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Retired NBME 18 Answers

nbme18/Block 2/Question#32 (reveal difficulty score)
A 32-year-old man with an X-linked recessive ...
Type IV collagen ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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submitted by โˆ—azibird(279)
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This really sounds like it's describing Alport syndrome, but Alport syndrome is X-linked DOMINANT! What is going on here? Is this a mistake? How to explain calling it X-linked RECESSIVE?

Alport Syndrome Mutation in type IV collagen -> thinning and splitting of glomerular basement membrane. Most commonly X-linked dominant. Eye problems (eg, retinopathy, anterior lenticonus), glomerulonephritis, sensorineural deafness; โ€œcanโ€™t see, canโ€™t pee, canโ€™t hear a bee.โ€ EMโ€”โ€œbasket-weaveโ€ appearance due to irregular thickening of GBM

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cneal46  lolll apparently 15% of cases are inherited x-recessive. I just ignored the inheritance part and answered based on the functions of all those proteins +1
doublethinker  According to the rare diseases government website, it's OFTEN X-linked recessive: "Alport syndrome can be inherited in three different ways. About 80 percent of cases are caused by mutations in the COL4A5 gene and are inherited in an X-linked recessive pattern." Question def threw me off tho, because I was continuously thinking it's X-linked dominant... https://rarediseases.info.nih.gov/diseases/5785/alport-syndrome +1
epiglotitties  Also, FA 2020 p.581 says "most commonly X-linked dominant" which implies that it has other modes of inheritance +



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