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LETTERTOTHEEDITOROpenAccessDesmosterolosis:anillustrationofdiagnosticambiguityofcholesterolsynthesisdisordersCristinaDias1,2,6,RosemarieRupps1,2,BenjaminMillar1,KunhoChoi2,MarcoMarra1,3,MichelleDemos4,LisaEKratz5andCorneliusFBoerkoel1,2*AbstractDesmosterolosisisanautosomalrecessivedisorderofcholesterolbiosynthesiscausedbybiallelicmutationsofDHCR24(homozygousorcompoundheterozygous),whichencodes3-β-hydroxysterolΔ-24-reductase.
Wereporttwosistershomozygousforthe571G>A(E191K)DHCR24mutation.
Comparisonofthepropositaetootherreportedindividualsshowsthatpsychomotordevelopmentaldelay,failuretothrive,dysgenesisofthecorpuscallosum,cerebralwhitematteratrophyandspasticitylikelyconstitutetheminimaldesmosterolosisphenotype.
Thenonspecificfeaturesofdesmosterolosismakeitdifficulttosuspectclinicallyandthereforescreeningforitshouldbeentertainedearlyinthediagnosticevaluation.
Keywords:DHCR24,Desmosterol,Intellectualdisability,Cholesterolbiosynthesis,ExomesequencingFindingsBackgroundDesmosterolosisisaninfrequentlyreporteddisorderofcholesterolbiosynthesiscausingsyndromicintellectualdisability(ID)arisingfrombiallelicmutations(homozy-gousorcompoundheterozygous)inDHCR24.
DHCR24encodes3-β-hydroxysterolΔ-24-reductase(DHCR24)[1,2],whichcatalyzestheC-24NADPH-dependentre-ductionofthe24–25doublebondofcholesterolprecur-sors[3,4].
CasereportWepresenttwosisterswithsyndromicIDanddesmos-terolosis.
Followinguncomplicatedpregnancies,theywerebornattermwithnormalgrowthparameters.
Eachhadtransientneonatalseizures.
Theirfamilyhistorywasnoncontributory.
Beginningininfancy,theymanifestedgrowthrestric-tionanddelayedmilestonesforspeech,fineandgrossmotor,andadaptivedevelopment.
Patient1wasabletowalkwithsupportandcommunicatewithshortphrasesby6years;Patient2developedtheseskillsby8years.
Patient1hadanIQof42at10.
5years.
Patient2hadanIQof46at5.
5years.
NeitherlostskillsalthoughPatient1hadprogressivesensorineuralhearingloss.
Onexaminationat13.
8and9.
1years,respectively,eachhadsimilardysmorphicfeatures.
Patient1hadshortstature(97thcentile).
Pa-tient2alsohadmyopia.
InvestigationsEachhadextensivenon-diagnosticlaboratorytesting.
Thisincludednormalprofilesforurineorganicacids,urinepurinesandpyrimidines,plasmaaminoacids,andplasmaverylongchainfattyacidsaswellasurine*Correspondence:nboerkoel@cfri.
caEqualcontributors1DepartmentofMedicalGenetics,UniversityofBritishColumbia,4500OakSt.
,Vancouver,BritishColumbia,V6H3N1,Canada2ChildandFamilyResearchInstitute,Children'sandWomen'sHealthCentreofBritishColumbia,950West28thAve.
,Vancouver,BritishColumbia,V5Z4H4,CanadaFulllistofauthorinformationisavailableattheendofthearticle2014Diasetal.
;licenseeBioMedCentralLtd.
ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommonsAttributionLicense(http://creativecommons.
org/licenses/by/4.
0),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycredited.
TheCreativeCommonsPublicDomainDedicationwaiver(http://creativecommons.
org/publicdomain/zero/1.
0/)appliestothedatamadeavailableinthisarticle,unlessotherwisestated.
Diasetal.
OrphanetJournalofRareDiseases2014,9:94http://www.
ojrd.
com/content/9/1/94mucopolysaccharideandoligosaccharidescreens,liverfunctionstudies,transferrinisoelectricfocusingandlevelsforlactate,ammonia,uricacid,albumin,creatininephos-phokinase,andthyroidstimulatinghormone.
Eachhadanormalkaryotypeandnoevidenceofagenomicdeletionorduplicationdetectablebyarraycomparativegenomichybridization.
Patient1alsohadnormalnucleotideexci-sionrepairassays,electromyographyandnerveconduc-tionstudies.
Patient2hadnormalcompletebloodcountsandlevelsforcopper,ceruloplasminandbloodacylcarni-tines;herEEGidentifiednofocalseizureactivity.
