minutesvpsmm

CASEREPORTOpenAccessFirstcasereportofCohensyndromeintheTunisianpopulationcausedbyVPS13BmutationsImenRejeb1*,HouweydaJilani1,YasminaElaribi1,SyrineHizem1,LamiaHila2,JuliaLauerZillahrdt3,4,5,JamelChelly3,4,5andLamiaBenjemaa1AbstractBackground:Cohensyndromeisarareautosomalrecessivedevelopmentaldisorderthatcomprisesvariableclinicalfeaturescountingdevelopmentaldelay,pigmentaryretinopathy,myopia,acquiredmicrocephaly,truncalobesity,jointhypermobility,friendlydispositionandintermittentneutropenia.
VPS13B(vacuolarproteinsorting13,yeast,homologueofB)geneistheonlygeneresponsibleforCohenSyndrome,causativemutationsincludenonsense,missense,indelandsplice-sitevariants.
TheintegrityoftheGolgiapparatusrequiresthepresenceoftheperipheralmembraneproteinVPS13Bthathaveanessentialfunctioninintracellularproteintransportandvesicle-mediatedsorting.
Casepresentation:Inthisstudy,weperformedwholeexomesequencing(WES)inaTunisianfamilywithtwoyoungcaseshavingdevelopmentaldelay,hypotonia,autismspectrumdisorder,ptosisandthickhairandeyebrows.
Thepropositapresentedalsopigmentoryretinopathy.
CompoundheterozygousmutationinVPS13BgenewasdetectedbyWES.
Thismutationinheritedfromhealthyheterozygousparents,supportsanunpredictableclinicaldiagnosisofCohenSyndrome.
Theproband'sphenotypeisexplainedbythepresenceofcompoundheterozygousmutationsintheVPS13Bgene.
Thisfindingrefinedtheunderstandingofgenotype-phenotypecorrelation.
Conclusions:ThisisthefirstreportofaTunisianfamilywithCohensyndromemutatedintheVPS13Bgene.
Keywords:Cohensyndrome,VPS13Bgene,CompoundheterozygousmutationBackgroundCohensyndrome(CS)(MIM#216550)isarareautosomalrecessivedevelopmentaldisordercharacterizedbyCohenandcolleaguesin1973[1].
Truncalobesity,intellectualdisability,developmentaldelay,jointlaxity,craniofacialdysmorphism,highmyopiaand/orretinaldystrophyandneutropeniaaretypicalclinicalmanifestationsofthesyn-drome[1,2].
Atpresent,CShasbeenessentiallyassignedtomutationsintheVPS13Bgene(MIM#607817)amongpatientsfromdiverseethnicity.
VPS13B,thesingleCSlinkedgenesofardescribed,islocalizedonq22.
2locusofchromosome8.
Itslengthisabout864kbandcomprises62exons.
Thelongesttranscript[NM_017890.
4]is14,100bplongencodingfora4022aminoacidprotein.
VPS13Bisaperipheralmembraneproteinwithputativetransmembranedomainsandfunctionalmotifsthathaveanessentialfunctioninthetransportofintracellularpro-teinsandinvesicle-mediatedsorting[3].
TheexpressionoftheVPS13Bismainlynoticedinthewholebodyandinthecentralnervoussystem,blood,muscles,andheart[4].
Approximately,200casesoftheCSandaboutmorethan150deleteriousmutationshavebeenidentifiedtodate(http://www.
hgmd.
org);inmostcasesmutationsarestopcodonmutationsthatresultinafunctionallynullprotein.
Thediagnosisisalwaysdifficultinchildhood,thisisduetothefactthatmanyofthetypicaltraitsmaybenonexis-tenttillscholarisationorupcomingyearsandintermittentneutropeniaisnotconsistentlyobservable.
HerewereportthecharacterizationofanewcompoundheterozygousmutationinVPS13Bgenein2TunisianrelatedcaseswithCS.
*Correspondence:imen_rejeb@yahoo.
fr;imen.
rejeb@rns.
tn1ServicedesMaladiesCongénitalesetHéréditaires,CHUMongiSlimLaMarsa,SidiDaoudLaMarsa,2046Tunis,TunisiaFulllistofauthorinformationisavailableattheendofthearticleTheAuthor(s).
2017OpenAccessThisarticleisdistributedunderthetermsoftheCreativeCommonsAttribution4.
0InternationalLicense(http://creativecommons.
org/licenses/by/4.
