Journal of Human Hypertension (2007) 21, 393–400 & 2007 Nature Publishing Group All rights reserved 0950-9240/07 $30.00 www.nature.com/jhh ORIGINAL ARTICLE Inheritance of arterial lesions in renal fibromuscular dysplasia

J Perdu1,2, P Boutouyrie3,4,5,10, C Bourgain6,7,10, N Stern1,8, B Laloux4, E Bozec4, M Azizi3,8, C Bonaiti-Pellie´6,7, P-F Plouin2,3,9, S Laurent3,4,5, A-P Gimenez-Roqueplo1,2,3 and X Jeunemaitre1,2,3 1AP-HP, Department of Genetics, Hoˆpital Europe´en Georges Pompidou, Paris, France; 2INSERM, Unit 772, Colle`ge de France, Paris, France; 3Faculte´ de Me´decine, Universite´ Paris Descartes, Paris, France; 4AP-HP, Department of Pharmacology, Hoˆpital Europe´en Georges Pompidou, Paris, France; 5INSERM, Unit 337, Paris, France; 6INSERM, Unit 535, Villejuif, France; 7Universite´ Paris-Sud, Villejuif, France; 8AP-HP, Hoˆpital Europe´en Georges Pompidou, Clinical Investigation Center CIC9201, Paris, France and 9AP-HP, Department of Hypertension, Hoˆpital Europe´en Georges Pompidou, Paris, France

We have previously shown that patients with renal cases had also a high carotid score (4.17), very fibromuscular dysplasia (FMD) have asymptomatic significantly higher than that of controls (2.52, Po10À5) carotid lesions and that familial forms may occur. The even though lower than the corresponding index FMD objective of this study was to test whether carotid cases (4.81, P ¼ 0.01). Segregation analysis showed that lesions could be detected in relatives of familial cases. 52% of the descendants of subjects with a score 44 had High-resolution echotracking of the carotid artery was a score 44, a proportion consistent with autosomal- performed in 47 relatives of 13 cases from six families. dominant transmission of the trait. Altogether these This non-invasive investigation led to a semiquantitative results strengthen the hypothesis of renal FMD being arterial score that was compared with that obtained for a systemic arterial disease and argue for a familial 47 controls matched for age and sex and that for 125 resemblance that may be due to a major genetic effect. sporadic cases. Familial resemblance was tested by The carotid score obtained by high-resolution echo- using a generalized estimating equation approach tracking may provide a non-invasive surrogate marker taking into account the clustering of scores in families. for renal FMD of potential value for use in linkage As expected, FMD cases had a significantly higher score strategies on large pedigrees. than controls (4.02 vs 2.52, Po10À5). Familial cases were Journal of Human Hypertension (2007) 21, 393–400. not significantly different from sporadic cases. Of doi:10.1038/sj.jhh.1002156; published online 1 March 2007 interest, the 47 apparently healthy relatives of familial

Keywords: genetics; fibromuscular dysplasia; renovascular; echotracking; arterial stiffness; generalized estimating equation approach

