Original
It is my belief that it is possible all of the listed causes. Genetics has played a big roll in my family's over all health and birth defects. Environmental reactions and sensitivities have been a cause of much sickness in my life. I have suffered from severe sinuses infections, bronchitis and pneumonia, from reactions to chemicals in the air that I breath since about age 25. I don't know yet what the medical science says concerning the cause, I would suspect it would be different for each case.