0/),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedyougiveappropriatecredittotheoriginalauthor(s)andthesource,providealinktotheCreativeCommonslicense,andindicateifchangesweremade.
TheCreativeCommonsPublicDomainDedicationwaiver(http://creativecommons.
org/publicdomain/zero/1.
0/)appliestothedatamadeavailableinthisarticle,unlessotherwisestated.
Rejebetal.
BMCMedicalGenetics(2017)18:134DOI10.
1186/s12881-017-0493-5CasepresentationThepresentstudydescribesclinicalandmolecularfindingsintwopatientswithCSfromanon-consanguineousTunis-ianfamily.
Oneoftheauthorsexaminedthepatients.
DNAwasextractedfromperipheralbloodusingstandardmethods.
Thepatients'parentsgavetheirconsent.
Thepropositawasthefirstchildofnon-consanguineousandhealthyconditionparents.
PregnancywasnormalandcarriedtotermwithanAPGARscoreof9and10atoneandfiveminutesafterbirth,respectively.
Theparametersatbirthwere:weight3300g(60thpercentile),height50cm(70thpercentile),occipitofrontalcircumference(OFC)35cm(85thpercentile).
Hypotoniaandpoorsuckingwerenoticed.
Shepresenteddelayedpsychomotordevelopment:shewasn'tcapabletositwithouthelptill12monthsandwalkedattheageof2years.
At3years,thepatientwasnotcapabletospeak.
Ophthalmologicalevaluationshowedleftstrabismusandpigmentaryretinopathy.
Whenreevaluatedat12years,growthretardationandprogressivemicrocephalywerenoted.
Wenoticedaweightof31kg(1SD),aheightof126cm(3.
2SD)andanOFCof48cm(3.
8SD).
Atneurologicalassessment,wenoticedwidespreadhypotoniaandjointhypermobility.
Clinicaldiagnosisrevealeddysmorphicfacialfeaturesasthickhaireyebrowsandlashes,prominentuppercentralincisors,prominentlipsandshortphiltrum;thelasttwofeaturesleadtoahalfopen-mouth.
Thehandsweresmallwithta-peringfingers.
Shealsopresentedtruncalobesity(Fig.
1).
Communicationandsocialskillswereimpaired.
Shepresentedintellectualdisabilitywithautistic-liketraits.
CerebralMRIshowedthickanddysmorphiccorpuscal-losumandlateralventricularasymmetry.
Thebrainstemandthecerebellumwerenormal(Fig.
1c).
KaryotypeandCGHarraywerenormal.
Herbrotherpresentedattheageof6yearsaweightof22kg(normal),aheightof113cm(normal)andanOFCof48cm(3SD).
Birthparameterswere:weight3350g(50thpercentile),height50cm(50thpercentile),occipitofrontalcircumference(OFC)36cm(85thpercentile).
PregnancywasnormalandcarriedtotermwithanAPGARscoreof10and10atoneandfiveminutesafterbirth,respectively.
Hewasbornwithaptosisinthelefteyeoperatedattheageof5years(Fig.
1).
Hepresentedhighmyopia.
Hehad,likehissister,thickhaireyebrowsandlashes,hepresenteddownslantedpalpebralfissures,micrognathia,archedpalate,clinodactylyofthetoes,slenderhandsandfeetandtaperingfingers.
Intellectualdisabilityandstereotypedmotorbehav-iorwerealsonoticed.
Aftertheidentificationofthecausalmutation,thereversephenotypingshowedmoderateneutropeniaandmildneutropeniainthepropositaandherbrotherrespectively.
Infact,neutropeniaisoneoftheimportantclinicalsignsofCS,butbecauseofthenonexistenceofclinicalsignsandtheoccasionaloccurrence,itisrarelyidentified.
TheCAREguidelineswerefollowed.
GenetictestingBecauseoflimitationsofrenseignementonneutropeniaandpigmentaryretinopathywedidn'tnoticethattheclinicalfeaturesmatchedwithaCS,sowefirstuseWESapproach.
WeperformedWESintriomadeoftheprobandandhistwounrelatedparents.
Librarygeneration,exomeenrichmentandwhole-exomesequencingmethodologyusedaredetailedinthearticlewrittenbyPoirieretal.
[5].
Weanalyzedvariantsaffectingcodingregionsandessen-tialsplicingsitesandexcludedallvariantswithafrequencygreaterthan1%accordingtogenomicdatabases(dbSNP,1000Genomes,Exomevariantserverandlocalplatformdatabase).
