Attenuated familial adenomatous polyposis: An inherited predisposition to colorectal cancer characterized by fewer than 100 adenomatous polyps in the colon and rectum. It is said to be attenuated because there are fewer polyps than in classic familial adenomatous polyposis (FAP).Attenuatedfamilialadenomatouspolyposis:Aninheritedpredispositiontocolorectalcancercharacterizedbyfewerthan100adenomatouspolypsinthecolonandrectum.Itissaidtobeattenuatedbecausetherearefewerpolypsthaninclassicfamilialadenomatouspolyposis(FAP).Peoplewithattenuatedfamilialadenomatouspolyposis(AFAP)alsotendtobeolderatthediagnosisoftheirpolyps(averageageof44years)andcancer(averageageof56years),10to15yearslaterthaninclassicFAP.TherightsideofthecolontendstobeinvolvedinAFAPandrectalinvolvementisrare.AFAPistransmittedinanautosomaldominantmanner.PeoplewithAFAPoftenbelongtofamiliesthatalsohavememberswithclassicFAP.AsinFAP,theremayalsobepolypshigherupintheintestinaltractintheduodenumandstomachandanelevatedriskofstomach,liver,andbreastcancer.AndasinFAP,AFAPisassociatedwithmutationsintheAPCgene(insomecases).APCgenetestingcanthereforebeinformativeinpeoplesuspectedofhavingAFAP.IfAPCtestingisnegative,thengenetictestingforMYHmutations(anotherhereditarycauseofcolorectalcancer)maybewarranted.IthasbeenrecommendedthatAFAPpatientshavecolonoscopyratherthansigmoidoscopybecausetheadenomatouspolypsarepredominantlyright-sidedandbeyondthereachofasigmodoscope.Theroleforandtimingofprophylacticcolectomy(precautionaryremovalofthecolon)inAFAPiscontroversial.Onthemolecularlevel,mutationsintheAPCgeneinFAPandAFAPhavebeenfoundinthreedifferentregionsofthegene:Atthe5'endoftheAPCgene,spanningexons4and5;Withinexon9oftheAPCgene;andAtthe3'endoftheAPCgene.Ithasbeenproposedthatmutationsinregion1areassociatedwithagreatrangeinthenumberofcolorectalpolyps(from2tomorethan500)andwiththepresenceofupperintestinalpolyps;thatmutationsinregion2areassociatedwiththepresenceoffrom1to150colorectalpolyps,butnoupperintestinalpolyps;andthatmutationsinregi