Thepatientswereunavailableforadditionaltesting,specif-icallyplasmasterols,whichwerenotperformedoninitialassessment.
Radiologicalassessmentshowedthatbothhaddislo-catedradialheadsandbilateralequinovarus.
Inaddition,Patient1hadasmallanddeformedpelvis,lumbarscoli-osis,andmoderateosteopenia.
Patient2hadparietalforamina.
Magneticresonanceimaging(MRI)identifiedmildbrainatrophy,asymmetricventriculomegaly,athincorpuscal-losum,andaChiariImalformation(Figure1D,E,IandJ)Inaddition,Patient1hadasacralcystsuggestiveofameningoceleordural/perineuralcyst.
ExomesequencingandbiochemicalconfirmationofdesmosterolosisExomesequencing(formethodsseeAdditionalfile1)[5]identifiedahomozygousDHCR24mutation(NM_014762.
3:c.
571G>A;p.
E191K),arecognizedcauseofdesmosterolosis(Additionalfile1,SupplementarymethodsandAdditionalfile2:FigureS1A)[2].
Sangersequencingconfirmedthisandthecarrierstateoftheparents(Additionalfile2:FigureS1B).
Aspredicted,gaschromatography-massspectroscopyanalysisoflysatesfromculturedlympho-blastoidcells[6]fromthepropositaedetectedanin-creasedratioofdesmosteroltototalsterols(Figure2).
Allothersterolsmeasured(Supplementarymethods)includ-ingcholesteroland7-dehydrocholesterolwerewithinnor-malrangecomparedtohealthycontrols.
ConclusionsWepresenttwosisterswiththebiallelicmutationNM_014762.
3:c.
571G>AinDHCR24.
Therecurrenceofthismutation[2]inadifferentethnicgroupimpliesthatthismutationaroseindependentlyandsuggeststhatmu-tationsalteringonlycertainaminoacidsgiverisetoavi-ablehumanwithdesmosterolosis(Table1).
Figure1ClinicalandMRIfeaturesofsiblingswithDesmosterolosis.
AtoC:Patient1craniofacialandhandfeaturesatage14.
8years.
Herdysmorphicfeaturesshowscaphocephaly,tallforeheadwithbitemporalnarrowing,shortpalpebralfissures,longnose,hypoplasticnasalalae,prominentcolumella,andlow-setposteriorlyrotatedears.
D,E(AxialT1,SagittalFLAIR):Patient1brainMRIshowingwhitemattervolumeloss,dilatedventricles,thincorpuscallosum,andpeg-likecerebellartonsilsdisplacedintotheuppercervicalcanalthroughtheforamenmagnum(ChiariImalformation).
FtoH:Patient2craniofacialandhandfeaturesatage10.
1years,similartoPatient1.
I,J(AxialT1andSagittalFLAIR):Patient2brainMRIshowingprominentandirregularventricles,thincorpuscallosum,andChiariImalformation.
Diasetal.
OrphanetJournalofRareDiseases2014,9:94Page2of6http://www.
ojrd.
com/content/9/1/94Assessinggenotype-phenotypecorrelation,thepropo-sitaewerediscordantformicroretrognathia,cleftpalate,largejointcontractures,deafness,andskullforamina(Table1).
Incontrast,thepreviouslyreportedfourcousinsofaconsanguineousfamilywerediscordantforoculo-motorabnormalitiesandseizures(Patients4–7,Table1).
Thismightsuggesteitherthatthegeneticbackgroundsofthepropositaearesignificantlydifferentorthatbecauseoftheirconsanguinity,thefourfamilymembersreportedbyZolotushkoetal.
[7]shareothergenomicorepigeneticvariantsmodifyingtheexpressivityofdesmosterolosis.
ComparisonofthepropositaetoPatient3(Table1),whohasthesameDHCR24mutation,providesanas-sessmentofinterfamilialgenotype-phenotypeconcord-ance[2].
Theywerediscordantfordysmorphicfacialfeatures,oculomotorabnormalities,seizures,brainventri-culomegaly,cutisaplasia,limbanomalies,andcongenitalheartdefects.
TheywereconcordantforID,failuretothrive,shortstature,spasticity,distalarthrogryposis,dys-genesisofthecorpuscallosum,andcerebralwhitematteratrophy.
Comparisonofthepropositaetoallreportedinindividualswithdesmosterolosis(Table1)[1,2,7-9]identi-fiesID,failuretothrive,spasticity,dysgenesisofthecor-puscallosum,andcerebralwhitematteratrophyastheminimalclinicalphenotypefordesmosterolosis.
Distalarthrogryposisoccurredin8of9individuals(Table1).
