Klinefelter syndrome is a genetic condition in which a boy is born with an extra X chromosome. Instead of the typical XY chromosomes in men, ...MedicalReferenceFeaturesNewsArchiveNewsReferenceSlideshowsQuizzesVideosQuestions&AnswersSubscribetoNewslettersDietandFitnessSexHealthConcernsLookYourBestEnlargedProstateErectileDysfunctionFlatAbsExercisesHairLossManageYourMigraineProstateCancerSexualConditionsStrengthTrainingMoreRelatedTopicsMen'sHealthReferenceReviewedbyDanBrennan, MDonOctober05,2019InthisArticleWhatIsKlinefelterSyndrome?WhatCausesKlinefelterSyndrome?SymptomsofKlinefelterSyndromeKlinefelterSyndromeDiagnosisTreatmentofKlinefelterSyndromeComplicationsofKlinefelterSyndromePrognosisforKlinefelterSyndromeWhatIsKlinefelterSyndrome?KlinefeltersyndromeisageneticconditioninwhichaboyisbornwithanextraXchromosome.InsteadofthetypicalXYchromosomesinmen,theyhaveXXY,sothisconditionissometimescalledXXYsyndrome.MenwithKlinefelterusuallydon’tknowtheyhaveituntiltheyrunintoproblemstryingtohaveachild.There’snocure,butitcanbetreated.WhatCausesKlinefelterSyndrome?YougettheextraXchromosomebychance.Eithertheeggor thesperm thatcametogethertocreateyouhadanextraXchromosome.OlderwomenhaveaslightlyhigherchanceofhavingaboywithXXYsyndrome,butthechanceissmall.MenwithKlinefeltermayhave:AnextraXchromosomeineverycell,whichisthemostcommonAnextraXchromosomeinonlysomecells,calledmosaicKlinefelter,inwhichyoudon’thaveasmanysymptomsMorethanoneextraXchromosome,whichisveryrareandmoresevereSymptomsofKlinefelterSyndromeSomemenshowsymptomsofKlinefelteraschildren,butothersdon’tknowtheyhaveituntilpubertyoradulthood.Manymenneverrealizethattheyhaveitbecausesymptomsaren’talwayspresent.SymptomsofKlinefeltervarywithageandinclude:Babies: HerniaMorequietthanusualSlowertolearntositup,crawl,andtalkTesticlesthathaven’tdroppedintothescrotumWeakermusclesChildren: AhardtimemakingfriendsandtalkingaboutfeelingsLowenergylevelsProblemslearningtoread,write,anddomathShynessandlowconfidenceTeenagers: Larger breasts thannormal