Inheritance of arterial lesions in renal fibromuscular dysplasia

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1 (2007) 2, & 2007 Nature Publshng Group All rghts reserved /07 $ ORIGINAL ARTICLE Inhertance of arteral lesons n renal fbromuscular dysplasa J Perdu,2, P Boutouyre 3,4,5,0, C Bourgan 6,7,0, N Stern,8, B Laloux 4, E Bozec 4, M Azz 3,8, C Bonat-Pellé 6,7, P-F Ploun 2,3,9, S Laurent 3,4,5, A-P Gmenez-Roqueplo,2,3 and Jeunematre,2,3 AP-HP, Department of Genetcs, Hôptal Européen Georges Pompdou, Pars, France; 2 INSERM, Unt 772, Collège de France, Pars, France; 3 Faculté de Médecne, Unversté Pars Descartes, Pars, France; 4 AP-HP, Department of Pharmacology, Hôptal Européen Georges Pompdou, Pars, France; 5 INSERM, Unt 337, Pars, France; 6 INSERM, Unt 535, Vllejuf, France; 7 Unversté Pars-Sud, Vllejuf, France; 8 AP-HP, Hôptal Européen Georges Pompdou, Clncal Investgaton Center CIC920, Pars, France and 9 AP-HP, Department of Hypertenson, Hôptal Européen Georges Pompdou, Pars, France We have prevously shown that patents wth renal fbromuscular dysplasa (FMD) have asymptomatc carotd lesons and that famlal forms may occur. The objectve of ths study was to test whether carotd lesons could be detected n relatves of famlal cases. Hgh-resoluton echotrackng of the carotd artery was performed n 47 relatves of 3 cases from sx famles. Ths non-nvasve nvestgaton led to a semquanttatve arteral score that was compared wth that obtaned for 47 controls matched for age and sex and that for 25 sporadc cases. Famlal resemblance was tested by usng a generalzed estmatng equaton approach takng nto account the clusterng of scores n famles. As expected, FMD cases had a sgnfcantly hgher score than controls (4.02 vs 2.52, Po0 5 ). Famlal cases were not sgnfcantly dfferent from sporadc cases. Of nterest, the 47 apparently healthy relatves of famlal cases had also a hgh carotd score (4.7), very sgnfcantly hgher than that of controls (2.52, Po0 5 ) even though lower than the correspondng ndex FMD cases (4.8, P ¼ 0.0). Segregaton analyss showed that 52% of the descendants of subjects wth a score 44 had a score 44, a proporton consstent wth autosomaldomnant transmsson of the trat. Altogether these results strengthen the hypothess of renal FMD beng a systemc arteral dsease and argue for a famlal resemblance that may be due to a major genetc effect. The carotd score obtaned by hgh-resoluton echotrackng may provde a non-nvasve surrogate marker for renal FMD of potental value for use n lnkage strateges on large pedgrees. (2007) 2, do:0.038/sj.jhh.00256; publshed onlne March 2007 Keywords: genetcs; fbromuscular dysplasa; renovascular; echotrackng; arteral stffness; generalzed estmatng equaton approach Introducton Renal artery fbromuscular dysplasa (FMD) s a rare, non-atherosclerotc, non-nflammatory vascular dsease of truncal or branch kdney arteres, of unknown pathophysology. In medal FMD, the most prevalent form of FMD, pathologc examnaton shows successve areas of paretal thckenng (correspondng to medal hyperplasa) and dlataton (followng dsrupton of nternal elastc lamna). These arteral alteratons may lead to stenoses Correspondence: Dr J Perdu, Department of Genetcs, Hôptal Européen Georges Pompdou, 20-40, rue Leblanc, Pars Cedex 5, France. E-mal: jerome.perdu@egp.aphp.fr 0 These authors contrbuted equally to ths work. Receved 8 September 2006; revsed 28 November 2006; accepted 24 December 2006; publshed onlne March 2007 and saccular aneurysms. In medal FMD, renal artery lesons usually present as multple, multfocal stenoses wth ntervenng aneurysms causng a strng of beads appearance, whereas unfocal stenoses are usually assocated wth ntmal FMD. If renal artery stenoses are severe, FMD may result n renovascular hypertenson and, f dssecton occurs, n renal nfarcton.,2 Medal FMD occurs predomnantly n mddleaged Caucasan women, and a number of rsk factors have been dentfed n ths group of women: smokng habts, oral contraceptve ntake and genetc factors.,3 5 Medal FMD may present as a famlal dsease, defned as the presence of angographcally documented FMD n at least two frstdegree relatves. 6 It has also been suggested that FMD s transmtted as an autosomal-domnant dsease wth ncomplete penetrance and varable clncal symptoms. 7,8