Thisminimalphenotype,whichisnotdistinctiveandtheabsenceofsteroltesting,explainsthedecade-longdiag-nosticodysseyofthepropositae.
Reviewofallreportedpatientssuggestsaminimalgenotype-phenotypecorrelationfordesmosterolosis.
Onlyindividualswithmutationsaffectingthe3-β-hydroxysterolΔ-24-reductasecytoplasmicdomainhadrhizomelia(Patients8and9,Table1).
Sharingthisfeaturewiththeknockoutmice[10],mightsuggestthatmuta-tionsinthecytoplasmicdomaindisruptenzymefunctionmoreseverelythanmutationsintheFAD-bindingdomain(proteinfeaturesofUniProtQ15392[11]).
Theneurologicalfeaturesofdesmosterolosismightarisefromeitherdeficiencyofcholesterolbiosynthesisorthetoxiceffectsofsterolsaccumulatingupstreamof3-β-hydroxysterolΔ-24-reductase.
Bothmechanismscontributetootherdisordersofcholesterolbiosynthesisandthuslikelyapplyhere[12].
Thenon-progressiveneuro-pathologyindesmosterolosisisinkeepingwiththepri-maryimpactoccurringduringbraindevelopment.
Insummary,thepleiotropyandnonspecificityofdes-mosterolosisexplainthelongdiagnosticodysseyofthepropositae.
Also,findingsofdevelopmentaldelay,CNSmalformation,spasticity(withorwithoutdistalarthro-gryposis),shortstaturewithandwithoutlimbanomaliesaresufficientindicationtoscreenfordisordersofchol-esterolbiosynthesis.
PatientconsentandethicsapprovalIndividualsenrolledinthestudygaveinformedconsentforprotocolH07-02142(Vancouver,BC,Canada),ap-provedbytheUniversityofBritishColumbiaResearch051015202530ControlPatient1Patient2MotherFather%Desmosterol%7-DHC%/TotalsterolsFigure2Biochemicalconfirmationofdesmosterolosis.
Comparativesterolprofilesforthepatients(secondandthirdbarsets),heterozygousparents(fourthandfifthbarsets),andunaffectedcontrol(firstbarset).
Sterolsweremeasuredinlysatesfromlymphoblastsculturedindelipidatedmediumfor3daysandshoweda17–25foldincreasedratioofdesmosteroltototalsterolsincomparisontocontrols,whereasasheterozygousparentspresenta1.
7and1.
5increase,respectively.
Eachbarrepresentstheaverageof3technicalreplicates.
7-DHCisrepresentedasaninternalcontrol.
Diasetal.
OrphanetJournalofRareDiseases2014,9:94Page3of6http://www.
ojrd.
com/content/9/1/94Table1ClinicalfeaturesofreportedpatientswithDesmosterolosisFeaturePresentfamilyPreviouslyreportedcasesofdesmosterolosisFrequency(n=9)Patient1Patient2Patient31Patients4-72Patient83Patient94Mutationc.
[571G>A]+[571G>A]p.
[E191K]+[E191K]c.
[571G>A]+[571G>A]p.
[E191K]+[E191K]c.
[307C>T]+[307C>T]p.
[R103C]+[R103C]c.
[281G>A]+[1438G>A]p.
[R94H]+[E480K]c.
[1412A>C]+[881A>C;918G>C]p.
[Y471S]+[N294T;K306N]ProteindomainFAD-bindingdomainFAD-bindingdomainFAD-bindingdomainFAD-bindingdomain+CterminalcytoplasmicdomainCterminalcytoplasmicdomainAncestryMiddleEasternEuropeanIsraeliBedouinEuropeanFailuretothrive1114/41n.
a.
8/8Shortstature111n.
a.
n.
a.
03/4Microcephaly0014/4005/9Macrocephaly0000/4112/9Microretrognatia1014/4118/9Cleftpalate1010013/9FacialfeaturesDolicocephaly;bitemporalnarrowing;lowsetears;shortdownslantingPF;prominentcolumella;cleftpalateDolicocephaly;bitemporalnarrowing;lowsetears;shortdownslantingPF;prominentcolumella;DownslantingPF;bilateralepicanthalfoldsProminentforehead;Shortnose;antevertednares;telecanthus;Frontalbossing;hypoplasticnose;lowsetears;cleftpalateID/DD1114/41n.
a.
8/8Spasticity1114/4n.
a.
n.
a.
7/7Distalarthrogryposis1114/4108/9Largejointcontractures01(talipes)1(talipes)n.
a.
114/5Shorteningofthelimbs000n.
a.
