Individuals with Klinefelter syndrome tend to have anxiety, depression, impaired social skills, behavioral problems such as emotional immaturity ...YouAreHere:Home→Genetics→GeneticConditions→KlinefeltersyndromeURLofthispage:https://medlineplus.gov/genetics/condition/klinefelter-syndrome/KlinefeltersyndromeFromGeneticsHomeReference.LearnmoreDescriptionKlinefeltersyndromeisachromosomalconditioninboysandmenthatcanaffectphysicalandintellectualdevelopment.Mostcommonly,affectedindividualsaretallerthanaverageareunabletofatherbiologicalchildren(infertile);howeverthesignsandsymptomsofKlinefeltersyndromevaryamongboysandmenwiththiscondition.Insomecases,thefeaturesoftheconditionaresomildthattheconditionisnotdiagnoseduntilpubertyoradulthood,andresearchersbelievethatupto75percentofaffectedmenandboysareneverdiagnosed.BoysandmenwithKlinefeltersyndrometypicallyhavesmalltestesthatproduceareducedamountoftestosterone(primarytesticularinsufficiency).Testosteroneisthehormonethatdirectsmalesexualdevelopmentbeforebirthandduringpuberty.Withouttreatment,theshortageoftestosteronecanleadtodelayedorincompletepuberty,breastenlargement(gynecomastia),decreasedmusclemass,decreasedbonedensity,andareducedamountoffacialandbodyhair.Asaresultofthesmalltestesanddecreasedhormoneproduction,affectedmalesareinfertilebutmaybenefitfromassistedreproductivetechnologies.Someaffectedindividualsalsohavedifferencesintheirgenitalia,includingundescendedtestes(cryptorchidism),theopeningoftheurethraontheundersideofthepenis(hypospadias),oranunusuallysmallpenis(micropenis).OtherphysicalchangesassociatedwithKlinefeltersyndromeareusuallysubtle.Olderchildrenandadultswiththeconditiontendtobesomewhattallerthantheirpeers.Otherdifferencescanincludeabnormalfusionofcertainbonesintheforearm(radioulnarsynostosis),curvedpinkyfingers(fifthfingerclinodactyly),andflatfeet(pesplanus).ChildrenwithKlinefeltersyndromemayhavelowmuscletone(hypotonia)andproblemswithcoordinationthatmaydelaythedevelopmentofmotorskills,suchassitting,standing,andw