Introduction and saccular aneurysms. In medial FMD, renal artery lesions usually present as multiple, multi- Renal artery fibromuscular dysplasia (FMD) is a focal stenoses with intervening aneurysms causing rare, non-atherosclerotic, non-inflammatory vascu- a ‘string of beads’ appearance, whereas unifocal lar disease of truncal or branch kidney arteries, of stenoses are usually associated with intimal FMD. If unknown pathophysiology. In medial FMD, the renal artery stenoses are severe, FMD may result in most prevalent form of FMD, pathologic examina- renovascular hypertension and, if dissection occurs, tion shows successive areas of parietal thickening in renal infarction.1,2 (corresponding to medial hyperplasia) and dilata- Medial FMD occurs predominantly in middle- tion (following disruption of internal elastic lami- aged Caucasian women, and a number of risk factors na). These arterial alterations may lead to stenoses have been identified in this group of women: smoking habits, oral contraceptive intake and genetic factors.1,3–5 Medial FMD may present as a Correspondence: Dr J Perdu, Department of Genetics, Hoˆpital familial disease, defined as the presence of angio- Europe´en Georges Pompidou, 20-40, rue Leblanc, 75908 Paris graphically documented FMD in at least two first- Cedex 15, France. degree relatives.6 It has also been suggested that E-mail: [email protected] 10These authors contributed equally to this work. FMD is transmitted as an autosomal-dominant Received 18 September 2006; revised 28 November 2006; disease with incomplete penetrance and variable accepted 24 December 2006; published online 1 March 2007 clinical symptoms.7,8 Evidence of arterial wall subclinical lesions in relatives of FMD pedigrees J Perdu et al 394 Identifying the genes responsible for FMD is Methods therefore an appropriate strategy for investigation of the pathophysiology of this disease. However, this Patients and subjects approach requires the identification of a reliable Fourteen (6.1%) of the 228 FMD patients referred to phenotype for separating unaffected and affected the Hypertension Unit of our institution since 1986 subjects, even in the absence of symptoms. Renal were considered to correspond to familial cases artery duplex sonography may be not sensitive because at least one of the first-degree relatives of enough, especially in cases of non-stenotic lesions1 these patients (the sister in 13 cases) also had and computed tomographic or magnetic resonance angiographically proven renal FMD. Three of the 14 angiography have a poor specificity in patients with families concerned were impossible to trace, one FMD.9 Renal angiography is an invasive test and could not be studied for geographical reasons and would be unethical to use for the characterization two consisted of two FMD cases with no living of normotensive members of a pedigree. We recently relatives. The relatives of the FMD cases in the eight showed, with carotid artery high-resolution echo- remaining families were asked to participate in a tracking techniques, that FMD is actually a systemic clinical research protocol based on a routine clinical disease and that subclinical lesions of the common examination, together with arterial echotracking and carotid artery (CCA) wall are commonly found in blood sampling for DNA extraction and analysis. patients with renal artery medial FMD. An arterial These eight families contained 113 eligible relatives, phenotypic score of 2 (normal) to 7 (highly abnor- of whom 26 refused to participate, 23 could not be mal) has been shown to be strongly associated with contacted and 17 were willing to participate but FMD.10 could not because of geographical constraints. The In this study, we used this score as a surrogate final analysis included 47 Caucasian relatives from marker for renal FMD phenotype, in the character- six pedigrees studied in detail (Figure 1). These ization of first-degree relatives of affected subjects. subjects were compared with 47 normotensive We selected pedigrees containing at least two Caucasian control subjects matched for age and patients with angiographically proven renal FMD. sex, who were recruited during the same period We showed, using a generalized estimating equation among the medical staff members and their families. (GEE) approach, that relatives of renal FMD familial Control subjects known to be hypertensive were cases have significantly higher arterial score values excluded. They underwent the same procedures, than matched controls, suggestive of the presence of carried out by the same trained technicians (EB, BL), subclinical arterial lesions. We performed a segrega- as FMD patients and relatives. The study was tion analysis in six families, treating arterial score approved by our institutional ethics committee as a dichotomous trait. We found that ‘score 44’ was (Approval CCPPRB Paris-Cochin # RBM 00–028) a heritable trait with an autosomal-dominant mode and all subjects gave written informed consent. As of inheritance. previously described, for a part of this cohort

FMD 004 FMD 008 FMD 143 ? ? ? ND ND ND ND ND ND

? ? ND ND 4.90 ND 6.75 4.16 4.50 6.00 4.08 5.17 3.70 3.08 3.75 4.00

ND 5.50 3.67 3.71 3.94 5.80 2.00 4.37 2.66 4.00 4.00 3.50 5.00

? FMD 125 ? FMD 074 ?? 4.50 4.25 2.34 4.04 ND ND ND ND ND ND

FMD 018 ? 5.75 4.21 3.66 4.83 ND ND 3.00 4.00 ND

7.00 4.75 5.00 5.16 ND 4.90 4.83 4.80 4.91 5.55 5.91

5.00 2.00 4.83 4.33 4.50 4.58 3.25 4.66 4.33 3.50 4.16 2.08 5.16 2.16 6.83 2.33 2.00

FMD-YES HT-YES HT-NO? HT-UNK Figure 1 Structure of the six renal FMD families. Arterial phenotypic score is presented beneath each subject icon. HT: hypertension; UNK: unknown; FMD: renal fibromuscular dysplasia.

