X-LAG: How did they grow so tall?

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X-LAG:

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Albert

Beckers

a,∗

,

Liliya

Rostomyan

a

,

Iulia

Potorac

a

,

Pablo

Beckers

b

,

Adrian

F. Daly

a

a_Department_of_{Endocrinology,}_Centre_Hospitalier_{Universitaire}_de_Liège,_University_of_Liège,₄₀₀₀_Liège,_Belgium b_Department_of_Clinical_{Biochemistry,}_Centre_Hospitalier_{Universitaire}_de_Liège,_University_of_Liège,₄₀₀₀_Liège,_Belgium

Abstract

X-linkedacrogigantism(XLAG)isanew,pediatric-onsetgeneticsyndrome,duetoXq26.3microduplicationsencompassingtheGPR101gene. XLAGhasaremarkablydistinctphenotypewithdiseaseonsetoccurringbeforetheageof5inallcasesdescribedtodate,whichissignificantly youngerthaninotherformsofpituitarygigantism.ThesepatientshavemixedGHandprolactinpositiveadenomasand/ormixed-cellhyperplasia andhighlyelevatedlevelsofGH/IGF-1andprolactin.Giventheirparticularlyyoungageofonset,thesignificantGHhypersecretioncanleadto aphenotypeofseveregigantismwithveryadvancedage-specificheightZ-scores.Ifnotadequatelytreatedinchildhood,thisconditionresultsin extremefinaladultheight.XLAGhasaclinicalcoursethatishighlysimilartosomeofthetallestpeoplewithgigantisminhistory.

Keywords: Gigantism;Pituitaryadenoma;X-linkedacrogigantism(X-LAG);GPR101gene;Familialisolatedpituitaryadenoma(FIPA) Résumé

«X-linkedacrogigantism»(XLAG)estun syndromepédiatriquerécemmentdécrit, liéàdesmicroduplications duchromosome Xq26.3, englobantlegèneGPR101,responsabledel’affection.LespatientsXLAGprésententunphénotyperemarquablementdistinctdesautrescasde gigantismehypophysaire.Danstouslescasdécrits,lamaladies’exprimeavant5anssoitbeaucoupplustôtquedanslesautresformes.Lespatients onthabituellementungrosadénomeouunehyperplasiemixtepourlaGHetlaprolactineetdestauxtrèsélevésdeGH/IGF1etprolactine.Enraison desondébuttrèsprécoce,l’hypersécrétionimportantedeGHpeutconduireàungigantismeextrêmementsévèreavecunZ-scoretrèsimportant pourl’âge.Sicetteconditionn’estpastraitéependantl’enfance,ellepeutconduireàunetaillefinaleextrême.XLAGmontreuneévolutionclinique similaireàcelleobservéechezlesgéantslesplusgrandsdel’histoire.

Motsclés :Legigantisme;L’adénomehypophysaire;L’acro-gigantismeliéauchromosomeX(X-LAG);LegèneGPR101;L’adénomehypophysairefamilial isolé(FIPA)

1. Introduction

Acromegaly and gigantism result from chronic excessive

productionandsecretionofgrowthhormone(GH),usuallyby

apituitaryadenoma,andare consideredveryrare conditions.

GH-secreting pituitary tumors are predominantly sporadic

∗_{Corresponding}_author.

E-mailaddress:albert.beckers@chu.ulg.ac.be(A.Beckers).

lesionsthatoccurinadults,althoughrarepediatricorfamilial formscanoccurandthesecanhaveaggressivecharacteristics.

The molecular genetics of these aggressive forms of

soma-totropinomas is of interestfor research andclinical practice.

Known genetic syndromes associated with the occurrence

of somatotropinomas include multiple endocrine neoplasia

(MEN)type1andMEN4,Carneycomplex,McCune–Albright

syndrome(MAS),andpheochromocytoma/paragangliomaand

pituitaryadenomasyndrome(3PAs).Themostfrequentfamilial

formofpituitaryadenomaisfamilialisolatedpituitaryadenoma

http://dx.doi.org/10.1016/j.ando.2017.04.013

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Fig.1.Growthpattern(panelA)andphysicalcharacteristics(panelB)ofapatientwithXq26.3duplication.Shewasborntonormally-sizedparentsinafamily withoutahistoryofgigantismandhadalreadyestablishedabnormallineargrowthandacralovergrowthbytheageof12months,causedbyaGH-and prolactin-secretingpituitarytumor[4].

