Why do Jews have so many genetic disorders?
Everyone, no matter what their ethnic background, is born with several gene faults that can cause a health problem. These gene faults may be passed down through the family.
Some families have gene faults that are not common in others. Jews are like a large family- they commonly share some genetic traits that are rarely found in non-Jewish families. It is not known why certain gene faults are more common amongst Ashkenazi Jews than other populations.
Some gene faults become more common because of a secondary beneficial effect, but no benefit of carrying BRCA gene faults has been found. It is more likely a chance effect that these gene faults became more common amongst the Eastern European Jewish community.
Research has shown that some of these gene faults have been present amongst Jews since before the destruction of the second Temple, and are found in many Jewish communities, not just Ashkenazim.
Jews are not unique in having genetic conditions related to their ancestry. Many populations who have a shared ancestry also have shared genetic faults. This is particularly common where outsiders don’t commonly marry into the group, due to religious practice or to physical isolation.
No matter what our ethnic background, we all carry many faulty genes which may cause disease. People of a shared background tend to carry the same faulty genes as each other, but do not have more faulty genes than any one else.