AllrelevantvariantwerevisuallyexploredwithIntegrativeGenomicsViewer(IGV:http://software.
broadin-stitute.
org/software/igv/)todetectfalsepositiveresults.
Withthismethodandthesefilters,9variantswerede-tectedinindexcase(7withdenovomodelofinheritanceand2inthesamegenewithrecessivemodel).
5outofthe7"denovo"variantsappearedinheritedfromoneparent(IGV),the2otherswereabsentintheaffectedbrother.
The2variationsinVPS13Bgene(identifiedbyrecessivemodelofanalysis)werealsopresentinthebrother;thec.
3582delT,p.
A1194fswereinheritedfromthemotherandthec.
6295_6296delAT,p.
M2124fsonefromfather.
Finally,weconfirmedbyPCRandSangersequencingofallcodingregionsandexon-intronboundariesoftheVPS13BgenetherelevantvariantsidentifiedbyWES.
UsinggenomicabcFig.
1aTheproband.
bthebrotheroftheproband.
cProband'sMRI(1)sectionsshowingdysmorphicandthickcorpuscallosumand(2,3)thelateralventricularasymmetryRejebetal.
BMCMedicalGenetics(2017)18:134Page2of5DNAfromtheproband,herparentsandherbrother,themutationsidentifiedweretestedforfamilialsegregation.
WESofindividualII1noticedthepresenceofacompoundheterozygousvariant(100,479,778T/,100712001AT/)intheVPS13Bgene(Fig.
2a).
ThiscompoundheterozygousmutationintheVPS13Bgene(NM_017890.
4)wasvalidatedbySangersequencing(c.
3582delT,p.
A1149fs+c.
6295_6296delAT,p.
M2124fs)(Fig.
2b)inheritedfromhealthyheterozygousparentsconfirmsthediagnosisofCS.
Sangersequencingshowedthatthevariationsc.
3582delT(p.
A1149fs)andc.
6295_6296delAT(p.
M2124fs)intheVPS13Bgenepresentinboththeprobandandherbrotherwereofbiparentalorigin(Fig.
3).
DiscussionandconclusionsWereportaTunisianfamilyincludingtwosiblingswithdevelopmentaldelayandintellectualdisabilityharbouringanovelcompoundheterozygousmutationintheVPS13BgenebyWES.
Evenforanexperiencedclinician,thediagnosisofCSisdifficult.
InfactthissyndromeisarareautosomalrecessivedisorderanditisoftenimpossibletodiagnosisCSuntilmiddleorlatechildhood.
Thereforethephentotypictraitsareveryvariable,severalcouldbelack-ingtillscholarisationorupcomingyears.
CScanberetainedwhensixofeightphentotypictraitsarenoticedincludingdevelopmentaldelay,jointhypermobility,typicalCSfacialgestalt,highmyopiaand/orretinaldystrophy,microcephaly,truncalobesitywithslenderextremities,overlysociablebehaviourandneutropenia[6].
Howeversomeofthesefeaturescannotbeobservabletillscholarisa-tionorupcomingyears,likeretinaldystrophy,truncalobesityandoverlysociablebehavior,furthermorethetyp-icalfacialgestaltofprominentincisorsisalwaysabsent.
Infact,whenthegirlwasfirstseenat7yearsandtheboyat1year,respectively,theyhadpostnatal-onsetmicrocephalyanddelayeddevelopmentalmilestones,wedidn'tsuspecttheCSatthistimegivennootherrevealingtraits.
MutationsintheVPS13BgeneareresponsibleforCS.
ThenovelcompoundheterozygousmutationinVPS13Binher-itedfromhealthyheterozygousparents,c.
3582delT(p.
A1149fs)andc.
6295_6296delAT(p.
M2124fs)inheritedrespectivelyfromthefatherandthemotherarepresentintheprobandandherbrothercausesaframeshiftthatinduceaprematurestopcodon.
SubsequentlythisframeshiftmutationgenerateaprematurestopcodonthatcaneitherinduceatruncatedproteinlackinganumberoffunctionaldomainsoftheVPS13Bproteinortoafunctionalnull-alleleasaresultofanonsensemediatedmRNAdecay(NMD).
Actually,approximately188mutationsinVPS13Bgenehavebeenidentified,153ofthemwereassociatedwithCS(http://www.
hgmd.
org/).
VPS13BisaGolgi-associatedper-ipheralmembraneproteinco-localizingwiththecis-GolgimatrixproteinGM130.
RP2andRPGR,tworetinitispigmentosadiseasegenes,situatetotheGolgi,anddepletionofRP2causesabnormalGolgifunctionandproteintransportinthephotoreceptor[7,8].