(FIPA) syndrome [1]. Approximatively 15–20% of general

FIPAkindredsandabout50%ofhomogeneousFIPAfamilies

withacromegaly-gigantismare causedbymutations/deletions

inthearylhydrocarbonreceptorinteractingprotein(AIP)gene

[2,3].

In Trevellin et al., we recently described an international cohortof patientswithanewgeneticformofpituitary gigan-tismbeginninginearlychildhoodduetoamicroduplicationon

Xq26.3,thatwetermedX-linkedacrogigantism(XLAG)[4].In

alargepituitarygigantism-specificcohortstudyof208patients,

we found that AIP mutations andXLAG accountedfor 29%

and 10%, respectively, of geneticallytested patients, making

them the two most common causes of pituitary gigantism.

Thepreviouslyknowngeneticcausesofsomatotropinomasare

responsible for a much lower percentage of pituitary

gigan-tismcases:MAS(5%),MEN1(1%),andCarneycomplex(1%)

[5].To date,32 patients withXLAG duplications have been

publishedinthescientificliterature[4,6–11].Notably,XLAG explainsthemajorityofprepubertalcases(80%)andalmostall ofthetallestcasesinour208-patientcohort;theseXLAGcases

manifestedwitheitherexceedinglyexcessivegrowthrateora

veryincreasedfinaladultheight(heightZ-score>+4.5SD).

2. Clinicalproﬁle

XLAGisapediatric syndromeofpituitarygigantismwith

a very young ageof disease onset. Usually increased length

andweightareseenbeforetheageof1yearandmostpatients

are diagnosedby the age of three with already substantially

advanced overgrowth [4,9,12]. This young age at first

mani-festations renders this particular form of gigantism different

fromotherformsofgigantismandacromegaly.Geneticformsof

somatotropinomas,particularlyAIP-related,aremorefrequent

in younger patients than in the general sporadic acromegaly

population [5]. AIP-related cases, however, usually occur in

adolescentsand young adults, whereas childrenwith XLAG,

whoareusuallyborn withnormalanthropometric parameters

afteruncomplicatedpregnancies,begintheirabnormalgrowth

ininfancy(Fig.1A)[4].ThismeansthatpatientswithXLAG

canhavehadalongdurationof overgrowthbythe timethey

reachpuberty,whichtranslatesintoincreased heightZ-scores ascomparedwithotherformsofpituitarygigantism[5].

Besidestheearlyexcessiveaccelerationoflineargrowthand bodysize,theseyoungpatientsfrequentlypresentsomeclinical

signsandsymptomsofGH/IGF-1excessthataremoretypical

of adultacromegaly (Fig. 1B).They maydevelopsoft tissue

swellingandcoarsefacialfeaturesandanincreasedinterdental

space,aswellas markedenlargementof handsandfeet [12].

In somecases, increased appetite (25%) andsigns of insulin

resistance (such as acanthosis nigricans) are also noticed at

diagnosis[12].XLAGhasafemalepredominance(71%);this

feature differentiates it from AIP-mutation related gigantism

casesandgigantismpatientswithoutaknowngeneticcausein

whichcasesmostoftheaffectedsubjectsaremales(95%and

78%,respectively)[5].

In both male and female XLAG cases, the extraordinary

growth velocity and prolonged linear growth is underpinned

bytheaggressivebehaviorofthepituitarylesion[4,12].