2 394 Evdence of arteral wall subclncal lesons n relatves of FMD pedgrees Identfyng the genes responsble for FMD s therefore an approprate strategy for nvestgaton of the pathophysology of ths dsease. However, ths approach requres the dentfcaton of a relable phenotype for separatng unaffected and affected subjects, even n the absence of symptoms. Renal artery duplex sonography may be not senstve enough, especally n cases of non-stenotc lesons and computed tomographc or magnetc resonance angography have a poor specfcty n patents wth FMD. 9 Renal angography s an nvasve test and would be unethcal to use for the characterzaton of normotensve members of a pedgree. We recently showed, wth carotd artery hgh-resoluton echotrackng technques, that FMD s actually a systemc dsease and that subclncal lesons of the common carotd artery (CCA) wall are commonly found n patents wth renal artery medal FMD. An arteral phenotypc score of 2 (normal) to 7 (hghly abnormal) has been shown to be strongly assocated wth FMD. 0 In ths study, we used ths score as a surrogate marker for renal FMD phenotype, n the characterzaton of frst-degree relatves of affected subjects. We selected pedgrees contanng at least two patents wth angographcally proven renal FMD. We showed, usng a generalzed estmatng equaton (GEE) approach, that relatves of renal FMD famlal cases have sgnfcantly hgher arteral score values than matched controls, suggestve of the presence of subclncal arteral lesons. We performed a segregaton analyss n sx famles, treatng arteral score as a dchotomous trat. We found that score 44 was a hertable trat wth an autosomal-domnant mode of nhertance. Methods Patents and subjects Fourteen (6.%) of the 228 FMD patents referred to the Hypertenson Unt of our nsttuton snce 986 were consdered to correspond to famlal cases because at least one of the frst-degree relatves of these patents (the sster n 3 cases) also had angographcally proven renal FMD. Three of the 4 famles concerned were mpossble to trace, one could not be studed for geographcal reasons and two conssted of two FMD cases wth no lvng relatves. The relatves of the FMD cases n the eght remanng famles were asked to partcpate n a clncal research protocol based on a routne clncal examnaton, together wth arteral echotrackng and blood samplng for DNA extracton and analyss. These eght famles contaned 3 elgble relatves, of whom 26 refused to partcpate, 23 could not be contacted and 7 were wllng to partcpate but could not because of geographcal constrants. The fnal analyss ncluded 47 Caucasan relatves from sx pedgrees studed n detal (Fgure ). These subjects were compared wth 47 normotensve Caucasan control subjects matched for age and sex, who were recruted durng the same perod among the medcal staff members and ther famles. Control subjects known to be hypertensve were excluded. They underwent the same procedures, carred out by the same traned techncans (EB, BL), as FMD patents and relatves. The study was approved by our nsttutonal ethcs commttee (Approval CCPPRB Pars-Cochn # RBM ) and all subjects gave wrtten nformed consent. As prevously descrbed, for a part of ths cohort FMD 004 FMD 008 FMD FMD 25 FMD 074 FMD FMD-YES HT-YES HT-NO HT-UNK Fgure Structure of the sx renal FMD famles. Arteral phenotypc score s presented beneath each subject con. HT: hypertenson; UNK: unknown; FMD: renal fbromuscular dysplasa.

