by Eliana Solaimani, Summer Work Experience Student
One of the most important concepts in genetics and evolutionary biology is the founder effect. The founder effect occurs when a small group of individuals breaks off from a larger population to establish a new community. The new community could form for a multitude of reasons, such as migration to a new area, climate change separating a population, or geographical changes physically separating a group. This small ‘founder’ group carries only a fraction of the genetic diversity of the original population, meaning the new population has a reduced genetic variation. Consequently, if there is a mutation leading to a genetic disease in the larger population, it is more likely to be passed on and increase the frequency of certain rare disorders in the new population, as it now makes up a higher proportion of the DNA of this new group.
Throughout history, the Jewish people have experienced numerous events that lead to their population being dispersed, giving rise to the founder effect. Ancient dispersions, such as the Babylonian and Roman exiles, scattered Jewish communities across different regions, resulting in isolated populations. This isolation lead to the formation of distinct offshoots of the Jewish community, namely Ashkenazi, Sephardi, and Mizrahi communities.
The founder effect is evident in the differing genetic profiles of these communities. Certain inherited disorders, such as Canavan Disease, are predominantly found in Ashkenazi Jews, while other disorders, like Tay-Sachs Disease, are present in Ashkenazi, Sephardi and Mizrahi populations. These genetic differences illustrate the impact of historical dispersions and isolation of the Jewish people, as well as when these diseases first appeared in the genome of the Jewish community.
Additionally, events like the Spanish Inquisition in 1492 forced Jewish communities to relocate and form new, smaller populations, increasing the proportion of mutated genes. Jewish communities have also kept themselves reproductively isolated from surrounding populations, helping to maintain their distinct genetic makeup, which is both cultural and religiously based endogamy.
The bottleneck effect has also significantly affected Jewish populations. The phenomenon occurs when a population is drastically reduced in size due to events such as in natural disasters or habitat loss. Violent anti-Semitic events, such as crusades, pogroms and the Holocaust, significantly reduced the size of many Jewish populations, leading to a genetic bottleneck. This loss of genetic variation results in a higher proportion of mutated genes, making the Jewish people more vulnerable to genetically inherited disorders.
Due to Jewish populations historically forming isolated communities with limited genetic diversity, certain genetic traits and diseases have become more prevalent within these groups. For example, cystic fibrosis, caused by a recessive gene, is a progressive disorder associated with the build-up of thick mucus in the lungs and digestive system. This leads to symptoms including chronic respiratory infections, lung damage, poor growth, pancreatic issues, and infertility in males.
Additionally, the dominant BRCA1 and BRCA2 mutations are found at higher frequencies in Jews. Approximately 1 in 40 people of Ashkenazi Jewish origin, and 1 in 140 people of Sephardi Jewish origin, have a BRCA gene mutation compared to 1 in 250 people in the general population. These mutations significantly increase the risk of breast, ovarian, prostate and pancreatic cancers. Consequently, individuals with Jewish ancestry (i.e. at least one Jewish grandparent) have an increased risk of having a BRCA gene mutation, which in turn raises their risk for developing several types of cancer.
Fortunately, the risks for developing these cancer types and other inherited genetic disorders can be managed if you are aware that you have a mutation, and anyone with Jewish ancestry can now be screened through the NHS Jewish BRCA Testing Programme.
At Jnetics, we offer genetic screening programs for 47 genetic disorders common in the Jewish population to help manage and prevent these conditions. Understanding the founder effect and its consequences in Jewish populations has significant implications for genetic research, genetic counselling, and personalised medicine, contributing to the mission to increase quality of life, and ultimately save lives.
