Familial Dysautonomia (aka Riley Day Syndrome) is a very rare, predominantly Jewish Genetic disease that is considered to be autosomal dominant. Which means both parents must carry the disease in order for it to be transmitted to children.
It is a disease that effects the autonomic nervous system and basically causes the whole thing to malfunction.
The symptoms of FD are, among others, the inability to control body temperature, blood pressure, and all other functions that are controlled automatically in normal health children.
These kids have no reflexes, have major trouble swallowing food, cannot feel pain, have no taste buds, do not produce tears, have difficulty swallowing without misdirecting food to the lungs, have delayed growth and development, delayed speech, can have fluctuations of body temperature from 94-107 degrees F. in a matter of minutes, are very prone to aspiration pneumonia and a few hundred other symptoms too numerous to list.
There are now prenatal tests available to screen for FD, and in my opinion, any couple of Ashcanazic Jewish descent should be tested before having kids with the appropriate genetic counselling.