3 (N ¼ 04), each FMD patent underwent a standardzed medcal evaluaton. 6 The procedures followed were n accordance wth nsttutonal gudelnes. Echotrackng measurements Ths nvestgaton was performed n a controlled envronment kept at þ 227C, after the subject had remaned n a recumbent poston for 5 mn. Rght CCA was studed 2 cm beneath the carotd bfurcaton, wth a 7.5 MHz lnear array ultrasound probe (Pe Medcal 350, Maastrcht, The Netherlands) coupled wth an echotrackng system (Walltrack System, Pe Medcal), as descrbed prevously. We frst checked nter-observer reproducblty; the results were then read blnd by two observers (JP, PB), and the arteral phenotypc score was determned as descrbed prevously (Table, Fgure 2). 0 For each patent, relatve and control, we recorded several B-mode mages and RF sgnals graphs, to prevent mage-assocated readng errors. Even f only the measurements on rght CCA are presented n ths work, our echotrackng protocol systematcally ncluded the examnaton of proxmal nternal carotd artery and CCA 2 cm beneath the bfurcaton on both sdes. Moreover, presence of atherosclerotc plaques was systematcally recorded to avod any artfcal ncrease of the score. Statstcal analyss Comparsons of scores. Data were analysed n a generalzed lnear model framework. The arteral phenotypc score s regressed on covarates (sex, age) and to compare scores between groups (famlal vs sporadc cases, relatves vs controlsy), a bnary varable dscrmnatng the groups to be compared s added n the model. When all the ndvduals Table Mode of calculaton of carotd artery echotrackng score Type of abnormalty B mode Double-lne normal pattern (normal blood-ntma and meda-adventta acoustc nterfaces) Dotted pattern (dscontnuous blood-ntma acoustc nterface) Core pattern (dscontnuous addtonal acoustc nterface between the two normal lnes) Trple sgnal pattern (contnuous supernumerary acoustc nterface between the two normal lnes) Radofrequency sgnals Double sgnal (constant normal two-waved acoustc sgnal) Alternaton of double and trple sgnal over successve acqustons Trple sgnal (constant three-wave sgnal correspondng to an addtonal acoustc nterface) Total (range 2 7) A gven ndvdual s characterzed by B-mode score and radofrequency sgnal score. The mnmum score s 2, and the maxmum score s 7. Evdence of arteral wall subclncal lesons n relatves of FMD pedgrees ncluded n the regresson are ndependent (controls, sporadc cases), ths s strctly equvalent to a Student s t-test for comparng mean values of the score n the two groups, adjusted for the covarates. When several related ndvduals are ncluded (multple cases or multple relatves from a partcular famly), tests should account for t. Indeed, as we suspect a famlal correlaton of the score, neglectng the relatedness of the ndvduals would msestmate the varance of the regresson parameters and artfcally ether ncrease or decrease the sgnfcance of the tests. To account for subject relatedness, we used a GEE approach. 2 Brefly, let Y be the vector of score values for all n ndvduals n famly, Y ¼ðY ; ;...; Y ; nþ T where Y ; s the score of ndvdual from famly. Let be the matrx of the K covarates ncluded n the model for famly, ¼ (,y, k ) and k ¼ ð; k... ;n k Þ T where ;n k s the value of the Kth covarate for the n ndvdual of famly. b ¼ðb 0; ; b j; ; b k Þ s the vector of the K regresson parameters. For ndvdual j n famly, our model s: Y j ¼ b 0 þ b ;j þþb k;j k þ e j. EðY Þ¼m ¼ P b j j. The GEE estmator for b s ^b ¼ jp 0 S ~ Þ P 0 S ~ Y where ~S s the workng correlaton matrx of Y. Because we have no model for the famlal dependence of the score, we used the dentty matrx as a workng correlaton matrx n the calculaton of ^b ¼ð P 0 Þ ð P Y Þ. Ths corresponds to a lnear regresson analyss on ndependent observatons where the clusterng of data n famles s preserved. An estmate for the varance of ^b robust to the msspecfcaton of the famlal dependences of the score s varð^bþ ¼! 0 S ~ 0 ~ S! ðy ^m Þðy ^m Þ 0 ~S! 0 S ~ whch, f the dentty matrx s used for ~S ; can be reduced to varð^bþ ¼ 0!! 0 ðy ^m ÞðY ^m Þ 0 0! For each regresson parameter b j we tested the null hypothess. qffffffffffffffffffffffffffffff b j ¼ 0, wth a standard Student s t-test ^bj varð^b j Þ where the robust varance s used. 395

