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This one is about: Incidents of Clefts Among Races
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Incidents of Clefts Among Races, Comments by Joanne Green
I have heard theories, but I believe no one knows for sure.
First, it is true that clefting happens more often proportionately among Asians (one in 500) and least often in persons of African heritage (one in 1,000), and one in 700 among persons of European ancestry. The Asian group includes American Indian and Hispanic. Here are the 3 theories:
1) Heredity. They think that, like Tay Sacs or Sickle Cell anemia, clefting may be associated with genes that are associated with the child's ethnicity. However, it does happen way too often in all races for that to satisfactorily answer the question.
2) Face shape. The shape of the front of a person's face is somewhat race-specific. The thought is that because Asians have a flatter facial plane, they are more susceptible to clefting. The problem with that theory is that it would then make more sense that the Europeans, with the more angled plane (ie, bigger noses) would be the least affected. That is not the case.
3) Environmental factors. The theory is that socioeconomically those of Asian, Hispanic and Native American tend to have fewer resources, poorer prenatal care, etc. Many Asian and South American countries are the poorest in the world, and nutrition is very bad. Even in the US those groups are disproportionately representative of the nation's poor. Again, the problem with that theory is that there are some very poor African nations too, and African Americans are also among the American poor as well.
Those are the theories. Each one has its merit and each one has its problem. I personally think that it is a combination of the 3. Heredity (including facial shape) and environment. And I think that persons of African heritage, although they inherit sickle cell and high blood pressure, they get a break when it comes to cleft. But it still happens in that population too.
So there's the answer - I don't have an answer. (Hey - - it can happen!)
Also noted By Sharon Dietch: It's higher in Israel (1/500 as opposed to 1/700 worldwide), but I think that's because of the high birth rate among the Arabs and the ultra-Orthodox.