112/5ACC(partial/full)1114/4119/9Ventriculomegaly1104/4118/9CerebralWMatrophy1114/41n.
a.
8/8CerebellarWMatrophy11n.
a.
2/2n.
a.
n.
a.
4/4Nystagmus/strabismus1103/40n.
a.
5/8Seizures1103/4n.
a.
n.
a.
5/7Diasetal.
OrphanetJournalofRareDiseases2014,9:94Page4of6http://www.
ojrd.
com/content/9/1/94Table1ClinicalfeaturesofreportedpatientswithDesmosterolosis(Continued)OtherfeaturesSNHL;HirsutismParietalforamina.
HirsutismCutisaplasia;Limbanomalies;PDA;HydrocephalusOsteosclerosis;ambiguousgenitalia;anomalouspulmonaryvenousdrainage;renalhypoplasia;deathat1hFunctionalassaysExpressedbothmutationsinc.
cerevisiae(separately)withsignificantenzymeactivityExpressedmutationsinc.
cerevisiaewithsignificantenzymeactivity(includingcompoundhet)References:1:Waterhametal.
[2],Anderssonetal.
[8];2:Zolotushkoetal.
[7];3:Schaafetal.
[9];4:FitzPatricketal.
[1],Waterhametal.
[2].
Abbreviations:ACCagenesisofthecorpuscallosum,DDdevelopmentaldelay,IDintellectualdisability,n.
a.
notavailable,PFpalpebralfissures,PDApatentductusarteriosus,SNHLsensorineuralhearingloss,WMwhitematter,hhour,hetheterozygote.
Diasetal.
OrphanetJournalofRareDiseases2014,9:94Page5of6http://www.
ojrd.
com/content/9/1/94EthicsBoard.
Writteninformedconsentwasprovidedforthecollectionofsamples,subsequentanalysisanduseofphotographsbytheparentsofthechildren.
AdditionalfilesAdditionalfile1:Supplementarymethods.
ExomesequencingandGaschromatography-massspectroscopyanalysis.
Additionalfile2:FigureS1.
MolecularconfirmationofDesmosterolosisthroughexomesequencingandSangersequencing.
NextGene(Softgenetics,Pennsylvania)viewoftheexomesequencingreadsforoneaffectedchild(A)anddideoxynucleotidesequencingvalidation(B)forthemother,father,andbothaffectedchildren.
ThemotherandfatherwereheterozygousforNM_014762.
3:c.
571G>A(p.
E191K)mutation.
Thepropositaehavethemutationinhomozygosity.
Abbreviationsbp:basepair;CNS:Centralnervoussystem;IQ:Intelligencequotient;DHCR24:3-β-hydroxysterolΔ-24-reductase;EBP:Emopamilbindingprotein;FISH:Fluorescenceinsituhybridization;ID:Intellectualdisability;MRI:Magneticresonanceimaging;7-DHC:7-dehidrocholesterol;PE:Paired-end.
CompetinginterestsTheauthorsdeclarethattheyhavenocompetinginterests.
Authors'contributionsCD,RRandCFBinterpretedthedataanddraftedandrevisedthemanuscript.
CD,BM,KCandLEKperformedexperimentalworkandinterpretedthedata.
CFB,MDandRRprovidedclinicaldata.
CDandMMperformedandinterpretedthebioinformaticanalysis.
Allauthorsreadandapprovedthefinalmanuscript.
AcknowledgementWethankthefamilyfortheirgenerousparticipationandDr.
RuiF.
Santosforinterpretationoftheradiologicaldata.
ThisworkwassupportedinpartbytheRareDiseaseFoundation.
CDwassupportedbytheCanadianChildHealthClinicianScientistProgramandtheChildandFamilyResearchInstitute.
Authordetails1DepartmentofMedicalGenetics,UniversityofBritishColumbia,4500OakSt.
,Vancouver,BritishColumbia,V6H3N1,Canada.
2ChildandFamilyResearchInstitute,Children'sandWomen'sHealthCentreofBritishColumbia,950West28thAve.
,Vancouver,BritishColumbia,V5Z4H4,Canada.
3Canada'sMichaelSmithGenomeSciencesCentre,570W7thAve,#100,Vancouver,BritishColumbia,V5Z4S6,Canada.
4DivisionofPediatricNeurology,DepartmentofPediatrics,UniversityofBritishColumbia,Vancouver,4480OakStreet,Vancouver,BritishColumbia,V6H3V4,Canada.
5DepartmentofNeurogenetics,KennedyKriegerInstitute,707N.
Broadway,Baltimore,MarylandMD21205,USA.
6WellcomeTrustSangerInstitute,Hinxton,Cambridge,UK.
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doi:10.
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