Journal of Human Hypertension Evidence of arterial wall subclinical lesions in relatives of FMD pedigrees J Perdu et al 395 (N ¼ 104), each FMD patient underwent a standar- included in the regression are independent (con- dized medical evaluation.6 The procedures followed trols, sporadic cases), this is strictly equivalent to a were in accordance with institutional guidelines. Student’s t-test for comparing mean values of the score in the two groups, adjusted for the covariates. Echotracking measurements When several related individuals are included This investigation was performed in a controlled (multiple cases or multiple relatives from a parti- environment kept at þ 22711C, after the subject had cular family), tests should account for it. Indeed, remained in a recumbent position for 15 min. Right as we suspect a familial correlation of the score, CCA was studied 2 cm beneath the carotid bifurca- neglecting the relatedness of the individuals would tion, with a 7.5 MHz linear array ultrasound probe misestimate the variance of the regression para- (Pie Medical 350, Maastricht, The Netherlands) meters and artificially either increase or decrease coupled with an echotracking system (Walltrack the significance of the tests. To account for subject System, Pie Medical), as described previously.11 We relatedness, we used a GEE approach.12 Briefly, let Yi be the vector of score values for all ni first checked inter-observer reproducibility; the T results were then read blind by two observers (JP, individuals in family i, Yi ¼ðYi;1; ...; Yi; niÞ where PB), and the arterial phenotypic score was deter- Yi;1 is the score of individual 1 from family i.LetXi mined as described previously (Table 1, Figure 2).10 be the matrix of the K covariates included in the 1 y k k For each patient, relative and control, we recorded model for family i, Xi ¼ (Xi , ,Xi ) and Xi ¼ ðXk ...Xk ÞT where X k is the value of the Kth several B-mode images and RF signals graphs, to i;1 i;ni i;ni prevent image-associated reading errors. Even if covariate for the ni individual of family i. only the measurements on right CCA are presented b ¼ðb0;ÁÁÁ; bj;ÁÁÁ; bkÞ is the vector of the K regression in this work, our echotracking protocol system- parameters. For individual j in family i, our model is: Y ¼ b þ b X 1 þÁÁÁþb X k þ e . EðY Þ¼m ¼ atically included the examination of proximal P ij 0 1 i;j k i;j ij i i internal carotid artery and CCA 2 cm beneath the j ^ bjXi . The GEE estimator for b is b ¼ bifurcation on both sides. Moreover, presence of ÀjP ÀÁP 0 ~À1 À1 0 ~À1 ~ atherosclerotic plaques was systematically recorded i Xi Si XiÞ i Xi Si Yi where Si is the work- to avoid any artificial increase of the score. ing correlation matrix of Yi. Because we have no model for the familial dependence of the score, we Statistical analysis used the identity matrix as a workingP correlationP Comparisons of scores. Data were analysed in a ^ 0 À1 matrix in the calculation of b ¼ð Xi XiÞ ð XiYiÞ. generalized linear model framework. The arterial i i phenotypic score is regressed on covariates (sex, This corresponds to a linear regression analysis on age) and to compare scores between groups (familial independent observations where the clustering of vs sporadic cases, relatives vs controlsy), a binary data in families is preserved. variable discriminating the groups to be compared is An estimate for the variance of b^ robust to the added in the model. When all the individuals misspecification of the familial dependences of the score is ! À1 Table 1 Mode of calculation of carotid artery echotracking score X ^ 0 ~À1 varðbÞ¼ Xi Si Xi Type of abnormality Score i X ! X À1 B mode 0 ~À1 0 ~À1 Double-line normal pattern (normal blood-intima and 1 Xi Si ðyi À m^iÞðyi À m^iÞ Si Xi media-adventitia acoustic interfaces) i ! X Dotted pattern (discontinuous blood-intima acoustic 2 X À1 interface) 0 ~À1 Core pattern (discontinuous additional acoustic 3 Xi Si Xi interface between the two normal lines) i Triple signal pattern (continuous supernumerary 4 which, if the identity matrix is used for S~ ; can be acoustic interface between the two normal lines) i reduced to ! Radiofrequency signals X À1 Double signal (constant normal two-waved acoustic 1 ^ 0 varðbÞ¼ Xi Xi signal) 1 X ! ! Alternation of double and triple signal over 2 À1 successive acquisitions X X 0 0 0 Triple signal (constant three-wave signal 3 Xi ðYi À m^iÞðYi À m^iÞ Xi Xi Xi corresponding to an additional acoustic interface) i 1