Chil-drenwithXLAG developrelatively largepituitary adenomas

for their young age (Fig. 2), which can be accompanied by

pituitaryhyperplasia.Insomecases,diffusehyperplasiacanbe presentaloneanditisunknownwhetherthemixedGH-prolactin

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Fig.2.CoronalandsagittalMRIimagesofpatientswithXLAG.PanelsAandB.Alargepituitarymasswithimportantsuprasellarextensioninafemalepatient wasrevealedbygadolinium-enhancedMRimagingatdiagnosis(2years11months).PanelsCandD.Gadolinium-enhancedMRimagesofafemalepatient,who wasdiagnosedatage3yearswithalargepituitarymasswithmarkedsuprasellarandposteriorextensionandareasofdegenerativechanges.PanelsEandFshow postoperativeimagesfromthesamepatientwithresectedadenoma.However,theadministrationofSSAandpegvisomantwererequiredaftersurgeryinthispatient forhormonalandgrowthcontrol.PanelsGandHshowMRimagesofafemalepatientatdiagnosis(aged3years)presentingwithalargepituitarymasswith extrasellarexpansion[12].

secretingmacroadenomasthatareseeninmostXLAGpatients

beginashyperplasiabeforetransformingintoadenoma.

Pathol-ogy studies have demonstrated foci of transformation from

hyperplasia to adenoma, which further supports the concept

thatthe adenomasinXLAGdevelopagainstabackgroundof

hyperplasia[4,7,12,13](Table1).

WerecentlyshowedthatmodestlyelevatedcirculatingGH

releasing hormone (GHRH) levels can occur in XLAG[13].

GHRH levels in XLAG are not as high as those usually

encountered inectopicGHRH secretionfromneuroendocrine

carcinomas. Moreover, intense GHRH-receptor (GHRH-R)

stainingwasfoundinresectedpituitarytumortissueinXLAG

Table1

Historicalcasesofextremegigantisminwhichgrowthbeganinearlychildhood[12].

Name Country Sex Yearofbirth Birth

weight(kg) Normal family history Ageatwhich abnormalgrowth noted(years) Finalheight(cm)

MartinVanBurenBatesa _USA _M ₁₈₃₇ _Normal _Y ₆ ₂₂₂

AnnaHainingSwana _Canada _F ₁₈₄₆ _8.1 _Y _<₄ ₂₂₇

EllaKateEwing USA F 1872 3.4 Y 7 225

FedorAndreevichMachnow Russia M 1878 NA Y 5 239

EdouardBeaupréb _Canada _M ₁₈₈₁ _4.1 _Y ₃ ₂₅₁

Joh(a)nAasenb _USA _M ₁₈₉₀ _NA _No _<₈ ₂₁₈

AlbertJohanKramerb _The_Netherlands _M ₁₈₉₇ _8.5 _Y _<₇ ₂₃₈

RobertPershingWadlowb _USA _M ₁₉₁₈ _4.1 _Y _<₃ ₂₇₂

CecilBoling USA M 1920 Normal Y <7 235

RigardusRijnhoutb TheNetherlands M 1922 Normal Y >3 238

DoloresAnnPullardb USA F 1946 Normal Y 4 227

SandraElaine(Sandy)Allenb USA F 1955 2.95 Y 3 232

ZengJinlian China F 1965 Normal Y <1 249

YaoDefenb China F 1972 2.8 Y <3 234

a_Swan_and_Bates_were_married_and_had_two_pregnancies;_one_female_child_was_stillborn_(weighed_8.1_kg)_and_later_a_son_who_died_in_early_infancy_was_10.8_kg and76cminlengthwhenborn.

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Fig.3.Photographsofsomeofthetallesthistoricalpatientspresentedintheorderoftheirheight.Theyappearedfrommedicalrecordsashavingearlychildhood-onset pituitarygigantism,whichisanimportantfeatureoftheXLAGsyndrome.Twogreysilhouettesillustratetheaveragehumanheight(175cm).

[4,12,13];whichsuggeststhatthe cellpopulationinvolvedin

hyperplasiaandadenomatoustransformationmaybesensitive

toGHRH.Furthermore,invitrocellculturestudiesofanXLAG

pituitarylesion revealedthat a GHRH-R antagonist inhibited

both GHand prolactin and antagonised the effect of GHRH

stimulation.Thesedatasupporthypothalamicinvolvementvia

GHRH and GHRH-R dysregulation in the pathogenesis of

XLAG.TheGHRH-relatedGHhypersecretioninXLAGcould

potentiallybetargetedbytherapeuticblockadeoftheGHRH-R

[13].