4 Evdence of arteral wall subclncal lesons n relatves of FMD pedgrees 396 Probe Radofrequency sgnal Two-dmensonal study Fgure 2 Echotrackng study showng a trple sgnal of the CCA wall n B-mode scan and n rado frequency mode. In normal arteral wall, ultrasound reflects off of two acoustc nterfaces (blood-ntma and meda-adventta), resultng n two reflected waves on RF graphs and a double-lne pattern on the grey-scale mage generated n two-dmensonal mode. The detecton of a permanent addtonal wave n RF mode (black arrow) and/or of a contnuous supernumerary lne n B-mode (whte arrow) between the two normal lnes s called trple sgnal. Ths pattern s observed n a hgh proporton of FMD patents, and the addtonal nterface corresponds to hstologc medal hyperplasa. Mode of transmsson. We nvestgated the mode of transmsson of renal FMD, usng the arteral score as a surrogate marker, by convertng the score nto a dchotomous trat, usng an optmal threshold of 4 to separate affected and unaffected ndvduals. We plotted recever-operatng characterstc curves, whch showed that a score 44 was assocated wth a maxmum specfcty of 97.8% and a senstvty of 65.9%. Only one control subject (2.%) had a score 44. As famlal cases were selected on the bass of there beng at least two affected cases n the famly, we could not run a classcal segregaton analyss usng the score as a trat. Instead, we based our nference on the transmsson pattern of the trat n offsprng of selected cases. Ths approach s condtonal on the nformaton regardng the selected cases, and s thus unbased even when famles are not selected at random. Results The sx FMD pedgrees contaned two affected tros of ssters and four affected pars (Fgure ). One of the affected tros had only one survvng frstdegree relatve, a brother, whereas the other fve kndreds provded 4 5 relatves spannng 2 3 generatons. Only one proband wth typcal multfocal FMD was male. The clncal and radologcal characterstcs of the famlal and sporadc cases of renal FMD (Table 2) were consstent wth publshed reports of female predomnance and moderate to severe hypertenson. Famlal cases more frequently dsplayed blateral and multfocal lesons than dd sporadc cases. Ten relatves were known to have hypertenson (2%). Cardovascular rsk factors of the four groups are detaled n Table 2. The dstrbuton of arteral phenotypc scores for the 3 probands and affected sblngs of the sx pedgrees studed, the 25 sporadc cases, the 47 relatves and ther matched control subjects s summarzed n Fgure 3. For these 232 subjects, we detected a robust effect of age ð^bage ¼ 0:02 wth P ¼ ), and a small but sgnfcant effect of sex (^bsex ¼ 0:28 and P ¼ 0.024) on arteral score. We therefore compared the scores n the dfferent groups, usng the followng regresson model: y ¼ b 0 þ b age þ b 2 sex þ b 3 group, where group s a bnary varable contrastng the two groups. The mean scores obtaned were 4.8, 4.02, 4.7 and 2.52 for famlal cases, sporadc cases, relatves of famlal cases and controls, respectvely. Table 3 presents the regresson parameters of the model used to compare scores between these groups. It also dsplays the P-value for the test of the null

5 Evdence of arteral wall subclncal lesons n relatves of FMD pedgrees a 4 Famlal FMD cases N = 3 5 FMD frst degree relatve N = 47 b Mean = Mean = 4.7 Number 2 Number c 25 Sporadc FMD cases N = 25 d 30 Control subjects N = Mean = Mean = 2.52 Number Number Fgure 3 Arteral phenotypc score dstrbuton for the 3 probands and affected sbs of the sx affected famles (a), ther 47 relatves (b), 25 sporadc cases of renal FMD (c) and controls matched to the relatves (d). Table 2 Clncal and radologcal characterstcs of Caucasan famlal and sporadc FMD cases, relatves and controls Sporadc cases Famlal cases Relatves Controls (n ¼ 25) (n ¼ 3) (n ¼ 47) (n ¼ 47) Age (years) Sex (% female) Blateral renal FMD (%) Multfocal lesons (%) Systolc BP (mm Hg) Dastolc BP (mm Hg) Hypertenson (%) BMI (kg/m 2 ) Smokng habt (%) Dyslpdema (%) Dabetes (%) Abbrevatons: BMI, body mass ndex; BP, blood pressure (before any treatment n famlal and sporadc cases); FMD, fbromuscular dysplasa. Data are expressed as mean7s.d. hypothess b 3 ¼ 0, correspondng to the comparson of