Total (range 2–7) For each regression parameter bj we tested the null hypothesis.qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffibj ¼ 0, with a standard Student’s A given individual is characterized by B-mode score and radio- b^ b^ frequency signal score. The minimum score is 2, and the maximum t-test j varð jÞ where the robust variance is score is 7. used.

Journal of Human Hypertension Evidence of arterial wall subclinical lesions in relatives of FMD pedigrees J Perdu et al 396

Probe Radiofrequency signal

Two-dimensional study

Figure 2 Echotracking study showing a triple signal of the CCA wall in B-mode scan and in radio frequency mode. In normal arterial wall, ultrasound reflects off of two acoustic interfaces (blood-intima and media-adventitia), resulting in two reflected waves on RF graphs and a double-line pattern on the grey-scale image generated in two-dimensional mode. The detection of a permanent additional wave in RF mode (black arrow) and/or of a continuous supernumerary line in B-mode (white arrow) between the two normal lines is called ‘triple signal’. This pattern is observed in a high proportion of FMD patients, and the additional interface corresponds to histologic medial hyperplasia.

Mode of transmission. We investigated the mode of focal FMD was male. The clinical and radiological transmission of renal FMD, using the arterial score characteristics of the familial and sporadic cases as a surrogate marker, by converting the score into of renal FMD (Table 2) were consistent with a dichotomous trait, using an optimal threshold of published reports of female predominance and 4 to separate affected and unaffected individuals. moderate to severe hypertension. Familial cases We plotted receiver-operating characteristic curves, more frequently displayed bilateral and multi- which showed that a score 44 was associated with a focal lesions than did sporadic cases. Ten relatives maximum specificity of 97.8% and a sensitivity of were known to have hypertension (21%). Cardio- 65.9%. Only one control subject (2.1%) had a score vascular risk factors of the four groups are detailed 44. As familial cases were selected on the basis of in Table 2. there being at least two affected cases in the family, The distribution of arterial phenotypic scores for we could not run a classical segregation analysis the 13 probands and affected siblings of the six using the score as a trait. Instead, we based our pedigrees studied, the 125 sporadic cases, the 47 inference on the transmission pattern of the trait in relatives and their matched control subjects is offspring of selected cases. This approach is condi- summarized in Figure 3. For these 232 subjects, we tional on the information regarding the selected detected a robust effect of age ðb^age ¼ 0:02 with cases, and is thus unbiased even when families are P ¼ 6.6 Â 10À7), and a small but significant effect not selected at random. of sex (b^sex ¼ 0:28 and P ¼ 0.024) on arterial score. We therefore compared the scores in the different groups, using the following regression model: Results y ¼ b0 þ b1 age þ b2 sex þ b3 group, where group is a binary variable contrasting the two groups. The six FMD pedigrees contained two affected The mean scores obtained were 4.81, 4.02, 4.17 trios of sisters and four affected pairs (Figure 1). and 2.52 for familial cases, sporadic cases, relatives One of the affected trios had only one surviving first- of familial cases and controls, respectively. Table 3 degree relative, a brother, whereas the other five presents the regression parameters of the model kindreds provided 4–15 relatives spanning 2–3 used to compare scores between these groups. It also generations. Only one proband with typical multi- displays the P-value for the test of the null

