In the beginning, God did not make people to be deffective.  They were formed in His image, and therefore, perfect.  Over time, we have sinned and our birth deffects are a result of this sin along with poor diets and a bunch of other stuff we have brought on ourselves.  Haven't you noticed that new diseases are being discovered all the time.  Then once they are discovered, it is just a matter of time before we find them everywhere.  Some are from enviromental factors such as pollution.  Others are from the junk we put in our food, like preservatives.  And don't even get me started on prescription drugs.  We have doctors telling us to put poisons in our bodies, in the name of medicine, all the time!