Vanderbilt U ground-breaking research on how there
Post# of 72440
https://www.nytimes.com/2018/03/15/health/gen...nosis.html
Basically (if you don't subscribe to the Times and don't want to use up one of your 10 free articles per month) -- they did DNA analysis on thousands of patients, then created a database of their symptoms. They then looked to see if people who had the same disease had the same gene mutation -- and indeed it turns out that a lot of diseases DO have a gene involved.
Some diseases that require two copies of a gene to become active (recessive genes) may cause a milder or different form of the disease, later in life, than when the person has two copies of the gene. For instance, some people with asthma may have one of the two genes that cause cystic fibrosis, so they get asthma instead of CF.