Journal of Human Hypertension Evidence of arterial wall subclinical lesions in relatives of FMD pedigrees J Perdu et al 397 a 4 Familial FMD cases N = 13 b 15 FMD first degree relative N = 47

Mean = 4.81 Mean = 4.17 3 10

2 Number Number 5 1

0 0 2 3 4 5 6 7 2 3 4 5 6 7 Score Score

cd25 Sporadic FMD cases N = 125 30 Control subjects N = 47

25 20 Mean = 4.02 Mean = 2.52

20 15 15 Number Number 10 10

5 5

0 0 2 3 4 5 6 7 2 3 4 5 6 7 Score Score Figure 3 Arterial phenotypic score distribution for the 13 probands and affected sibs of the six affected families (a), their 47 relatives (b), 125 sporadic cases of renal FMD (c) and controls matched to the relatives (d).

Table 2 Clinical and radiological characteristics of Caucasian familial and sporadic FMD cases, relatives and controls

Sporadic cases Familial cases Relatives Controls (n ¼ 125) (n ¼ 13) (n ¼ 47) (n ¼ 47)

Age (years) 52.5714.8 56.0711.2 46.6716.3 46.1714.6 Sex (% female) 89.4 92.3 44.7 44.7 Bilateral renal FMD (%) 58.1 76.9 — — Multifocal lesions (%) 73.6 100 — — Systolic BP (mm Hg) 177.1732.0 186.3724.7 129.3716.7 127.2724.3 Diastolic BP (mm Hg) 104.8715.6 111.8721.1 76.279.1 74.2713.2 Hypertension (%) 100 100 21.0 0 BMI (kg/m2) 23.273.2 24.974.9 24.773.7 23.773.1 Smoking habit (%) 24.8 38.5 19.1 27.7 Dyslipidemia (%) 12.0 7.7 14.9 8.7 Diabetes (%) 1.6 7.7 8.5 0

Abbreviations: BMI, body mass index; BP, blood pressure (before any treatment in familial and sporadic cases); FMD, fibromuscular dysplasia. Data are expressed as mean7s.d.

hypothesis b3 ¼ 0, corresponding to the comparison significantly smaller than scores in relatives of mean scores adjusted for age and sex and (Po10À5). corrected for family clustering. Age differences between groups did not confound The scores of sporadic and familial cases differ the observed differences in scores. After splitting with statistically nonsignificant trends (P ¼ 0.07), the population according to the median of age of but both were significantly higher than in controls propositus, we performed an analysis of variance (Po10À5). Relatives had significantly lower scores including a population term (familial, relatives, than did familial cases (P ¼ 0.014), but these scores sporadic cases or controls), and an age term (below did not differ significantly from those obtained for and above median). Although this analysis con- sporadic cases (P ¼ 0.4). These results were not firmed higher scores in FMD patients, we did not intuitive when mean scores were compared (i.e. observe any influence of age, nor interaction with 4.81 vs 4.02, P ¼ 0.07; 4.81 vs 4.17, P ¼ 0.014), high- population term. lighting the importance of correcting for familial There was no indication that different levels of structure. Very interestingly, scores in controls are atherosclerosis could have affected our results. As

Journal of Human Hypertension Evidence of arterial wall subclinical lesions in relatives of FMD pedigrees J Perdu et al 398 Table 3 Regression of score on age, sex and group, using the GEE

Regression coefficient P-value

Groups (0 vs 1) Intercept b2 (s.d.) Age b1 (s.d.) Sex b2 (s.d.) Group b3 (s.d.) Group test b3 ¼ 0

Sporadic cases vs familial cases 2.88 (0.52) 0.02 (0.005) 0.38 (0.23) 0.73 (0.41) 0.07 Controls vs relatives 1.97 (0.56) 0.01 (0.009) À0.09 (0.34) 1.64 (0.30) o10À5 Relatives vs familial cases 3.18 (0.15) 0.02 (0.004) À0.07 (0.23) 0.52 (0.21) 0.014 Relatives vs sporadic cases 3.21 (0.36) 0.02 (0.005) À0.008 (0.22) À0.17 (0.21) 0.40 Controls vs familial cases 2.07 (0.69) 0.007 (0.014) 0.21 (0.45) 2.33 (0.45) o10À5 Controls vs sporadic cases 1.70 (0.31) 0.02 (0.005) À0.10 (0.20) 1.50 (0.18) o10À5

Abbreviations: GEE, generalized estimating equation; s.d., standard deviation.

