I can tell you how genetic diseases occur. Industrial exhalations in air we breath and radioactivity after catastrophic explosions of nuclear reactors very negatively affect our DNA assembly. Some segments are completely destroyed others are damaged. Therefore some enzymes are not coded correctly and doesn't work properly or doesn't work at all. Allergy is typical of these. Free radicals we inhale must be destroyed within body by action of these enzymes and if these are not available then body must exclude those free radicals through cough, flu....