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NBME 22 Answers

nbme22/Block 1/Question#21

A 30-year-old man comes to the physician because of ...


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1) ADPKD = polycystins (PC2)

2) ARPKD = fibrocystin /polyductin (FPC) -- similar to polycystins

FPC protein is found on the primary cilia of epithelia cells of cortical and medullary collecting ducts and cholangiocytes of bile ducts

FPC interacts with ADPKD protein PC2 and may also participate in this regulation pathway of the mechanosensory function of the primary cilia, calcium signaling, and PCP.

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submitted by dr.xx(45),

The most common and severe form of autosomal dominant polycystic kidney disease (ADPKD) results from mutations in PKD1, encoding polycystin-1 (PC1)..


yotsubato  Here we thank FA for failing us yet again. Giving us PKD1, but not polycystin. I got the question right but I just guessed it because nothing else made sense. +4  
usmleuser007  Autosomal dominant polycystic kidney disease 1) occurs in patients with mutations in the gene (PKD1) encoding polycystin-1 (PC1). 2) PC1 is a complex polytopic membrane protein expressed in cilia that undergoes autoproteolytic cleavage at a G protein–coupled receptor proteolytic site (GPS). 3) A quarter of PKD1 mutations are missense variants, though it is not clear how these mutations promote disease. 4) GPS cleavage is required for PC1 trafficking to cilia. 5) A common feature among a subset of pathogenic missense mutations is a resulting failure of PC1 to traffic to cilia regardless of GPS cleavage. 6) Missense mutation in the gene encoding polycystin-2 (PC2) that prevented this protein from properly trafficking to cilia.  +2  

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submitted by sirminalot(-49),