Complement mistake in First Aid, or not?

[CW3469]

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First Aid states that deficiency of C5-C8 leads to Neisseria bacteremia. Other sources say C5-C9.

I know in both cases the thing that's defective is the membrane attack complex formation...but the main reason that I ask is that a friend told me on her Step 1 exam a patient presented with a Neisseria infection and she had to pick which complement factor was deficient...Both C8 and C9 were listed as separate answers! (???)

Which answer should one choose if given such a question?

Thanks in advance.

 

[CielloStelatto]

I agree with your conclusion that different sources say different things about C8 +/- C9.

I wonder if there was some other cue in the question stem. Perhaps the patient was Japanese (C9 deficiencies much more common in this population)? That sounds like something the test writers might do. One source beyond what I would expect to show up on the exam (but who knows) suggests that C9 may be important for killing group B strains of N. meningitidis.

 

[kaleerkalut]

First Aid states that deficiency of C5-C8 leads to Neisseria bacteremia. Other sources say C5-C9.

I know in both cases the thing that's defective is the membrane attack complex formation...but the main reason that I ask is that a friend told me on her Step 1 exam a patient presented with a Neisseria infection and she had to pick which complement factor was deficient...Both C8 and C9 were listed as separate answers! (???)

Which answer should one choose if given such a question?

Thanks in advance.

Wouldn't C8 be the safe choice? It is including in both C5-C8 or C5-C9 regardless of who you believe.

 

[je355804]

as goljan says... it doesn't matter. It's the concept that matters. You simply need to know that a lack of the MAC or any of it's components leads to increased risk for Neisseria septicemia.

 

[shenanigi]

Wouldn't C8 be the safe choice? It is including in both C5-C8 or C5-C9 regardless of who you believe.

I have serious doubts that the answer to a question would hinge on C8/C9 out of anything they could ask

 

[kaleerkalut]

I have serious doubts that the answer to a question would hinge on C8/C9 out of anything they could ask

OP stated that C8 and C9 were seperate answer choices. Just going based off that.

 

[FiestyFutureDr]

I have serious doubts that the answer to a question would hinge on C8/C9 out of anything they could ask

I agree that the question stem probably had some other information, since any "late" complement deficiencies will cause these patients to have recurrent systematic Neisseria infections. Typically, the meningococcal infections are with unusual serotypes (W-135, X, Y) rather than typical serotypes (A,B, and C). Now, C8 deficiencies are MUCH more common in the general population, so if the question stem presented no other information, I would definitely have gone with that, but as someone else already noted, C9 deficiencies are disproportionately common in patients of SE Asian descent, particularly Japanese and Korean (in Japan, C9 deficiency is the most common innate immune system deficiency).

 

[gravitywave]

C8 is the bigger offender here and in the absence of other confounders in the stem, you should pick it. the Neisseria defense is hobbled in C9 deficiency but it still works somewhat. OTOH, if they mentioned that the pt was Asian, I would pick C9 in a heartbeat.

 

[kaleerkalut]

C8 is the bigger offender here and in the absence of other confounders in the stem, you should pick it. the Neisseria defense is hobbled in C9 deficiency but it still works somewhat. OTOH, if they mentioned that the pt was Asian, I would pick C9 in a heartbeat.

By the way, where is everyone getting the C9 deficiency is very common in Japanese/Asians? Is this in FA?