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 +1  (nbme21#15)

@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





Subcomments ...

submitted by magrufnis(1),

I’m confused about this one. Weakness of extension and pronation of the right forearm, with a decreased triceps muscle stretch reflex. The answer was C7 nerve root, but how are you able to localize to C7 and not C6 or C8? I figured that extension is radial, C5-T1, and pronation is median, also C5-T1. Triceps reflex is C7-C8 (FA2019 says C6-C7). How would you narrow down to just C7 damage?

txallymcbeal  My FA2018 has “C7” bolded, meaning it is the main nerve root. But I also got this one wrong so I can’t be much help besides that. +  
mnemonia  Honestly just a guess but I have this vague understanding that intrinsic hand muscles are C8-T1 so we might’ve expected more hand motor findings as well with a C8 lesion. +1  
theecohummer  I narrowed it down to C7 using the fact that the C7 myotome is elbow extension. I also learned that the C7 nerve root was the main contributor to the triceps DTR so I just went with that. +  
mchu21  They also mentioned that the person had weakness pronating the right forearm which is performed by the biceps. Biceps is innervated by the musculocutaneous nerve which is C5-C7 and that's what helped me pick C7 > C8. +  
mcl  Sorry, I thought the biceps was a supinator of the forearm? +1  
henoch280  yes.. its the supinator not pronator +  


submitted by welpdedelp(74),

So I think that issue of wrist extension and/or finger drop would be more radial nerve. However, there was more proximal weakness, so it would be C7.

"7-8 lay them straight", the pt couldn't "lay them straight" so it would be C7 root

welpdedelp  *As an addition, median nerve involvement would have leaned more toward C8 than C7. +1  
meningitis  Do you have anymore useful mnemonics for brachial plexus? +  
henoch280  FA pg 494 for mnemonics +  


submitted by nwinkelmann(88),

This article explains the pathophysiology well: https://www.ncbi.nlm.nih.gov/books/NBK431048/.

The right ventricle is primarily supplied by the RCA which also supplies the SA node and AV node (90% of hearts because they are right dominant), leading to loss of contractility of the right side, and thus fluid buildup causing elevated central venous pressure. Elevated pressures in the liver and portal system would lead to hepatomegaly and free fluid accumulation in the peritoneum.

henoch280  Hellppp. pls why is it not decreased capillary oncotic pressure? +  
whoissaad  @ henoch280 Because there is no change in the levels of protein in the blood. +  


submitted by dragon3(4),

What's the difference between reactive granulocytosis vs lymphocytosis?

whossayin  Yes I’m at a loss for this one too. Still can’t figure out how we’re expected to differentiate those based on this slide shown. The only logical explanation that I can think of is that reactive lymphocytes may be seen in LYMPHOMAS as opposed to granulocytes which are seen in LEUKEMIAS Such a shitty way to trick us, hah! +  
henoch280  reactive lymphocytes are seen in EBV infection. you would see lymphocytes in the slide not neutrophils FA2018 pg 165 +3  
whossayin  That makes sense.. but was the question talking about EBV infections or hematological malignancies? Just a vague question I wasn’t really sure what exactly was it trying to teach us, I guess the reactive lymphocytosis just threw me off! Anyways, thanks for the clarification buddy! +  
ratadecalle  They way I thought about it was: Granulocytes: multi lobed nucleus Lymphocytes: single lobe +2  
hello  @whossayin - it's not reactive lymphocytosis because there are no buzzword type symtoms of EBV in the Q stem. Also, reactive lymphocytes look way different. +  


submitted by cantaloupe5(35),

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.

temmy  i don't understand this at all. i am completely blank...please help +1  
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 +7  
eacv  @henoch280 thank u very much! I got it right by luck but now i do understand :D +  


submitted by temmy(24),

Healthy people who get sick with parvovirus may have a subclinical illness with athralgias as the only symptom. But sickle cell patients and patients with decreases hematopoiesis will develop[ bone marrow failure because the virus affect the hematopoietic stem cells leading to aplastic crises and inability for the bone marrow to adequately compensate hence the low reticulocyte count. parvovirus causes..slapped cheeks in kids hydrops fetalis in fetus, aplastic crises in sickle cell and arthralgias in other patients.

henoch280  thanks. very helpful +