mean scores adjusted for age and sex and corrected for famly clusterng. The scores of sporadc and famlal cases dffer wth statstcally nonsgnfcant trends (P ¼ 0.07), but both were sgnfcantly hgher than n controls (Po0 5 ). Relatves had sgnfcantly lower scores than dd famlal cases (P ¼ 0.04), but these scores dd not dffer sgnfcantly from those obtaned for sporadc cases (P ¼ 0.4). These results were not ntutve when mean scores were compared (.e. 4.8 vs 4.02, P ¼ 0.07; 4.8 vs 4.7, P ¼ 0.04), hghlghtng the mportance of correctng for famlal structure. Very nterestngly, scores n controls are sgnfcantly smaller than scores n relatves (Po0 5 ). Age dfferences between groups dd not confound the observed dfferences n scores. After splttng the populaton accordng to the medan of age of propostus, we performed an analyss of varance ncludng a populaton term (famlal, relatves, sporadc cases or controls), and an age term (below and above medan). Although ths analyss confrmed hgher scores n FMD patents, we dd not observe any nfluence of age, nor nteracton wth populaton term. There was no ndcaton that dfferent levels of atheroscleross could have affected our results. As

6 Evdence of arteral wall subclncal lesons n relatves of FMD pedgrees 398 Table 3 Regresson of score on age, sex and group, usng the GEE Regresson coeffcent P-value Groups (0 vs ) Intercept b 2 (s.d.) Age b (s.d.) Sex b 2 (s.d.) Group b 3 (s.d.) Group test b 3 ¼ 0 Sporadc cases vs famlal cases 2.88 (0.52) 0.02 (0.005) 0.38 (0.23) 0.73 (0.4) 0.07 Controls vs relatves.97 (0.56) 0.0 (0.009) 0.09 (0.34).64 (0.30) o0 5 Relatves vs famlal cases 3.8 (0.5) 0.02 (0.004) 0.07 (0.23) 0.52 (0.2) 0.04 Relatves vs sporadc cases 3.2 (0.36) 0.02 (0.005) (0.22) 0.7 (0.2) 0.40 Controls vs famlal cases 2.07 (0.69) (0.04) 0.2 (0.45) 2.33 (0.45) o0 5 Controls vs sporadc cases.70 (0.3) 0.02 (0.005) 0.0 (0.20).50 (0.8) o0 5 Abbrevatons: GEE, generalzed estmatng equaton; s.d., standard devaton. Values of estmated regresson parameters and assocated s.d. and P-value of the t-test for group coeffcent b 3 ¼ 0. Model s y ¼ b 0 þ b ageþb 2 sexþb 3 group, where group s 0 or. hypertenson may have been correlated wth ncreased ntma-meda thckness (IMT), and possbly wth a falsely hgh score, we assessed the nfluence of hypertenson on the scores of relatves of famlal cases (wth the model: y ¼ a þ b age þ b 2 sex þ b 3 HT). No sgnfcant effect was detected (P-value of b 3 test ¼ 0.32). In addton, the four groups were not dfferent concernng the ncdence of smokng habt and dyslpdema as well as for ther mean body mass ndex. Only, presence of dabetes melltus was more often present n famlal cases and relatves than n sporadc cases and control populaton (P ¼ 0.04, w 2 test). Its hgher frequency n FMD patents (7.5%) and ther relatves (8.5%) s probably a spurous fndng observed because of the observaton of a small number of famles. Subtracton of these subjects n the statstcal analyss dd not change the results. Fnally, we determned f our data were consstent wth the domnant nhertance pattern suggested by prevous reports. Our nferences on the mode of transmsson of the trat score 44 were based on condtonal nformaton for the selected cases and focused on the sbshps of subjects wth a score 44. Data were avalable for 23 chldren from subjects wth a score 44. Based on score phenotype, 2 of these chldren were affected (0.52), a proporton not sgnfcantly dfferent from the 0.50 expected for a fully penetrant domnant model, condtonal on one parent beng affected. We therefore dd not reject the hypothess of an autosomal-domnant transmsson. Dscusson Ths study s the frst to demonstrate the famlal clusterng of arteral lesons n FMD. Besdes the many case reports of renal FMD n twns or frstdegree relatves (manly ssters), the only prevous evdence for the exstence of famlal forms of renal FMD was provded by a large study n whch the dagnoss was suggested on the bass of medcal charts or ntervews and n whch relatves were consdered to carry the trat f they were known to have suffered varous condtons such as myocardal nfarcton or perpheral artery occlusve dsease. 