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#16 - A common genetic mutation that lowers levels of the

jgabalski
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Can someone please explain #16 to me? When taking this question under timed conditions I chose C, but acknowledge that that was a dumb choice. When I reviewed the question, I was torn between answer A and E and I selected A. I think I chose A because I thought too hard about causality (stablizing cathepsin levels causing the elimination of periodontitis, or something like that)
AthenaDalton
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Hi J,

Thanks for your question!

Let's begin with the correct answer choice, (E).

This argument uses causal reasoning, essentially that:

Restoring enzyme cathepsin C to normal levels :arrow: eliminating periodontitis

This straightforward cause/effect reasoning links cathepsin C with eliminating periodontitis. So the correct answer choice will squarely address this relationship. Answer choice (E) fills in the gap between the cause and effect by assuring us that, once a person's cathepsin C levels reach a normal level, they will not have periodontitis. If restoring the cathepsin C levels did anything other than cure or prevent periodontitis, this researcher's argument wouldn't make any sense.

That's why (E) is an essential assumption underlying the researcher's argument, and why it is the correct answer.

Let's next consider why answer choice (A) is incorrect. The researcher in the stimulus argues that restoring cathepsin C levels to normal will eliminate periodontitis. Would his argument be incorrect if there were another way to eliminate periodontitis? The answer is no. Even if there are two ways of eliminating periodontitis, and the researcher is pursuing one of two possible ways to eliminate this disease, his argument would still be sound. Once he succeeds in stabilizing enzyme levels, periodontitis will be cured. At that point it's irrelevant to his argument if there were an alternate way to cure the disease.

I hope this is helpful!

Athena Dalton
TOgren2424
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I find this problem to be incredibly tricky. I initially chose (D), but think that I understand why (E) is correct and why (D) is incorrect.
Conclusion: Once that happens [researchers develop ways to restore the enzyme Cathepsin C to normal levels--> we will be able to eliminate periodontitis [gum disease]. There are a couple of necessary assumptions in this argument:
1) A person whose level of the enzyme cathepsin C has been restored to normal levels will not suffer from periodontitis [gum disease]. This is answer choice E.
2) There are no other causes of periodontitis other than lowered levels of cathepsin C.

Why answer choice "D' is incorrect:

"Persons who do not have the genetic mutation that lowers levels of cathepsin C do not get gum disease" The issue with this answer choice is its reference to the genetic mutation. Negating this answer choice: "We get persons who do not have the genetic mutation that lowers levels of cathepsin C get gum disease." At first glance, this is tempting. However, it is quite possible that there are other causes of lower levels of cathepsin C besides the genetic mutation and through these other causes people develop gum disease, but still this will be resolved once levels of cathespin C are restored.
However, if the answer choice stated "Persons who do not have lowered levels of Cathespin C do not get gum disease" then it would be correct. Appreciate feedback from anyone on whether this understanding is correct. Thanks!
Jonathan Evans
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Hi, TOgren2424,

Great job! You got this right, and I have very little to add. I would only note that the way you rephrased answer choice (D) to turn it into a necessary assumption ("Persons who do not have lowered levels of Cathespin C do not get gum disease") is in fact just a restatement of answer choice (E)!

Your analysis is sound. Keep up the good work!
TOgren2424
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Thanks Jonathan!
allenxu22
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I understand the explanation for why (E) is a necessary assumption, but isn’t (D) also a necessary assumption under 2) here?

TOgren2424 wrote:I find this problem to be incredibly tricky. I initially chose (D), but think that I understand why (E) is correct and why (D) is incorrect.
Conclusion: Once that happens [researchers develop ways to restore the enzyme Cathepsin C to normal levels--> we will be able to eliminate periodontitis [gum disease]. There are a couple of necessary assumptions in this argument:
1) A person whose level of the enzyme cathepsin C has been restored to normal levels will not suffer from periodontitis [gum disease]. This is answer choice E.
2) There are no other causes of periodontitis other than lowered levels of cathepsin C.


That is, gum disease cannot be eliminated unless ALL causes are eliminated — and it appears that (D) indicates something to this effect. Obviously E is a better choice and the credited one, but could you explain why (D) does not represent 2) above, strictly speaking? Thanks.
Emily Haney-Caron
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Hi allenxu22,

Thanks for the question! This is a tricky one, for the reason you identified. When reading the stimulus, you assumed that the genetic mutation is the only way someone's levels of the enzyme can be lowered, but the stimulus doesn't actually say that. What it says is:
A genetic mutation lowers enzyme levels
Lower levels of enzyme make it hard to fight infection
Raising enzyme levels to normal (whatever the cause of the lower levels) will cure periodontitis

As far as we know, there are several other things that can cause lower enzyme levels, but that's irrelevant for us. Regardless of how the levels got low (genetic mutation or otherwise), making the levels normal will end periodontitis. D, therefore, is irrelevant. An assumption of the argument is, "There are no other causes of periodontitis other than lowered levels of cathepsin C." However, the assumption doesn't extend to anything about why their levels are low.

Does that make sense?
nrpandolfo
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Can't we say that something other than lower levels of the enzyme cause gum disease so even if we bring back levels to normal, we will not be able to eliminate gum disease?
Alex Bodaken
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nrpandolfo,

Thanks for the question! I think you are getting at what is missing from the stimulus...you are right that based on what is in the stimulus, something other than then lower levels of the enzyme could cause gum disease/periodontitis, so we therefore can't prove that restoring the levels of that enzyme will eliminate periodontitis. But that is exactly the missing link that answer choice (E) provides: if it is true that "A person whose cathepsin C level has been restored to normal will not suffer from periodontitis," then we can effectively say that restoring these levels back to normal can eliminate the disease. That is the assumption that we need to add to the argument, and answer choice (E) provides it, making it the credited answer.

Hope that helps!
Alex
rahimlsat
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I still do not understand why A) is incorrect.

Given that this is a CE relationship, I wrote:

Restore CC to normal levels :arrow: eliminate gum disease

According to the LR Bible, in a CE relationship, the author assumes that the cause is the ONLY thing that leads to the effect and the cause will ALWAYS lead to the effect.

So, doesn't this mean that the researchers assume that restoring CC to normal levels is the ONLY way to eliminate gum disease (A).

Can someone please explain? Thanks!