Sitosterolemia:ARareGeneticDisorderLeadstoInsightintoanImportantPhysiologicalProcess

Sitosterolemia:ARareGeneticEvidenceforRegulationofDietaryCholesterolAbsorptionInterindividualvariationincholesterolabsorptionratesAbsorptionratesaffectedbydietarycholesterollevelsHighdegreeofspecificityforsterolabsorbed,e.g.,cholesterol>>sitosterolGeneticdiseaseinhumans,phytosterolemiaCholesterolexcretedintobilebytheliver,butmechanism/transportersnotidentifiedEvidenceforRegulationofDieHowisCholesterolAbsorbed?Intestinal

cellFFAMicellesBileacidsLiverCholesterolFFAChylomicronsDigestfood

Cholesterylester

CholesterolFFAFreecholesterolBloodLymphatic

channelsVLDLHowisCholesterolAbsorbed?InSterolAbsorptionBosnerMSetal.JLipidRes1999;40:302-308.NumberofSubjects1st2nd3rd4th5th6th7th8th9th10thDecilePercentCholesterolAbsorptionSterolAbsorptionBosnerMSetDietarySterols:NormalPhysiologyDietarySterols:NormalPhysiHOSitosterolHOStigmasterolSterolStructuresHOCholesterolHOCampesterolHOSitosterolHOStigmasterolSterBhattacharyyaAKetal.JClinInvest1974;53:1033-1043.Sitosterolemia,a.k.a.PhytosterolemiaAutosomalrecessive,firstdescribedin1974DiagnosticallyelevatedplasmaphytosterolsRare,<1:1,000,000(~20casesinUS)AssociatedwithprematureatherosclerosisIncreaseddietarysterolabsorptionandfailuretoexcretesterolsintobileNeedGCorHPLCtomakediagnosisBhattacharyyaAKetal.JClinSitosterolemiaBiochemicalabnormalitiesIncreasedplasmaphytosterolsandtheirmetabolitesIncreaseddietarycholesterolandplantsterolabsorptionExpandedbodypoolsofbothsitosterolandcholesterolDecreasedabilitytoexcreteanysterolsintobilebytheliverSitosterolemiaBiochemicalabnoPlasmaSitosterolandCholesterolinSitosterolemiaLeeMHetal.CurrOpinLipidol2001;12:141-149.Cholesterol(mg/dl)PlasmaCholesterolPlasmaSitosterol(mg/dl)PlasmaSitosterol68584838281883210ParentsNormal

SiblingsAffected

IndividualsNormal

ControlsParentsNormal

SiblingsAffected

IndividualsNormal

ControlsPlasmaSitosterolandCholesteSummaryofMetabolicDefectLossofsteroldiscrimination,withReducedbileexcretionofsterolsHyperabsorptionofallsterolsReducedsterolturnoverAbnormalregulationofcholesterolsyntheticpathwayReducedactivitiesofHMG-CoAreductase,synthase,butincreasedLDL-receptoractivitySummaryofMetabolicDefectLosSitosterolandAtherosclerosis:

InsightfromHomozygousSitosterolemiaAutopsystudy

ofyoung

sitosterolemic

patientwhohad

suddendeath~20%plant

sterolcontentof

atherosclerotic

plaqueSameproportionsofsterolsasinLDLSitosterolandAtherosclerosisHypothesisPrimarydefectinvolvesageneproductthatRegulatescholesterolabsorptioninthegutRegulatescholesterolexcretionintheliverPreventsnoncholesterolsterolsfrombeingretainedbythebodyPreventsentryintheintestineAnysmallamountsthatescapetheintestinearerapidlyexcretedbytheliverHypothesisPrimarydefectinvolGeneticAnalysesAssemblepedigrees,confirmdiagnosisbyplasmasitosterollevels,collectDNALow-densitygenomewide-scanperformedInitiallyat25cMresolution10–15cMatconclusionHigh-densitymappinguponlocalizationPositionallyclonethediseasegeneGeneticAnalysesAssemblepedig2200757673747778798081828384858687929324008889230057582000535410002100636462656667686172717069100234561200891011127FamilieswithSitosterolemia13143001516500232425262722600293031323328700363734353839404142474645800434421201940017189697250010010126002700105104103106107108109110111280011211331001241251221233200128129126127300011911812012138001491481471523900151150153154135340013413313613713013133001321381393500140141142360014314414537001464000157158159160155156175440017417317617717017143001721611624100163LeeMHetal.CurrOpinLipidol2001;12:141-149.114290011611511755565960909194959899102220075767374777879808182838485Fine-MappingofSTSLtoD2S2294–D2S2174LeeMHetal.EurJHumGenet2001;9:375-384.?2001NaturePublishingGroup.Allrightsreserved.131197531-1-305101520HaldaneMapPositionMultipointLODScoreD2S1346GATA194B06D2S2259D2S4010D2S2298D2S4015D2S2240D2S2378D2S123D2S2153D2S4009Fine-MappingofSTSLtoD2S229LuKetal.AmJHumGenet2001;69:278-290.?2001TheAmericanSocietyofHumanGenetics.AllRightsReservedGeneStructuresofABCG5(Sterolin-1)andABCG8(Sterolin-2)Centromere1kbABCG8ABCG5TelomereATGATG372bp~143bp121311108976534211Exon1

