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free120/Block 3/Question#27 (18.1 difficulty score)
A 30-year-old woman comes to the physician ...
The second CFTR mutation was not detected by the testing obtained🔍

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submitted by benwhite_dotcom(465),
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sctyiC riibosfs is an aoltoumsa seisveerc essaide iiongvnvl RFTC wc(hih enescod eth FRTC eitp),onr whcih eanms yuo ndee a lodbue iht to sxseepr hte dseeis.a If eht eecngti tets nyol dpecki up one, etnh ti msut aveh dsmise eth .ohetr

drdoom  The reason something is an “autosomal recessive” disease is because the protein encoded by the gene (of which you have two alleles, remember) does something where as long as you make SOME protein, your body should be okay. That’s kind of vague, so take the case of Cystic Fibrosis: you don’t present with Cystic Fibrosis if you have at least one functional allele -- that’s because CFTR protein is a protein that (in the case of bronchiole tissue) moves Chloride ion from inside cells to the outside lumen, which brings with it H2O and keeps the bronchiole lumen nice and watery, and fluid and non-viscous and non-pluggy. So long as you make enough of this protein, you don’t “need” both alleles to be good; the good allele can “make up for” (make enough of the protein product) to compensate for the “broken allele.” So, once again, understanding the pathophys of a disease allows you to reason through and predict things like disease penetrance and expressivity. +3  

submitted by drdoom(806),
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The arnseo eihomngst is na sauto“mloa ecevsirse” esdiase si sbeuaec het eonrpti ndeceod yb teh nege o(f ichhw you eavh otw lell,eas of sreo)uc esod gsniohmte hreew as lgon as yuo akme EMSO nrp,oite uyro oybd huolsd eb ayk.o

aTsht’ nkdi of evuag, so eatk eht aesc fo scytCi Fi:sosibr uoy ’dotn esntrpe hiwt syCtic iobssirF fi uoy vaeh at stael noe iutanoclfn alleel -- sath’t useabce RFCT inertop is a oepntir ttah ni( het seca fo ochilbeorn ues)tsi veoms Cl- fmor iinesd lselc to eht udtseio nl,meu wchhi sgnrib ihwt it 2HO adn sepke teh hocrielnbo lmenu neci dan ywret,a adn iflud and v-sosoncinu and

So ngol as you ekam eohgun of isth peti,onr uyo n’otd e”end“ bhto lsleela to eb dg;oo het ogod aellel nca m“aek pu ”for a(mke heuong fo hte treipno tduorcp ot peseomctan r)fo eht n“orekb ”lael.el So, ocne a,ngia naugdisnedrtn eth tyophhspa fo a diaeess sllawo uyo ot osaner uhrghot dna crditep sgtnih ikle sisaeed cnteerepan nad t.reivepxyssi

submitted by dixie96(3),

does not need to be the same mutation recall CF has many mutations that cause it so likely this patient has 2 different mutations both of which led to her having CF and the test was specific only for one of her mutations

submitted by melchior(41),

To those wondering how a CFTR mutation is not detected:

CF can result from more than a thousand different mutations.[45] As of 2016, typically only the most common mutations are tested for, such as ΔF508[45] Most commercially available tests look for 32 or fewer different mutations.