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free120/Block 3/Question#27 (13.7 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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 +2  upvote downvote
submitted by drdoom(647),
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The eaonsr thmngsoie si an oota“umlsa csvieeers” seeiasd si eeabusc hte tonpire doenedc yb teh neeg (of chihw you aehv otw eslela,l of erosuc) esod ghetionsm hewre sa ongl sa you amke SEMO roitn,pe rouy dboy udshol eb kyo.a

htsaT’ knid fo gu,vea so atke hte caes of ctyCis soFbirsi: yuo d’otn nespetr tihw ycitsC isorbsFi fi you have at tlsea one ounialtnfc aleell -- ts’tha ebecsua CRFT tpiroen is a riopnet hatt (in teh aces fo cbrlooinhe sus)iet vemos C-l form ideins sclle ot hte suioted me,nlu whcih gbrnis thwi ti O2H and peeks the hobioenrlc numle cien dna a,tewry and dluif dan svno-cnsiou nda ulpgyno.-ng

oS nolg as ouy ekam oguehn fo ihst ntroie,p ouy tod’n e“edn” htob leellsa to be ogdo; the gdoo eealll nac ma“ek pu or”f kam(e hegnuo fo hte teporin drtcupo to nescoapetm )rfo the kr“nboe ”elalel. S,o noce angia, ndnargisdteun hte phoyahtps of a eesiasd loswla oyu to enraso thgrohu dna ireptdc shtnig ilke sedsaei reapcnente nad pexei.vsrstiy

 +1  upvote downvote
submitted by melchior(16),

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.


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iCtcys issbfrio is an stloaoamu eesviesrc seadies novlinigv FCTR w(hcih conedse eth FRCT oin)pe,tr ihhcw enasm you eend a uebldo iht ot exrspse eht d.assiee If the gteenci etts lnoy ipcdek up n,oe htne ti sumt vhae edssim the oerht.

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. +2  

 +0  upvote downvote
submitted by dixie96(0),

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