UWorld Step 1 Qbank: Your world of learning.
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(nbme21#39)

If u are not goot in math like me xD. I did it this way: They gave me p^2=1/900 so p=1/30.

Now I need to find P, so use p+q=1. p= 1-(1/30)= 1-0.03= 0.97

So, 2pq= 2(0.97)(0.03)= 0.064 = (1/15) :D I got it right, this is my way to do it cause im not good at fractions.

eacv  **** q=1/900
bdaines8  you literally have a calculator to use.... use it

(nbme21#50)

here is also a picture about the veins and proximity to the lungs

https://ars.els-cdn.com/content/image/1-s2.0-S0007091217327587-gr1.jpg

(nbme20#8)

This is an AORTIC DISSECTION: No. 1 RF is HTA, intimal tear forming a false lumen and the pain sudden onset radiates to the back.

(nbme20#40)

to add : it also ARISE FROM BRONCHUS and that is described in the qx.

(nbme20#16)

Informed consent should be obtained by a provider who has sufficient knowldge to give accurate description of the intervention, the riska and benefits of tratment, and able to answer all of the px question. This is the explanation for a very similar qx in Uworld.

submitted by jooceman739(20),

Retinoblastoma:

The physician said the boy is unlikely to develop any other neoplasms, so he doesn't have the inherited Rb mutation.

In this case, he has the sporadic retinoblastoma. Sporadic retinoblastoma requires two somatic mutations of Rb in the same retinal cell.

Just as a side note: Inherited retinoblastomas tend to be bilateral. Sporadic are unilateral.

carls14  aren't retinal cells a type of somatic cell? Why not is the mutation not considered in the somatic cell of the child? +5
omerta  Although this mutation would be considered somatic, I believe the question is just asking you to be specific as to which cells. If you answered "somatic cells of the child," that's quite broad and could apply to almost anything. +7
kernicterusthefrog  I had the same struggle and thought process. +1
eacv  There is a Uworld qx that explain this in detail> ID: 863 +3
arcanumm  I read the answer options too fast so got this wrong. It is a somatic cell type, but somatic in general implies a higher risk for developing other cancers. The hint here is that the physician stated he is unlikely to develop any other neoplasms, so it is a specific double hit mutation in the retina. +2
almondbreeze  wouldn't she have any possibility of developing osteosarcoma as well? :( +
almondbreeze  did some reading and it seems like osteosarcoma only occurs in familial retinoblastoma with RB mutation +

submitted by bubbles(51),

For the peeps who got confused on this question bc of UWorld's weird question on HIV viral load:

acute HIV-1 infection: HIGH viral load, low Ab HIV-2 infection: LOW viral load, low Ab (bc standard HIV assays detect p24, which is not present on HIV-2)

Kinda annoyed I missed an easy immunology concept question :/

eacv  I feel you my friend! same stupid mistake over here -.- +1
step1soon  FA 2019 pg 176 +1

How many people didn't see that it was 1-specificity and picked E like me :(

jfny21  Here +1
eacv  yesss! me too -.- +1
jinzo  me also :( +1

submitted by sacredazn(59),

The concept is a convoluted way of asking if you knew how VDJ recombination works, which is that it is actually an example of altering the DNA of the B/T lymphocyte.

Southern blot technique: So when they use a probe against some region, and outputting a size of 1.5 kb or 6 kb, this is telling you the size of the DNA fragment in each cell (doesnâ€™t matter if they say J probe or constant region probe, theyâ€™re just saying theyâ€™re targeting some nucleotide sequence found in the Ig locus/TCR beta chain locus respectively for B/T cells).

I think the confusing part could be wondering how you know whether youâ€™re partly through rearrangement (answer choices B thru D) or if it hasnâ€™t occurred at all yet (correct answer). Here, the concept is that B cells undergo V(D)J rearrangement in the bone marrow, while T cells do it in the thymus, and it all happens at once. So a plasma cell in the blood like in Multiple Myeloma would have fully undergone recombination, while a T cell in the blood could either be fully educated (and have finished VDJ recombination) or immature (hasnâ€™t started VDJ).