Values of estimated regression parameters and associated s.d. and P-value of the t-test for group coefficient b3 ¼ 0. Model is y ¼ b0 þ b1ageþb2sexþb3group, where group is 0 or 1.

hypertension may have been correlated with in- have suffered various conditions such as myo- creased intima-media thickness (IMT), and possibly cardial infarction or peripheral artery occlusive with a falsely high score, we assessed the influence disease.7,13–16 We provide further evidence that of hypertension on the scores of relatives of familial FMD is a systemic, inheritable disease, based on cases (with the model: y ¼ a þ b1 age þ b2 sex þ the use of echotracking arterial score as a surrogate b3 HT). No significant effect was detected (P-value marker of renal FMD to characterize the genetic of b3 test ¼ 0.32). In addition, the four groups were component of the disease. not different concerning the incidence of smoking In a previous case–control study of 70 renal FMD habit and dyslipidemia as well as for their mean patients and control subjects matched for sex, age body mass index. Only, presence of diabetes and blood pressure, we previously showed that mellitus was more often present in familial cases echotracking score at the CCA was strongly asso- and relatives than in sporadic cases and control ciated with angiographic phenotype. A score 43 population (P ¼ 0.04, w2 test). Its higher frequency in was associated with an odds ratio of 12.9 of having FMD patients (7.5%) and their relatives (8.5%) is renal FMD. Scoring was shown to be reproducible probably a spurious finding observed because of the by the blind, duplicate reading of 25 recordings observation of a small number of families. Subtrac- at 6-month intervals, by three independent readers, tion of these subjects in the statistical analysis did providing a correlation coefficient of 0.9.10 A not change the results. similarly stringent protocol was applied to this Finally, we determined if our data were consistent familial study. The same trained technicians studied with the dominant inheritance pattern suggested by all subjects, using the same procedures, within the previous reports. Our inferences on the mode of same period, and the same experienced readers transmission of the trait ‘score 44’ were based on determined scores after another thorough evaluation conditional information for the selected cases and of reproducibility. Thus, the strong and significant focused on the sibships of subjects with a score 44. increase in CCA score observed for relatives of FMD Data were available for 23 children from subjects patients probably did not result from technical bias. with a score 44. Based on score phenotype, 12 of As familial cases of medial FMD were previously these children were affected (0.52), a proportion not demonstrated to exhibit significantly more bilateral significantly different from the 0.50 expected for and multifocal renal artery lesions than in sporadic a fully penetrant dominant model, conditional on one cases,6 the hypothesis raised that familial forms parent being affected. We therefore did not reject the could represent a sub-entity of the disease. We hypothesis of an autosomal-dominant transmission. therefore focused on their first-degree relative’s arterial phenotype. FMD relatives had highly abnor- mal CCA scores, with a mean value almost twice Discussion that for controls matched for age and sex and similar to that obtained for established sporadic cases of This study is the first to demonstrate the familial FMD. Eleven of the 47 FMD relatives were known clustering of arterial lesions in FMD. Besides the to be hypertensive. A systematic FMD screening many case reports of renal FMD in twins or first- programme has been initiated in these relatives degree relatives (mainly sisters), the only previous and should provide insight into the relationship evidence for the existence of familial forms of renal between abnormal CCA score and renal FMD. FMD was provided by a large study in which the Hypertension per se does not seem to affect arterial diagnosis was suggested on the basis of medical score, as shown in our previous study, in which charts or interviews and in which relatives were FMD cases were compared with essential hyperten- considered to carry the trait if they were known to sion patients matched for age and sex.10 In addition,