7,3 6 We provde further evdence that FMD s a systemc, nhertable dsease, based on the use of echotrackng arteral score as a surrogate marker of renal FMD to characterze the genetc component of the dsease. In a prevous case control study of 70 renal FMD patents and control subjects matched for sex, age and blood pressure, we prevously showed that echotrackng score at the CCA was strongly assocated wth angographc phenotype. A score 43 was assocated wth an odds rato of 2.9 of havng renal FMD. Scorng was shown to be reproducble by the blnd, duplcate readng of 25 recordngs at 6-month ntervals, by three ndependent readers, provdng a correlaton coeffcent of A smlarly strngent protocol was appled to ths famlal study. The same traned techncans studed all subjects, usng the same procedures, wthn the same perod, and the same experenced readers determned scores after another thorough evaluaton of reproducblty. Thus, the strong and sgnfcant ncrease n CCA score observed for relatves of FMD patents probably dd not result from techncal bas. As famlal cases of medal FMD were prevously demonstrated to exhbt sgnfcantly more blateral and multfocal renal artery lesons than n sporadc cases, 6 the hypothess rased that famlal forms could represent a sub-entty of the dsease. We therefore focused on ther frst-degree relatve s arteral phenotype. FMD relatves had hghly abnormal CCA scores, wth a mean value almost twce that for controls matched for age and sex and smlar to that obtaned for establshed sporadc cases of FMD. Eleven of the 47 FMD relatves were known to be hypertensve. A systematc FMD screenng programme has been ntated n these relatves and should provde nsght nto the relatonshp between abnormal CCA score and renal FMD. Hypertenson per se does not seem to affect arteral score, as shown n our prevous study, n whch FMD cases were compared wth essental hypertenson patents matched for age and sex. 0 In addton,

7 the arteral score for ths lmted number of relatves was smlar for hypertensve and normotensve subjects (mean scores: 4.04 (2 6.83) vs 4.7 ( , P ¼ 0.4)). We therefore beleve that these results provde a strong ndcaton of arteral wall structure dsturbance n famles wth FMD. As the data provded by the sx pedgrees were nsuffcent to determne the mode of nhertance n a classcal segregaton analyss approach, we decded to compare mean scores n a generalzed lnear model, usng GEE-based estmates of regresson parameters and GEE-based parameter testng. Ths framework made t possble to take nto account the non-ndependence of score values between related ndvduals and to adjust for age and sex, despte the small effects of these factors. When several related ndvduals are ncluded n an analyss, neglectng the relatedness of the ndvduals tends to lead to msestmaton of the varance of the parameters, artfcally ncreasng or decreasng the sgnfcance of the test. In addton, GEEs make no assumptons about the dstrbuton of the trat and GEE estmates are robust to even severe dependence msspecfcaton. 2 For example, whereas the corrected test for score dfference between sporadc and famlal cases was not sgnfcant (P ¼ 0.07), a non-corrected test would have been sgnfcant (P ¼ 0.09 for a classcal lnear regresson parameter t-test). Conversely, the corrected test contrastng scores n relatves and famlal cases was sgnfcant (P ¼ 0.04), whereas a non-corrected test would not have been sgnfcant (P ¼ 0.8). Thus, famly structure modelng has a large mpact on the results obtaned, justfyng the use of a specfc statstcal approach. The selecton crtera appled n ths study, wth only relatves from famles wth at least two renal FMD cases ncluded, precluded classcal segregaton analyss, as too many data were mssng. Furthermore, the strength of selecton may have been even stronger because we cannot rule out the possblty that the sx famles agreeng to partcpate n ths extended study of relatves were more strongly affected than others or represented a partcular subset of FMD famles. Nonetheless, the hgher mean arteral score n relatves than n controls and the lower score n relatves than n famlal cases suggested a possble Mendelan dstrbuton of hgh scores n relatves. Based on condtonal nformaton for the selected cases n the famles, the pattern of segregaton of a score 44 n pedgrees was consstent wth an autosomaldomnant model of