Since the T cell gene was 6 kb and definitely bigger than the 1.5 kb gene, the T cell hasnâ€™t undergone recombination yet.

trichotillomaniac  very nice explanation! +7
nwinkelmann  This was awesome! Made so much sense and hopefully I will be able to think that critically about questions in the future (because I NEVER would have come up with this on my own, hah). +4
eacv  OMG! THANK YOU. I DIDNT KNOW ANYTHING about this!! Hope this is not testesd on real examen :p +3
ribosome01  I would like to meet you personally and say thank you I wish I had a teacher like you +
ajss  wow! this explanation was awesome! thanks! +
mrglass  Also the T-cell V-D-J segments are not the same as the B-cell V-D-J segments. Therefore a B-cell J segment southern blot would look for whether the B-cell site VDJ segment in a T-cell, which would always non-rearranged. +4
mynamejeff  Thank you! So is this because multiple myeloma produces excessive monoclonal light chain Ig? Is this the 1.5 kb gene? Whereas, T-cells that have not gone through differentiation yet and their J region includes everything (VDJ) vs. just VJ in the light chain? (FA 2020 pg 104) +
peridot  This explanation is amazing! However, to fully understand another step of what the question is getting at, please take a look at @highyieldboardswards's and/or @mrglass' explanation as well - a very important addition!! +

submitted by cantaloupe5(61),

Proccess of elimination for this one. Two you can eliminate immediately just from looking at the biochemical pathway chart. The other two required knowledge that eumelanin is more protective than pheomelanin (this is why redheads burn more easily). Because pheomelanin is less protective, there would be more not less ROS from sunlight.

henoch280  @temmy. This question tests our knowledge on albinism which is normally a tyrosinase deficiency disease but the vignette states that the boy's albinism is caused by a genetic mutation in the TYRP1 gene which is shown in the biochemical pathway. A gene that helps in the synthesis of Eumelanin. Now you have to understand that all precursors before that gene is the pathway would still be available if not increased which make 2 of the options in the question wrong. you also have to understand this: (Eu)melanin = (normo)melanin i.e normal melanin which is protective to the skin, decreases reactive oxygen species and gives the dark pigments to the iris, choroid, skin, hair e.t.c. while (feo)melanin = (fake)melanin i.e pheomelanin, the one present in our patient here which is less protective again the uv rays, cannot pigment and cannot decrease ROS generated in the skin. i hope this helps +16
eacv  @henoch280 thank u very much! I got it right by luck but now i do understand :D +

euthyroid sick syndrome is sometimes called "low T3 syndrome." Also you know that the patient is euthyroid because her T4 and TSH are within the reference range. She is sick.

yotsubato  This is not in FA btw. +7
niboonsh  https://www.ncbi.nlm.nih.gov/books/NBK482219/ probably caused by her recurrent pneumonia +3
eacv  I though in this one as a sick sinus syndrome hahaha in UW. +
pg32  Pretty sure boards and beyond teaches this wrong. Dr. Ryan says that in euthyroid sick syndrome T3, T4 and TSH will be low, but rT3 will be elevated. +
pathogen7  In reality, TSH and T4 levels can be highly variable based on the stage of Euthyroid sick syndrome. One thing that happens for sure, I believe, is that T3 is down and rT3 is up. +

submitted by eacv(19),

If u are not goot in math like me xD. I did it this way: They gave me p^2=1/900 so p=1/30.

Now I need to find P, so use p+q=1. p= 1-(1/30)= 1-0.03= 0.97

So, 2pq= 2(0.97)(0.03)= 0.064 = (1/15) :D I got it right, this is my way to do it cause im not good at fractions.

eacv  **** q=1/900 +
bdaines8  you literally have a calculator to use.... use it +

eacv  here is a video for ilustration https://www.youtube.com/watch?v=US0vNoxsW-k +2

submitted by usmile1(55),

If you look at Uworld question ID 12299 it has a wonderful explanation for this. If they share the same epitopes, it will have a downward slope. If they share none of the same epitopes, the line will be horizontal across the graph (indicating no change as the amount of Y added increases)