Journal of Human Hypertension Evidence of arterial wall subclinical lesions in relatives of FMD pedigrees J Perdu et al 399 the arterial score for this limited number of relatives Perspectives was similar for hypertensive and normotensive Vascular remodeling may result from common subjects (mean scores: 4.04 (2–6.83) vs 4.71 (3.71– alterations, such as atherosclerosis, or more specific 6.75, P ¼ 0.141)). We therefore believe that these genetic vascular disorders. IMT has been shown to results provide a strong indication of arterial wall be heritable and useful for mapping genes influen- structure disturbance in families with FMD. cing this trait.18 In monogenic connective tissue As the data provided by the six pedigrees were diseases (Marfan, Williams–Beuren and vascular insufficient to determine the mode of inheritance Ehlers–Danlos syndromes), precise characterization in a classical segregation analysis approach, we of the arterial phenotype has highlighted the role decided to compare mean scores in a generalized of extracellular matrix signaling in vascular wall linear model, using GEE-based estimates of regres- structure.19–21 Our results, based on the use of an sion parameters and GEE-based parameter testing. arterial score in renal FMD, provide strong evidence This framework made it possible to take into that FMD is a systemic inheritable disease. The use account the non-independence of score values of this score as a surrogate trait for genetic linkage between related individuals and to adjust for age studies will require its validation in a larger number and sex, despite the small effects of these factors. of families. Moreover, the comparison between When several related individuals are included in an relatives scores of sporadic cases with asymptomatic analysis, neglecting the relatedness of the indivi- relatives of familial cases could be proposed duals tends to lead to misestimation of the variance previously to reinforce the hypothesis of a dominant of the parameters, artificially increasing or decreas- mode of inheritance of the trait. ing the significance of the test. In addition, GEEs This study also has clinical implications. A score make no assumptions about the distribution of the 44 in a relative of a familial FMD patient should trait and GEE estimates are robust to even severe lead the physician to suspect renal FMD. We have dependence misspecification.12 For example, shown that the specificity and sensitivity of carotid whereas the corrected test for score difference score are in the range of gold standards for the between sporadic and familial cases was not detection of renal FMD in selected patients.10,22,23 significant (P ¼ 0.07), a non-corrected test would Prospective evaluation, using this score, would have been significant (P ¼ 0.019 for a classical linear therefore be proposed as the determination of this regression parameter t-test). Conversely, the cor- score is a non-invasive test that could be used to rected test contrasting scores in relatives and identify patients likely to have renal FMD. A familial cases was significant (P ¼ 0.014), whereas complete diagnostic procedure in hypertensive a non-corrected test would not have been significant (P ¼ 0.18). Thus, family structure modeling has a large impact on the results obtained, justifying the use of a specific statistical approach. What is known about this topic K Medial renal artery FMD is a rare, non-atherosclerotic, non- The selection criteria applied in this study, with inflammatory vascular disease with stenoses and saccular only relatives from families with at least two renal aneurysms. It may lead to renovascular hypertension when FMD cases included, precluded classical segrega- stenoses are severe. tion analysis, as too many data were missing. K We have previously shown that medial FMD may present as a Furthermore, the strength of selection may have familial disease in about 6% of cases. It has also been suggested that FMD is transmitted as an autosomal-dominant been even stronger because we cannot rule out the disease with incomplete penetrance and variable clinical possibility that the six families agreeing to partici- symptoms. pate in this extended study of relatives were more K In a previous study, we demonstrated that an elevated strongly affected than others or represented a echotracking score at the common carotid artery site was strongly associated (OR ¼ 12.9) with sporadic medial FMD particular subset of FMD families. Nonetheless, the patients compared with matched control subjects. higher mean arterial score in relatives than in controls and the lower score in relatives than in What this study adds familial cases suggested a possible Mendelian K In this study, we perform a segregation analysis in six distribution of high scores in relatives. Based on families, treating arterial score as a dichotomous trait and using a GEE approach, which takes into account the conditional information for the selected cases in the clustering of data in families. families, the pattern of segregation of a score 44 K We found evidence of arterial wall subclinical lesions in in pedigrees was consistent with an autosomal- relatives of FMD pedigrees. The threshold was optimized dominant model of inheritance. using ROC curves and we found that distribution of ‘score 44’ was consistent with autosomal-dominant transmission of Together the results of excess score in relatives, the trait. transmission pattern and specificity of the familial K We provide here further evidence that FMD may be a FMD forms suggest a possible monogenic sub-entity systemic, inheritable disease, based on the use of of FMD associated with a high score. echotracking arterial score as a surrogate marker of renal FMD However, we cannot rule out that FMD is a to characterize the genetic component of the disease. heterogeneous multifactorial disease with a genetic 17 Abbreviations: FMD, fibromuscular dysplasia; GEE, generalized component as suggested by Schievink et al. in estimating equation; OR, odds ratio; ROC, receiver operating char- cervical artery dissections. acteristic.

