The genetic inheritance of asthma and/or a
predisposition to it is complex. In essence, persons may be born with a
genetic pattern favorable to the development of asthma but never exhibit the outward, clinical expression of it. I believe that description applies to your grandparents who actually did, in effect, genetically pass on the “asthma gene(s)” to your parents or, maybe just to one of your parents for a person with asthma need not get these genes from both parents.