Intermsoftreatment,XLAGpatientshaveparticularly dif-ficult to treat pituitary lesions, not only due to their young ageandrelativelylargetumorsize.They oftenrequire multi-modaltreatment,includingpituitarysurgery,medicaltreatment

andradiotherapy.AlmostallXLAGcaseshavepartialor

com-pleteresistancetooctreotide/lanreotide,despitearelativelyhigh expressionofsomatostatinreceptortype2[12].Prolactin

hyper-secretion demonstrates variable responsiveness to dopamine

agonist therapy. In ordertocontrol GHhypersecretion,some

patients have required aggressive surgical resection

(includ-ing anterior hypophysectomywhen extensivehyperplasiahas

been present), incombination with radiotherapy. The

conse-quences of these multiple lines of treatment is the frequent

occurrence of partial or complete hypopituitarism, requiring

lifelong replacement therapystartingfrom avery youngage.

Adjuvant use of the GH receptor antagonist, pegivsomant,

has proven successful in controlling GH secretion in some

XLAGpatients[12].Promptandeffectivehormonalcontrolis

akeyrequisiteinhaltinglineargrowthbeforepatientsreacha markedlyincreasedadultheight[5].Intheabsenceofeffective

measurestocontroltumorgrowth,markedtumorprogression

cancontinue inXLAG,withexceptionallyseverephenotypes

of pituitary gigantism being established before puberty [7].

A number of patients with extremelygigantism described in

historical andmedical records had clinical presentationsthat

correspondedtothe growthpattern of XLAGpatients [4,12].

In particular, the tallestman, RobertWadlow, andthe tallest

woman,ZengJinlian,inrecordedhumanhistorypresentedthe

characteristicsofXLAGpatientswithrapidovergrowthinearly childhood(Fig.3).

3. Genetics

XLAGhasaspecificgeneticetiology.Unliketheother

pitu-itaryadenoma-associatedgeneticsyndromesusuallycausedby

inactivatingmutationsordeletionsintumorsuppressorgenesor

activatingmutationsinanoncogene,XLAGisduetoa

dupli-cation on chromosome Xq26.3. Array comparative genomic

hybridization(aCGH)isusually usedfordetectingsuchcopy

numbervariation(CNV)abnormalities.All18XLAGpatientsin

ourinitialcohortwerefoundtohavemicroduplicationswithtwo

smallestregionsofoverlap,encompassingfourgenes(CD40LG,

ARHGEF6,RBMXandGPR101)[4].Amongtheinitialfour

can-didategenes,GPR101,an orphanG-protein coupledreceptor

gene,wasshowntobetheonlyonesignificantlyoverexpressed inthepituitarytissueofpatientswithXq26.3microduplications.

Thecausativepathogenicroleof the GPR101gene inXLAG

wasthereaftersupportedbyaXLAGpatientwithduplicationof

GPR101alone[8].

GPR101 is anorphan Gsprotein-coupledreceptor, whose

endogenousligandandexactfunctionsareunknown.GPR101

isnormallyexpressedatparticularlyhighlevels inthemouse hypothalamusandinthepituitaryoftherhesusmacaqueandthe

rat.Inhumans,GPR101mRNAispredominantinthenucleus

accumbens anditsexpression islow inadultpituitarygland.

However,GPR101mighthavearoleduringpituitary

ontoge-nesis.GPR101 expressionwasfoundinthepituitaryglandof

humanembryosstartingfrom19weeksofgestationalagewith

thehighestlevelsofGPR101staining(65%)at38weeks[4,14].

GPR101duplicationmightsupportmixedGHandprolactin pos-itivecellularhyperplasiainXLAGstartingfromthefetalperiod withfurtheradenomaformationintheearlyperiodafterbirth.

However,theroleofGPR101inpituitarydevelopment,

tumori-genesisandstimulationofGH/prolactinhypersecretionremains

unclear.Sofar,inactivatingmutationsoftheGPR101genedo

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Fig.4.GenomicgainsonHD-aCGHinthreesporadicmales.ThetheoreticalLogratio(LR)valueofheterozygousduplicationonXchromosomeinmalesismarked astheredline.TheLRvaluesoftheXLAGduplicationsidentifiedineachsubject(blacklines)werefoundtobelowerthanthetheoreticalLRinallthreecases[9].

MostXLAGcasesaresporadicandduplicationsinall

spo-radiccasesappeartobenon-recurrentwithuniqueboundaries.

