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NBME 22 Answers
A 30-year-old man comes to the physician because of ...
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.
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.