eacv  omg YES!! thanks Uworld I got it correct! exactly this qx asked the exact opposite thing! Hahaha I loved it !! +4
pg32  Even after reading the UWorld explanation, I am still not sure how the answer that reads, "Protein Y expresses all of the epitopes expressed by protein X, but protein X does not..." is incorrect. Based on the graph, I don't see a way we can rule out that answer choice and it sounds more likely than both X and Y having the EXACT SAME epitopes. Can anyone explain? What would the graph look like if the quoted answer choice was correct? +1
69_nbme_420  If you make up an example with numbers, it really helps! â€śProtein Y expresses all of the epitopes expressed by X, but protein X does not express all of epitopes expressed by Protein Y.â€ť If we say protein Y has epitopes 1, 2, and 3. Then Protein X has epitopes 1 and 3. Then we can clearly see the relationship the AMOUNT of Y added relative to X bound would NOT be linear. Stated another way â€“ we need an exponentially more amount of Y to COMPLETELY unbind X and therefore there would not be a one to one depiction in the graph Similar logic applies for the answer choice that states "protein X expresses all of the epitopes expressed by protein Y, but protein Y does not express all of the epitopes expressed by protein X. E.g. If protein Y has epitopes 1 and 2. And protein X has epitopes 1, 2, and 3. Here again, we have satisfied the answer choices condition, and no matter how much we increase protein Y, protein X will still have epitope 3 bound in this case. +2
69_nbme_420  Just to clarify for the first scenario: We have 3 epitopes on Y, and 2 epitopes on X. That means, assuming the epitopes are all present in equal amounts, if I add 300 grams of protein Y to the solution - only 200 grams will bind protein X. AND ONLY 200 grams of protein X can be unbound. Hope the numbers help! +

submitted by beeip(104),

How to differentiate between Norovirus and Rotavirus here? Must be related to the the contagious nature of the illness?

strugglebus  You know itâ€™s Noro because people are vaccinated against Rota at 2,4,6 months. +3
beeip  @strugglebus: I didn't know about the vaccine schedule. Thanks! +
strugglebus  As an addendum, you know itâ€™s not staph aureus b/c that is rapid onset within 4 hours. +1
asapdoc  @Beeip If you go to the vaccines page in first aid it gives you all the high yield vaccinations. I didnt realize to correlate that page to a lot of questions until I got this answer wrong +4
savdaddy  its norovirus b/c it can survive ~2 weeks without a host, which is why we see family members with symptoms 3 days after the initial virus. +
savdaddy  ***after the initial outbreak +
eacv  for me this was a discart qx: 1.Giardia lamblia not showed steatorrhea and it needs medication to go away. 2. Rotavirus normally in unvaccinated kids. 3. Shiguella VERY inflammatory stool test do not show anything 4.S areus is very FAST 2-6 hr after eat the contaminated food. +2
link981  Norovirus is the most common cause of viral gastroenteritis in the USA due to vaccination. + Rotavirus is the most common cause of viral gastroenteritis in the rest of the world. In this question you had to know the most common cause. +1

submitted by hello(184),

Patient in hypovolemic shock - the clues are low BP and COOL skin. Hypovolemic shock is caused by fluid loss.

The patient has decreased preload b/c of fluid loss, i.e. there is decreased blood volume returning to heart --> thus decreased preload.

endochondral   why not dec SVR? +
sup  @endochondral w/ hypovolemic shock you would see increased systemic arterial resistance as arteries will constrict to try and bring BP back up. +
eacv  @endochondral dec SVR it typicaly of septic shock. +

submitted by thomas(-2),

They tell you that the kid has no clavicle. This means the defect is in membranous ossification, NOT endochondral, so the pathology is NOT going to involve the chondro-whatever cells. decreased ALK is consistent with osteoblast defect.

pakimd  isnt increased alk phos consistent with increased osteoblastic activity? +
eacv  @pakimd Yes ! ALK phos is a measure of osteoblast work, if the are not working is LOW as in thix px. +

submitted by lamhtu(68),

Unusual that the patient is a young girl, OTCD is XLR inheritance.

eacv  yes !!!!! that make me doubt and choose the wrong one -.- +
ally123  FA p. 83 +

submitted by andrewk1(9),

This girl has exercise induced asthma. It is not well understood why it happens but the triggers are recognized. Normally when breathing occurs air is taken in by the nose and the nasal passages and turbinates act to remove dust and humidify/warm the air. Logically this makes the air denser Pv=nRT. So when exercising, breathing through the nose is decreased and replaced by more vigorous mouth breathing. This means the air is not humidified and warmed up. The air is less dense and the asthma ensues. The question took this same principle except reversed it by asking what external condition could lead to the asthma and that would be cold dry air.

eacv  oooh thank u !!! I choose wrong, cold air hehhe +