ThesearegenerallyduetoaDNAreplicationerrorbecauseof

microhomologiesbetweenproximatefragmentsatXq26.3[4].

Infamilialcases,atransmissionofthe sameXLAG

microdu-plication from affected mother to affected son with 100%

penetrancehasbeenreportedinthreehomogeneousFIPA

kin-dreds withearlyonset acrogigantism[4,11].Along withAIP

mutation/deletion,XLAGisthesecondknowngeneticcauseof

FIPAinAIP-negativekindredswithfamilialacrogigantism.

While the GPR101 duplication has been found in all the

XLAGcasesreportedsofar,insporadicmalestheaCGHresult

demonstratesthepresenceofsomaticmosaicismthatleadstoa variableproportionofaffectedcells(Fig.4)[9].Relativelylow levelsofGPR101duplicatedcells(aslowas16–17%)havebeen

confirmedusingdigitaldropletPCR(ddPCR),whichallowsthe

detectionof quitesmallrates of mutationsor CNV–deletions

or duplications (Fig. 5). The clinical presentation of XLAG

inallmosaiccasesissimilartothatof patientswith constitu-tionalduplication,intermsofovergrowthandpituitarydisease

severity. Thus, sporadic males could exhibit dramatic forms

of pituitary gigantism even when only a low proportion of

cellscarrytheGPR101duplication.Wescreenedalargegroup

of patients with acromegaly andgigantismusing quantitative

ddPCRforGPR101duplications.Thismethodallowsthe

iden-tificationofnewXLAGcasesbymeansofincreasedGPR101

copynumber,whichcanlaterbeconfirmedonaCGH[9].

Recently,wefurtherappliedthisscreeningddPCRmethod

toancientDNAretrievedfromskeletalremainsofahistorical

caseofextremeacrogigantism(giantConstantin;259cm).The

individualdiedofsepticemiafollowingsurgeryforgangreneas ayoungadultin1902,andhisautopsydemonstratedamassively enlargedpituitaryglandandpituitaryfossa[10].Accordingto

published sourcesand original medical documentation

avail-abletous,theabnormalgrowthstartedearlyandextremelytall stature(1.94m)wasalreadypresentattheageof14.

Paleonto-logicalDNAextractiontechniquespermittedtheextractionof

DNAfrombonepowderandsubsequentddPCRrevealed

ele-vatedcopynumberofGPR101indicatingaprobablediagnosis

ofXLAG(Fig.6).

Fig.5.Mosaicism-levelquantificationbyHD-aCGH(panelA)andddPCR(panelB)insporadicfemales(averagemosaicismlevelin11cases),familialfemale (1case),familialmales(3cases)andsporadicmales(3cases)withXLAGsyndrome[9].

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Fig.6. Ahistoricalcaseofdramaticgigantism,thegiantConstantin,whomeasured259cm.HewasphotographedforaposterwhilevisitingBelgiumin Novem-ber1901,atwhichtimehehadextremelytallstatureandacromegalicfeatures(panelA).Aphotographofhisskullfrom1904(panelB)showsmarkedprognathism andenlargementofthemalarbones.AnenlargedsellaturcicaismarkedbytheopenarrowonpanelCshowinganinteriorviewofthesubject’scranium.DNAwas obtainedbydrillingasmallamountofbonepowder(filledarrow)[10].

4. Conclusion

XLAGsyndromeischaracterizedbyaveryspecific

pheno-typeofinfant-onsetgigantismwithmarkedlyincreasedheight

andweightz-scores.It iscausedbymixed GHandprolactin

secretingpituitaryadenomas and/orhyperplasiathat can

pro-duceexceptionallyhighlevelsofGHandprolactin.Thisnew

genetic from of pituitarygigantism is due tothe duplication

of the GPR101 gene andcan present either sporadically (as constitutional or mosaicduplication) orinaFIPA setting.To

date,32XLAGpatientshavebeenreported,mostofwhomare

females.XLAGisaclinicalentitythat,whilerare,leadstoan exceptionallyseverepituitarygigantismphenotypethatrequires earlyinterventiontocontrolovergrowth.

Disclosureofinterest

Theauthorsdeclarethattheyhavenocompetinginterest.

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