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NBME 21 Answers

nbme21/Block 4/Question#20 (56.6 difficulty score)
A 7-month-old boy is brought to the physician ...
46,XYπŸ”
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 +19 
submitted by hungrybox(968),
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ishT viode alepnsxi tglniea ombyrlogey lemyerxte l.elw

If yuo tlef tatloyl ltos ekil ,me twcha hte ideov ftrsi ta x2, nhte cehkc uto eth obtotm rigefu on .gp 680 in AF 192.0

avetlRne ot sthi un:eotisq

  1. SYR rsitpoen liamttesu eoltdpeemvn fo tssete
  2. hsiT pt sah ssetet ;gt=& eh smtu heva eht RYS gnee on het Y mhcomreoso
  3. FIM garedsde eth ilaeluMnr udct, wcihh douwl wesreothi becmoe eht nairnetl fleaem atglniaei
  4. ihsT pt has ailentrn eflaem ntiaglaei ;>= dtdni' kaem egunho FIM

uiQz reyuslof arswe(sn in a rsatpaee otps):

  1. sihT nettas'ip rsiroded acn be rdetca acbk ot hwcih cesl?l
  2. This ptenait adh maolnr nei.gliata If sthi pntaeti had rmlaesl egniaatli ntah m,ronal atth douwl be a fdeetc in wtah zyemne?
ergogenic22  I like to work backwards. 1) patient has normal testicles on histology, normal appearing penis this must mean a Y chromosome is present, as testis determining factor is on the y chromosome (see above post point #2). I.e. you can eliminate choice A and B. Theoretically, 47XY and 47XYY could also present with female genitalia due to lack of MIF, but normal 46XY is more common +11  



 +7 
submitted by hungrybox(968),
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zuqi rlsyefuo ewnss:ra

  1. olitSre r(ieloSt sthSu ,nwod MFI is etceesrd by roeSlit e)llcs
  2. -a5phla sdcteearu
lovebug  5-alpha reductase is due te that DHT is important for male external genitalia? +  



 +5 
submitted by d_holles(171),
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hits si a sslcica tiiodnrcpse fo pnretsiste liuraleMn tucd mynrsode

.ecgloue_p/itMiaulndmsieodrydr_warkni

deu to cakl of MIF atmuo(int in eht eegn atth esmka IFM) β†’ pnsecreiset of eth lnMieluar duct β†’ retuus and lnlfoipaa ubte esrpetn in a XY lmea /w tteses ypylcti(al pcrryoi)hdt.c




 +4 
submitted by drachenx(49),
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seeaBcu hsi itseteslc ear sneedcu,nded ihs rtoseli lcsel rea rybpalob otn kownrig ep,lrpyro and heereoftr not tyisiezhsnng MIF .rcylorect hihcW si ywh shi natnerli flaeme itnlgaiea si lwadloe ot vploedee ni a dtluaef entg.sti




 +3 
submitted by gabstep(14),
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'Im gintinhk htsi is ecdeesdar vlseel of niirteulanM-al nroeo?hm hisT si hawt lysualu tiihbsin eth eoaiphncrmasrpe ctdu mat(lletuyi velsdpeo tnio enntaril efmeal lien)agtai ni al.mse A aiptnet cna eb XY nad lslti heav eceraedds s.ellve

gabstep  FA 2019 pg 608 +  



 +2 
submitted by readit(14),

Addition to Hungrybox's explanation:

Why it's not 47,XXY:

This would be referring to Klinefelter's, which is characterized by small, poorly functioning testicles.

However, question states "morphologic studies of a biopsy specimen of the testes show no abnormalities"

readit  More specifically, in Klinefelter's, you would see "hyaline seminiferous tubules/sertoli cells" on histology +2  
pg32  Thanks! Where did you get the histologic description from? +1