PT59, S3, Q16 - A common genetic mutation that lowers levels

[steven.kantowitz]

Aren't both D and E necessary assumptions for the argument to hold true?

If D were false, and regular people could develop gum disease, then periodontitis would not be elimited. The only way I see that D could be wrong is if you claim that the enzyme automatically prevetns gum disease, in which case you could just pump the enzyme into their bodies...?

[noah]

Another tough one!

The conclusion is that once researchers develop ways to restore enzyme C to normal levels, we'll be able to eliminate periodontitis. Why? Because enzyme C does stuff that kills bad things in the mouth. The first sentence is not part of the argument's core.

We're looking for a necessary assumption. This means the negation test will be very useful. It's also useful to notice that there's a jump from the enzyme doing it's thing in our mouth to periodontitis being eliminated. We should be wary of such a strong conclusion. Will it be completely eliminated? What if people who have lots of this enzyme C develop it for another reason? (E) fills this gap. It is necessary, because it we were to negate it - a person with enzyme C can suffer from periodontitis - the argument doesn't make sense.

(A) is incorrect because it's not problematic if there's another cure for periodontitis, such as world-wide mouth bleaching.

(B) is tempting -- what if there's another cause of lower enzyme C levels? -- however, we're interested in whether when we can raise those levels will periodontitis be eliminated, not how did those levels drop in the first place.

(C) is irrelevant - we're not interested in when this oral breakthrough will occur.

(D) is quite tempting. It seems to be saying that we don't need to worry, there are not many ways to get to gum disease, it has to be that drop in the enzyme level. However, it does not say that. It says, there are not many ways to get gum disease other than that genetic mutation. If we negate it, we would face this fact: people without that mutation can get gum disease. Perhaps those folks have some other route to lower levels of enzyme C, which then causes the disease. In which case, the conclusion still might work.

Does that makes sense?

Formally:

[~ C --> higher risk of perio.] not essential to the core
high C --> ~ bad mouth things
Therefore high C --> ~ perio.

We need ~ bad mouth things --> ~ perio, which (E) provides.