which knowledge of genetic disease risk can be interpreted by some members of a high-risk population. It is essential that we examine the unique cultural context in which genetic information is interpreted because, as this example demonstrates, ethnicity, understandings of collective history and prior experiences with genetic screening can have an impact on how genetic information is understood.