GeneticsYuLuDepartmentofRheumatologyRenJiHospitalAchondroplasiaAchondroplasiavs.Chondroplasia(软骨发育不全)（软骨生成）a-chondro-PlasiaWhatisachondroplasia?Achondroplasiaisageneticdisorderofbonegrowththatisevidentatbirth.Itaffectsaboutoneinevery25,000birthsanditoccursinallracesandinbothsexes.ItsdepictioninancientEgyptianartmakesitoneoftheoldestrecordedbirthdefects.Theworda achondroplasiaisderivedfromGreekandmeanswithout cartilage formation,althoughindividualswithachondroplasiadohavecartilage.Duringfetaldevelopmentandchildhood,cartilagenormallydevelopsintobone,exceptinafewplaces,suchasthenoseandears.Inindividualswithachondroplasia,somethinggoeswrongduringthisprocess,especiallyinthelongbones(suchasthoseoftheupperarmsandthighs).Therateatwhichcartilagecellsinthegrowthplatesofthelongbonesturnintoboneisslow,leadingtoshortbonesandreducedheight.Whatdoesapersonwithachondroplasialooklike?Achildwithachondroplasiahasarelativelynormaltorsoandshortarmsandlegs.Theupperarmsandthighsaremoreshortenedthantheforearmsandlowerlegs.Generally,theheadislarge,theforeheadisprominentandthenoseisflatatthebridge.Sometimes,thelargeheadsizereflectshydrocephalus(excessfluidinthebrain),andrequiresurgery. Handsareshortwithstubbyfingers.Thereisaseparationbetweenthemiddleandringfingers(tridenthand).Mostindividualswithachondroplasiaeventuallyreachanadultheightofabout4feet.Whatcausesachondroplasia?(1)Achondroplasiaiscausedbyanabnormalgenelocatedononeofthechromosome4pair(humanshave23pairsofchromosomes).Insomecases,achildinheritsachondroplasiafromaparentwhoalsohasthecondition.Ifoneparenthastheconditionandtheotherdoesnot,thereisa50percentchancethattheirchildwillbeaffected.Ifbothparentshaveachondroplasia,thereisa50percentchancethatthechildwillinheritthecondition,a25percentchancethatthechildwillnothaveit,anda25percentchancethatthechildwillinheritoneabnormalgenefromeachparentandhavesevereskeletalabnormalitiesthatleadtoearlydeath.Achildwhodoesnotinheritthegenewillbecompletelyfreeofthecondition,andcannotpassitontohisorherownchildren.Whatcausesachondroplasia?(2)Inmorethan80percentofcases,however,achondroplasiaisnotinheritedbutresultsfromanewmutation(change)thatoccurredintheeggorspermcellthatformedtheembryo.Theparentsofchildrenwithachondroplasiaresultingfromnewmutationsareusuallynormal-sized.Typically,theseparentshavenootherchildrenwithachondroplasia,andthechancesoftheirhavingasecondaffectedchildareextremelysmall.Geneticistshaveobservedthatolder-than-averagefathers(age40andolder)aremorelikelytohavechildrenwithachondroplasiaandcertainotherautosomaldominantconditionscausedbynewmutations.Individualswithachondroplasiaresultingfromnewmutationstransmitthedisordertotheirchildrenasdescribedabove.Canachondroplasiabediagnosedbeforebirth? In1994,researchersidentifiedthegenethatcausesachondroplasia.Thisdiscoveryallowedthedevelopmentofhighlyaccurateprenatalteststhatcandiagnoseorruleoutachondroplasia.Thesetestscanbeofferedwhenbothexpectantparentshaveachondroplasia.Insuchcases,thebabyhasaone-in-fourchanceofinheritinganabnormalgenefromeachparentanddevelopingafatalformofachondroplasia.Afterbirth,itgenerallyisdiagnosedbyphysicalexaminationandX-rays.Howisachondroplasiatreated? TherecurrentlyisnowaytonormalizeskeletaldevelopmentofchildrenwiththedisorderCanachondroplasiabeprevented? Thereisnowaytopreventthemajorityofcasesofachondroplasia,sincethesebirthsresultfromtotallyunexpectedgenemutationsinunaffectedparents.Geneticcounselingcanhelpaffectedadultsmakeinformeddecisionsaboutfamilyplanning.Whatresearchisbeingdoneonachondroplasia?Asnotedabove,scientistshaveidentifiedthegene,andtheexactmutation(change)inthegene,thatcausesachondroplasia.Thegeneisoneofafamilyofgenesthatmakesproteinscalledfibroblastgrowthfactorreceptors.Scientistshaverecentlylinkedthesegeneswithseveralskeletaldisorders.Thefibroblastgrowthfactorreceptorgenedictatestheproductionofaproteinthatislocatedonthesurfaceofcellsofdifferenttissuetypes,includingcartilage.Theproteinnormallyrespondstosignalsfromchemicalscalledgrowthfactorswhichstimulatecellgrowthandmaturation.Nowscientistsareinvestigatinghowthefaultyproteinactuallycausesthefeaturesofachondroplasia.Thiseventuallymayleadtoimprovedtreatmentforthisdisorder,aswellasimprovedunderstandingandtreatmentofotherskeletaldisorderscausedbythisfamilyofgenes.MarchofDimesscientistsandotherresearchersalsoareworkingtoidentifythegenesthatcausesomeoftheothermorethan100formsofdisproportionateshortstructure.AdditionalSourcesofInformationForfurtherinformationonsupportgroupsforindividualswithachondroplasiaorotherformsofgrowthdeficiency,contact:LittlePeopleofAmerica(LPA)P.O.Box745Lubbock,TX79408888-LPA-2001HumanGrowthFoundation997GlenCoveAve.GlenHead,NY11545800-451-6434TheMagicFoundationforChildrensGrowthandRelatedAdultDisorders1327N.HarlemAve.OakPark,IL60302708-383-0808TwinsTwinOperation!“WOW!TwoIranianSiameseTwinsaretobeseprataed!TheyareIranian,andthewordSiameseisnotanethnicalmodifieroftheTwins,butadescriptionofthefactthattheyareconnectedatthehead!JennaandBarbarasureareluckytheywerenotstapledtogeth