A common genetic mutation that lowers levels of the enzyme cathepsin C severely reduces a person' s ability to ward off periodontitis, or gum disease. The enzyme triggers immunological reactions that destroy diseased cells and eliminate infections in the mouth. But researchers are developing ways to restore the enzyme to normal levels. Once that happens, we will be able to eliminate periodontitis.
A person whose cathepsin C level has been restored to normal will not suffer from periodontitis is an assumption on which the argument depends.