Journal of Human Hypertension Evidence of arterial wall subclinical lesions in relatives of FMD pedigrees J Perdu et al 400 individuals related to patients with renal FMD, tomographic angiography and magnetic resonance regardless of arterial score, could serve as the first angiography for diagnosing renal artery stenosis. Ann step in such an evaluation. It remains unclear how Intern Med 2004; 141: 674–682. normotensive relatives with high echotracking 10 Boutouyrie P, Gimenez-Roqueplo AP, Fine E, Laloux B, scores should be investigated, because subclinical Fiquet-Kempf B, Plouin PF et al. Evidence for carotid and radial artery wall subclinical lesions in renal FMD lesions are known to predispose the 24,25 renal fibromuscular dysplasia. J Hypertens 2003; 21: subject to early hypertension. 2287–2295. 11 Hoeks AP, Willekes C, Boutouyrie P, Brands PJ, Willigers JM, Reneman RN. Automated detection of Conflict of Interest local artery wall thickness based on M-line signal None. processing. Ultrasound Med Biol 1997; 23: 1017–1023. 12 Liang KY, Zeger SL. Longitudinal analysis using generalized linear models. Biometrika 1986; 73: 13–22. Acknowledgements 13 Major P, Genest J, Cartier P, Kuchel O. Hereditary fibromuscular dysplasia with renovascular hyperten- This study was sponsored by funds from INSERM sion. Ann Intern Med 1977; 86: 583. (Institut National de la Sante´ et de la Recherche 14 Morimoto S, Kuroda M, Uchida K, Funatsu T, Me´dicale), Assistance Publique - Hoˆpitaux de Paris Yamamoto I, Hashiba T et al. Occurrence of renovas- Association Naturalia and Biologia, Agence Natio- cular hypertension in two sisters. Nephron 1976; 17: nale pour la Recherche (ANR) and from the 314–320. Programme National de Recherche Cardiovasculaire 15 Bigazzi R, Bianchi S, Quilici N, Salvadori R, Baldari G. (PNRC). Je´roˆme Perdu holds grants from the Fonda- Bilateral fibromuscular dysplasia in identical twins. tion pour la Recherche Me´dicale (FRM), the Fond Am J Kidney Dis 1998; 32: E4. ´ 16 Halpern MH, Sanford HS, Viamonte Jr M. Penetrance d’Etudes et de Recherche du Corps Me´dical estimates and recurrence risks for fibromuscular (FERCM) of Assistance Publique – Hoˆpitaux de hyperplasia of the renal arteries. Acta Med Scand Paris, the Socie´te´ Franc¸aise d’Hypertension Arte´r- 1965; 194: 512–513. ielle (SFHTA) and received the Socie´te´ Franc¸aise 17 Schievink WI, Wijdicks EF, Michels VV, Vockley J, de Cardiologie (SFC) and Pfizer laboratories Award. Godfrey M. Heritable connective tissue disorders in We thank the technical staff of the laboratory of cervical artery dissections: a prospective study. Neu- Molecular Genetics and the Clinical Investigation rology 1998; 50: 1166–1169. 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