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Comments ...

 +9  (nbme24#13)

These kinds of questions are really hard because I've never seen female reproductive structures irl. :c

nbmehelp  Lmao

 +2  (nbme21#20)

Because his testicles are undescended, his sertoli cells are probably not working properly, and therefore not synthesizing MIF correctly. Which is why his internal female genitalia is allowed to develope in a default setting.

Subcomments ...

Oral vesicle (hint hint). Blistering vesicular lesion on the hand. No fever, not toxic-appearing. This is Herpes (you may remember dentists getting herpetic whitlow in your studies, which is what this is). Most folks get HSV1 as children, though obviously not all are symptomatic. HSV is a large double-stranded, linear DNA virus.

jiya   why cant this be hand foot and mouth disease cause of coxsache +1  
drachenx  Also thought it was Hand-foot-mouth an RNA virus but I did consider Herpes. Changed because I thought Hand foot and mouth would be more common. +  
llamastep1  Hand foot mouth usualy involves all 3 places (hands, feet and mouth/perioral area) and the lesions on the hand arent localized to just one finger. +  
aneurysmclip  Hand foot mouth disease affects palms and soles. ref: FA 2019 - 150 +  

submitted by drdoom(354),

Here’s one way to process-of-eliminate “decreased hydrogen-bond formation”: I’m not a big fan of this line of reasoning, but technically alanine as a side group has more hydrogens* for potential hydrogen bonding than glycine:

alanine: —CH3
glycine: —H

So, “technically,” alanine would permit more hydrogen-bond formation, which might allow you to eliminate that choice.

That said, it seems almost impossible to rule out (without very technical knowledge or some provided experimental data) that the slightly larger alanine does not impair hydrogen bonding between collagen molecules via steric (spatial) interference. In simpler terms, since alanine is larger, you would think that it must somehow interfere with the hydrogen-bonding that occurs with the wild-type glycine.

*Strictly speaking, it’s not the number of hydrogens but also the strength of the dipole that facilitates hydrogen bonding: a hydrogen bound to a strongly electronegative molecule like fluorine will “appear” more positive and, thus, hydrogen-bond more strongly with a nearby oxygen (compared with a hydrogen connected to carbon, for example).

Further reading:

  1. https://www.chem.purdue.edu/gchelp/liquids/hbond.html
hungrybox  Appreciate the effort but this is far too long to be useful. +7  
drachenx  hungrybox is a freaking hater +  
drdoom  @drachenx haha, nah, coming back to this i realize i was probably over-geeking lol +  
blueberrymuffinbabey  isn't the hydrogen bonding dependent on the hydroxylated proline and lysine? so that wouldn't really be the issue here since those aren't the aas being altered? +  
drdoom  @blueberry According to Alberts’ MBoC (see Tangents at right), hydroxylysine and hydroxyproline contribute hydrogen bonds that form between the chains (“interchain”, as opposed to intra-chain; the chains, of course, are separate polypeptides; that is, separate collagen proteins; and interactions between separate chains [separate polypeptides] is what we call “quaternary structure”; see Tangent above). And in this case, as you point out, the stem describes a Gly->Ala substitution. That seems to mean two things: (1) the three separate collagen polypeptides will not “pack [as] tightly” to form the triple helix (=quaternary structure) we all know and love and (2) proline rings will fail to layer quite as snugly, compromising the helical conformation that defines an alpha chain (=secondary structure; the shapes that form within a single polypeptide). +  

submitted by yotsubato(519),

Why is this NOT chancroid? Theres nothing here that rules it out.

drachenx  Chancroid is described as an ulcer.. whilst in this question they mentioned "vesicles". Pretty much only herpes is vesicular +5  
whoissaad  They mentioned ulcers too. I chose chancroid as well, couldn't find a clue to rule it out. Also thought "discharge" was pointing you towards a bacterial infection. But guess I'm wrong :) +  
emmy2k21  I think NBME/USMLE writers make the assumption the patient is in America unless specified otherwise. Chancroid is not common in the US. If the question stem mentions a developing country, then chancroid can make your differential list. +1  
selectuw  for chancroid, there may be a mention of inguinal lymphadenopathy +2  
samsam3711  Also with chancroid questions they want you to differentiate it between chancroid and syphilis, (eg. Painful vs. painless) and is usually described as a much larger ulcer that is painful (not vesicular as in this question) +  
suckitnbme  Also believe that chancroid does not presents with systemic symptoms like in this vignette. +  

submitted by neonem(366),

This is a case-control study because it selects first by disease outcome (intellectual disability) and then retroactively looks at exposure/risks (TV usage). Odds ratios are used to evaluate case-control studies; if there was a positive relationship between TV use and intellectual disability, the OR would say something like "Children with intellectual disabilities were 3 times more likely to have 2 or more hours of TV time per day than children without intellectual disabilities."

Relative risk is used for cohort studies, which first define an exposure (TV use) and then look at the outcome (Intellectual disability). A relative risk would be more like "Patients with 2+ hours TV/day are at 3x higher risk to develop intellectual disability than children with <2 hours."

Typically, OR and RR are similar numbers but that assumption breaks down at a certain point, I think when the disease is very rare or something.

drachenx  Following up on Neonem's comment OR = RR when you are dealing with a RARE disease. +3