ABCG8Exon1

ABCG5LuKetal.AmJHumGenet200ExpressionPatternsofABCG5andABCG8inMouseTissueskb6.05.04.03.02.52.01.56.05.04.03.02.52.01.53.02.52.01.5ABCG5ABCG8-actinLeeMHetal.NatGenet2001;27:79-83.|LuKetal.AmJHumGenet2001;69:278-290.?2001NaturePublishingGroup.Allrightsreserved.BrainKidneyLungSkinSpleenTestisHeartLiverMuscleSmall

IntestineStomachThymusExpressionPatternsofABCG5aMutationsinABCG5andABCG8CauseSitosterolemiaMutationsinABCG5andABCG8CWhatareABCProteins?ATP-bindingcassettecontainingmembrane"transporters"Definedby"Walker"motifsAandBSubsequentlya"C"motifdefinedLargefamilyPresentinbacteriatomammals55genesinDrosophilamelanogaster56inCaenorhabditiselegans51inHomosapiens>130inArabidopsisthalianaWhatareABCProteins?ATP-bindABCGenesandHumanDiseaseOncologyChemotherapeuticresistancePulmonologyCysticfibrosisCardiology/metabolicTangierdiseaseSitosterolemiaEndocrinologyNesidioblastosis(PHHI)OphthalmologyStargardt’smaculardystrophyDermatologyPseudoxanthomaelasticumImmunologyAntigenpresentation"Barelymphocyte"HematologyX-linkedsideroblasticanemiaNeurologyAdrenoleukodystrophyHepatologyFamilialcholestasisABCGenesandHumanDiseaseOncMutationsinABCG5(sterolin-1)andABCG8(sterolin-2)causesitosterolemiaAffectedindividualshavehighlevelsofplantsterols,butnotalwayscholesterolTendon/tuberousxanthomasandacceleratedatherosclerosisMustplayakeyroleinregulatingdietarysterolabsorptionandexcretion?LinkbetweendietandatherosclerosisDosterolinspreventtheentryoftoxicbioactivesterols?Conclusions:ABCG5andABCG8MutationsinABCG5(sterolin-1NoncholesterolSterolsEndogenoussterolsSterolsynthesisintermediatesDesmosterolLathosterolCholestenol,etcMetabolitesCholestanolOxysterolsExogenoussterolsPlantsterolsSitosterolCampesterolBrassicasterolAvenosterol,etc.YeaststerolsErgosterol,etc.ShellfishsterolsDesmosterolFucosterol,etc.NoncholesterolSterolsEndogenoElevatedPhytosterolsareaMarkerofCHDHypercholesterolemics

(n=595)Hyperphytosterolemics

(n=21)Sitosterol0.2650.628Campesterol0.1640.594Cholesterol261262SitosterolandcampesterolconcentrationswerehigherinsubjectswithpersonalorfamilyhistoryofprematureCHD42%ofprobands'kindredhadhistoryofprematureCHDversus19%ofthecohort(P=0.13)GlueckCJetal.Metabolism1991;40:842-848.Allvaluesexpressedasmg/dlElevatedPhytosterolsareaMaRajaratnamRAetal.JAmCollCardiol2000;35:1185-1191.SitosterolConcentrationsinPostmenopausalWomenwithCHDPostmenopausalwomenwithCHDhadhigherlevelsofsitosterolandcampesterol;resultsremainedsignificantafteradjustmentforotherriskfactorsDataaremean(SD)Valuesexpressedasmg/dlCases

(n=48)Controls

(n=61)PSitosterol0.332(0.22)0.271(0.13)

<0.05Campesterol0.611(0.44)0.493(0.25)

<0.05Cholesterol

230(5.41)

221(4.64)>0.1RajaratnamRAetal.JAmCollLiverFecalsterolsBilesalts

Unabsorbed

cholesterol

CholBile

saltsBileDuodenal/jejunal

enterocyte

DietLuminal

cholesterolBile

saltsIleal

enterocyte

SterolpermeaseBile

saltsBASMicellar

cholesterolEzetimibeMechanismofIntestinal-ActingAgentsChylomicronLymphChylomicronHepatic

portal

circulationPlantstanolsABCG5/G8IBATSlidedevelopedbyTheHealthScienceCenterforContinuingMedicalEducation,NewYork,NYLiverFecalsterolsBiles