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1、GeneticsYuLuDepartmentofRheumatologyRenJiHospitalAchondroplasiaAchondroplasiavs.Chondroplasia(软骨发育不全)（软骨生成）a-chondro-PlasiaWhatisachondroplasia?Achondroplasiaisageneticdisorderofbonegrowththatisevidentatbirth.Itaffectsaboutoneinevery25,000birthsanditoccursinallracesandinbothsexes.Itsdepictioninancie
2、ntEgyptianartmakesitoneoftheoldestrecordedbirthdefects.Theworda achondroplasiaisderivedfromGreekandmeanswithout cartilage formation,althoughindividualswithachondroplasiadohavecartilage.Duringfetaldevelopmentandchildhood,cartilagenormallydevelopsintobone,exceptinafewplaces,suchasthenoseandears.Inindi
3、vidualswithachondroplasia,somethinggoeswrongduringthisprocess,especiallyinthelongbones(suchasthoseoftheupperarmsandthighs).Therateatwhichcartilagecellsinthegrowthplatesofthelongbonesturnintoboneisslow,leadingtoshortbonesandreducedheight.Whatdoesapersonwithachondroplasialooklike?Achildwithachondropla
4、siahasarelativelynormaltorsoandshortarmsandlegs.Theupperarmsandthighsaremoreshortenedthantheforearmsandlowerlegs.Generally,theheadislarge,theforeheadisprominentandthenoseisflatatthebridge.Sometimes,thelargeheadsizereflectshydrocephalus(excessfluidinthebrain),andrequiresurgery. Handsareshortwithstubb
5、yfingers.Thereisaseparationbetweenthemiddleandringfingers(tridenthand).Mostindividualswithachondroplasiaeventuallyreachanadultheightofabout4feet.Whatcausesachondroplasia?(1)Achondroplasiaiscausedbyanabnormalgenelocatedononeofthechromosome4pair(humanshave23pairsofchromosomes).Insomecases,achildinheri
6、tsachondroplasiafromaparentwhoalsohasthecondition.Ifoneparenthastheconditionandtheotherdoesnot,thereisa50percentchancethattheirchildwillbeaffected.Ifbothparentshaveachondroplasia,thereisa50percentchancethatthechildwillinheritthecondition,a25percentchancethatthechildwillnothaveit,anda25percentchancet
7、hatthechildwillinheritoneabnormalgenefromeachparentandhavesevereskeletalabnormalitiesthatleadtoearlydeath.Achildwhodoesnotinheritthegenewillbecompletelyfreeofthecondition,andcannotpassitontohisorherownchildren.Whatcausesachondroplasia?(2)Inmorethan80percentofcases,however,achondroplasiaisnotinherite
8、dbutresultsfromanewmutation(change)thatoccurredintheeggorspermcellthatformedtheembryo.Theparentsofchildrenwithachondroplasiaresultingfromnewmutationsareusuallynormal-sized.Typically,theseparentshavenootherchildrenwithachondroplasia,andthechancesoftheirhavingasecondaffectedchildareextremelysmall.Gene
9、ticistshaveobservedthatolder-than-averagefathers(age40andolder)aremorelikelytohavechildrenwithachondroplasiaandcertainotherautosomaldominantconditionscausedbynewmutations.Individualswithachondroplasiaresultingfromnewmutationstransmitthedisordertotheirchildrenasdescribedabove.Canachondroplasiabediagn
10、osedbeforebirth? In1994,researchersidentifiedthegenethatcausesachondroplasia.Thisdiscoveryallowedthedevelopmentofhighlyaccurateprenatalteststhatcandiagnoseorruleoutachondroplasia.Thesetestscanbeofferedwhenbothexpectantparentshaveachondroplasia.Insuchcases,thebabyhasaone-in-fourchanceofinheritinganab
11、normalgenefromeachparentanddevelopingafatalformofachondroplasia.Afterbirth,itgenerallyisdiagnosedbyphysicalexaminationandX-rays.Howisachondroplasiatreated? TherecurrentlyisnowaytonormalizeskeletaldevelopmentofchildrenwiththedisorderCanachondroplasiabeprevented? Thereisnowaytopreventthemajorityofcase
12、sofachondroplasia,sincethesebirthsresultfromtotallyunexpectedgenemutationsinunaffectedparents.Geneticcounselingcanhelpaffectedadultsmakeinformeddecisionsaboutfamilyplanning.Whatresearchisbeingdoneonachondroplasia?Asnotedabove,scientistshaveidentifiedthegene,andtheexactmutation(change)inthegene,thatc
13、ausesachondroplasia.Thegeneisoneofafamilyofgenesthatmakesproteinscalledfibroblastgrowthfactorreceptors.Scientistshaverecentlylinkedthesegeneswithseveralskeletaldisorders.Thefibroblastgrowthfactorreceptorgenedictatestheproductionofaproteinthatislocatedonthesurfaceofcellsofdifferenttissuetypes,includi
14、ngcartilage.Theproteinnormallyrespondstosignalsfromchemicalscalledgrowthfactorswhichstimulatecellgrowthandmaturation.Nowscientistsareinvestigatinghowthefaultyproteinactuallycausesthefeaturesofachondroplasia.Thiseventuallymayleadtoimprovedtreatmentforthisdisorder,aswellasimprovedunderstandingandtreat
15、mentofotherskeletaldisorderscausedbythisfamilyofgenes.MarchofDimesscientistsandotherresearchersalsoareworkingtoidentifythegenesthatcausesomeoftheothermorethan100formsofdisproportionateshortstructure.AdditionalSourcesofInformationForfurtherinformationonsupportgroupsforindividualswithachondroplasiaoro
16、therformsofgrowthdeficiency,contact:LittlePeopleofAmerica(LPA)P.O.Box745Lubbock,TX79408888-LPA-2001HumanGrowthFoundation997GlenCoveAve.GlenHead,NY11545800-451-6434TheMagicFoundationforChildrensGrowthandRelatedAdultDisorders1327N.HarlemAve.OakPark,IL60302708-383-0808TwinsTwinOperation!“WOW!TwoIranianSiameseTwinsaretobeseprataed!TheyareIranian,andthewordSiameseisnotanethnicalmodifieroftheTwins,butadescriptionofthefactthattheyareconnectedatthehead!JennaandBarbarasureareluckytheywerenotstapledtogeth