ThishighlightsthatanormalfunctionofGolgi-associatedproteins,includingVPS13B,isessentialforagoodfunctioningofthephotoreceptor.
RecentstudieshaveconcludedthatVPS13Bmutations,responsibleforCOH1,areresponsibleofatissue-specificmajordefectofglycosylationandendosomal–lysosomaltraffickingdefect.
ThishighlightsthatVPS13BisessentialinGolgiglycosyla-tionandmorphology,aswellasinlysosomal–endosomalpathwaymaintenance[9].
UsingWESintheearlystageofdiseaseforyoungpatientswheretheclinicaldiagnosisisnotevidentisactuallythebestapproach.
Currently,theexomesequen-cingapproachesareusedinmanylaboratorieshelpingFig.
2aIntegrativeGenomicsViewerofshortreadalignmentindicatedthecompoundheterozygousvariantidentifiedbyexomesequencing(100,479,778T/,100712001AT/)intheVPS13Bgene.
bSangervalidationshowsthecompoundheterozygosityoftheprobandII1formedbythec.
3582delTmutation,andthec.
6295_6296delATmutationRejebetal.
BMCMedicalGenetics(2017)18:134Page3of5cliniciansinsolvingtheaetiologyofmanyrarediseases.
Thisapproach,comparedtosangersequencinghelpssavingcostsandtimeespeciallyforlargegenessuchasVPS13Bgene.
Infact,thecostsofsequencingperbasewithsangersequencingismuchhigherthanwithNGS[10,11].
So,sangersequencingwillbeperformedonlyifacausativemu-tationwillbeidentifiedbyNGSinordertovalidatethisvariant.
Therefore,formendeliandiseases,especiallyforthosewithgeneticheterogeneity,NGSisalmostcertainlythebestprimarychoiceingenetictests.
Inconclusion,wereportthefirstTunisianfamilywithCS,anovelcompoundheterozygousmutationinVPS13Bgene,identifiedusingWESisthedeleteriousmutationinthepatientsofthisfamily.
AbbreviationsAPGAR:Appearancepulsegrimaceactivityandrespiration;CGH:Comparativegenomichybridization;CS:Cohensyndrome;MRI:Magneticresonanceimaging;NGS:Next-GenerationSequencing;NMD:Nonsense-mediatedmRNAdecay;OFC:Occipitofrontalcircumference;PCR:Polymerasechainreaction;WES:WholeexomesequencingAcknowledgmentsWewouldliketothankthefamilymembersfortheirinvaluablecooperationandparticipation.
FundingNotapplicable.
AvailabilityofdataandmaterialsAlldatageneratedoranalyzedduringthisstudyareincludedinthispublishedarticle.
Authors'contributionLBandJCdesignedandinitiatedthestudy,monitoreddatacollectionandanalysisforthestudyandrevisedthepaper.
IRcontributedtosamplecollection,analyzedclinicaldata,anddraftedthepaper.
HJ,YEandSHcontributedtocollectionofclinicalandimagingDataandgeneticcounseling.
JLZanalyzedtheWESdataandrevisedthepaper.
LHhelpedwithtechnicalpartsandrevisedthepaper.
Allauthorsreadandapprovedthefinalmanuscript.
EthicsapprovalandconsenttoparticipateThisstudywasapprovedbytheEthicsReviewCommitteeCHUMongiSlimLaMarsainTunisiaandinformedconsentwasobtainedfromthepatients'parentspriortoparticipation.
ConsentforpublicationConsentforpublicationofrespectivecasepresentationswasobtainedfrompatients'parents.
Theygivetheirconsentforthepublicationofthemedicaldataandphotosoftheirsonanddaughter.
CompetinginterestsTheauthorsdeclarethattheyhavenocompetinginterests.
Publisher'sNoteSpringerNatureremainsneutralwithregardtojurisdictionalclaimsinpublishedmapsandinstitutionalaffiliations.
Authordetails1ServicedesMaladiesCongénitalesetHéréditaires,CHUMongiSlimLaMarsa,SidiDaoudLaMarsa,2046Tunis,Tunisia.
2LaboratoiredeGénétiqueHumaine,FacultédeMédecinedeTunis,Tunis,Tunisia.
3InstitutCochin,UniversitéParis-Descartes,CNRS(UMR8104),Paris,France.
4Inserm,U1016,Paris,France.
5Pledebiologie,HpitauxUniversitairesdeStrasbourg,Strasbourg,France.
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