nhertance. Together the results of excess score n relatves, transmsson pattern and specfcty of the famlal FMD forms suggest a possble monogenc sub-entty of FMD assocated wth a hgh score. However, we cannot rule out that FMD s a heterogeneous multfactoral dsease wth a genetc component as suggested by Schevnk et al. 7 n cervcal artery dssectons. Evdence of arteral wall subclncal lesons n relatves of FMD pedgrees Perspectves Vascular remodelng may result from common alteratons, such as atheroscleross, or more specfc genetc vascular dsorders. IMT has been shown to be hertable and useful for mappng genes nfluencng ths trat. 8 In monogenc connectve tssue dseases (Marfan, Wllams Beuren and vascular Ehlers Danlos syndromes), precse characterzaton of the arteral phenotype has hghlghted the role of extracellular matrx sgnalng n vascular wall structure. 9 2 Our results, based on the use of an arteral score n renal FMD, provde strong evdence that FMD s a systemc nhertable dsease. The use of ths score as a surrogate trat for genetc lnkage studes wll requre ts valdaton n a larger number of famles. Moreover, the comparson between relatves scores of sporadc cases wth asymptomatc relatves of famlal cases could be proposed prevously to renforce the hypothess of a domnant mode of nhertance of the trat. Ths study also has clncal mplcatons. A score 44 n a relatve of a famlal FMD patent should lead the physcan to suspect renal FMD. We have shown that the specfcty and senstvty of carotd score are n the range of gold standards for the detecton of renal FMD n selected patents. 0,22,23 Prospectve evaluaton, usng ths score, would therefore be proposed as the determnaton of ths score s a non-nvasve test that could be used to dentfy patents lkely to have renal FMD. A complete dagnostc procedure n hypertensve What s known about ths topc K Medal renal artery FMD s a rare, non-atherosclerotc, nonnflammatory vascular dsease wth stenoses and saccular aneurysms. It may lead to renovascular hypertenson when stenoses are severe. K We have prevously shown that medal FMD may present as a famlal dsease n about 6% of cases. It has also been suggested that FMD s transmtted as an autosomal-domnant dsease wth ncomplete penetrance and varable clncal symptoms. K In a prevous study, we demonstrated that an elevated echotrackng score at the common carotd artery ste was strongly assocated (OR ¼ 2.9) wth sporadc medal FMD patents compared wth matched control subjects. What ths study adds K In ths study, we perform a segregaton analyss n sx famles, treatng arteral score as a dchotomous trat and usng a GEE approach, whch takes nto account the clusterng of data n famles. K We found evdence of arteral wall subclncal lesons n relatves of FMD pedgrees. The threshold was optmzed usng ROC curves and we found that dstrbuton of score 44 was consstent wth autosomal-domnant transmsson of the trat. K We provde here further evdence that FMD may be a systemc, nhertable dsease, based on the use of echotrackng arteral score as a surrogate marker of renal FMD to characterze the genetc component of the dsease. Abbrevatons: FMD, fbromuscular dysplasa; GEE, generalzed estmatng equaton; OR, odds rato; ROC, recever operatng characterstc. 399

8 400 ndvduals related to patents wth renal FMD, regardless of arteral score, could serve as the frst step n such an evaluaton. It remans unclear how normotensve relatves wth hgh echotrackng scores should be nvestgated, because subclncal renal FMD lesons are known to predspose the subject to early hypertenson. 24,25 Conflct of Interest None. Acknowledgements Ths study was sponsored by funds from INSERM (Insttut Natonal de la Santé et de la Recherche Médcale), Assstance Publque - Hôptaux de Pars Assocaton Naturala and Bologa, Agence Natonale pour la Recherche (ANR) and from the Programme Natonal de Recherche Cardovasculare (PNRC). Jérôme Perdu holds grants from the Fondaton pour la Recherche Médcale (FRM), the Fond d Études et de Recherche du Corps Médcal (FERCM) of Assstance Publque Hôptaux de Pars, the Socété Françase d Hypertenson Artérelle (SFHTA) and receved the Socété Françase de Cardologe (SFC) and Pfzer laboratores Award. 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