TheMolecular Basis ofPartial Penetrance ofSplicing Mutations in Cystic Fibrosis

Summary Thesplicing variant, 5Tallele, inintron 8ofthecystic fibrosis transmembrane conductance regulator (CFTR) gene wasshown tobeassociated withpartial penetrance oftheclinical expression. Thissplicing variant leads totwopossible transcripts: onenormal andtheother aberrantly spliced that lacks exon9.Theaimofthis study wastoanalyze themolecular basis ofthepartial penetrance inindividuals carrying the5Tallele. Weanalyzed thelevel ofthecorrectly spliced RNA transcribed fromthe5Tallele innasal andepididymal epithelium andcorrelated itwithdisease expression. Semiquantitative nondifferential reverse-transcriptase-PCR showed aconsiderable variability (6%-37%) inthetotal level ofcorrectly spliced RNAtranscribed fromthe5Tallele innasal epithelium from11patients. Asignificant nonlinear correlation (r= .82, P= .002) between thelevel ofthenormal CFTRtranscripts andtheseverity oflung disease wasshown. No individuals withnormal lung function andminimal ornolung disease (FEV1 >80% predicted) had 80%.Thelevel ofnormal transcripts inepididymalepithelial cells fromfour infertile males withcongenital bilateral absence ofthevasdeferens waslow (6%-24%). Ininfertile males with normal lung function thelevel ofcorrectly spliced transcripts inthenasal epithelium washigher than thelevel intheepididymal epithelium. These results indicate that there isvariability in theefficiency ofthesplicing mechanism, amongdifferent individuals andbetween different organs ofthesame individual. This variability provides themolecular basis ofthepartial penetrance ofcystic fibrosis disease inpatients carrying theSTallele.