American Journal of Respiratory and Critical Care Medicine

Rationale: Activin A receptor type II-like kinase-1 (ACVRL1, also known as ALK1) mutation is a cause of hereditary hemorrhagic telangiectasia (HHT) and/or heritable pulmonary arterial hypertension (PAH).

Objectives: To describe the characteristics of patients with PAH carrying an ACVRL1 mutation.

Methods: We reviewed clinical, functional, and hemodynamic characteristics of 32 patients with PAH carrying an ACVRL1 mutation, corresponding to 9 patients from the French PAH Network and 23 from literature analysis. These cases were compared with 370 patients from the French PAH Network (93 with a bone morphogenetic protein receptor type 2 [BMPR2] mutation and 277 considered as idiopathic cases without identified mutation). Distribution of mutations in the ACVRL1 gene in patients with PAH was compared with the HHT Mutation Database.

Measurements and Main Results: At diagnosis, ACVRL1 mutation carriers were significantly younger (21.8 ± 16.7 yr) than BMPR2 mutation carriers and noncarriers (35.7 ± 14.9 and 47.6 ± 16.3 yr, respectively; P < 0.0001). In seven of the nine patients from the French PAH Network, PAH diagnosis preceded manifestations of HHT. ACVRL1 mutation carriers had better hemodynamic status at diagnosis, but none responded to acute vasodilator challenge and they had shorter survival when compared with other patients with PAH despite similar use of specific therapies. ACVRL1 mutations in exon 10 were more frequently observed in patients with PAH, as compared with what was observed in the HHT Mutation Database (33.3 vs. 5%; P < 0.0001).

Conclusions: ACVRL1 mutation carriers were characterized by a younger age at PAH diagnosis. Despite less severe initial hemodynamics and similar management, these patients had worse prognosis compared with other patients with PAH, suggesting more rapid disease progression.

Scientific Knowledge on the Subject

Patients with pulmonary arterial hypertension (PAH) carrying a bone morphogenetic protein receptor type 2 (BMPR2) mutation present approximately 10 years earlier than noncarriers and have a more severe hemodynamic compromise at diagnosis. Mutations in the activin A receptor type II-like kinase-1 (ACVRL1) gene are also recognized as a cause of heritable PAH. However, the influence of these mutations on clinical outcomes is unknown.

What This Study Adds to the Field

ACVRL1 mutation carriers are characterized by a younger age at PAH diagnosis. Despite a less severe initial hemodynamic compromise and similar management approach, these patients have a worse prognosis compared with other patients with PAH, suggesting more rapid disease progression.

Pulmonary arterial hypertension (PAH) is a severe disease affecting small pulmonary arteries, with progressive remodeling leading to elevated pulmonary vascular resistance and right ventricular failure (1, 2). PAH may occur in a number of different clinical contexts (3, 4). Idiopathic PAH corresponds to sporadic disease, without any family history of PAH or known triggering factor. When PAH occurs in a familial context, germline mutations in the bone morphogenetic protein receptor type 2 (BMPR2) gene are detected in approximately 70% of cases (510). BMPR2 mutations can also be detected in 3.5 to 40% of apparently sporadic cases (58, 11). The term “heritable” PAH has been proposed to describe these genetic forms of the disease (4, 6, 7, 1214).

Hereditary hemorrhagic telangiectasia (HHT) is characterized by mucocutaneous telangiectases, recurrent epistaxes, and macroscopic arteriovenous malformations, particularly in the pulmonary, hepatic, and cerebral circulation. When present, pulmonary arteriovenous malformations may create clinically significant right-to-left shunts, causing hypoxemia, paradoxical embolism, stroke, and cerebral abscesses (1520). In patients with HHT, postcapillary pulmonary hypertension may develop as a consequence of a hyperkinetic state, resulting in high cardiac output heart failure. However, HHT is also associated with a precapillary pattern of pulmonary hypertension that is histologically indistinguishable from idiopathic PAH (20, 21).

HHT is inherited in an autosomal dominant fashion with late-onset penetrance and nearly complete penetrance (97%) by the age of 60 years (22). Several genes have been implicated in the pathogenesis of HHT, including activin receptor-like kinase-1 (ACVRL1 or ALK1) located on chromosome 12, endoglin on chromosome 9, MADH4 (encoding the protein mothers against decapentaplegic homologue 4 [SMAD4], mutations of which also lead to juvenile polyposis), and two new loci (HHT3 and HHT4) mapped on chromosomes 5 and 7 (20, 23, 24). Data from several case series indicate that ACVRL1 mutations may predispose to PAH (21, 2528). In addition, rare cases of PAH in endoglin mutation patients have been reported, further supporting the probable involvement of the transforming growth factor (TGF)-β signaling pathway in the pathophysiology of both PAH and HHT (25, 27, 29).

Accumulated evidence indicates that patients with PAH carrying a BMPR2 mutation present approximately 10 years earlier than noncarriers, with more severely compromised hemodynamic status at diagnosis, and are less likely to respond to acute vasodilator testing (6, 7, 30). We hypothesized that mutated ACVRL1 status might be associated with distinct PAH phenotypes, as compared with patients with PAH without ACVRL1 mutation. To test this hypothesis, the French PAH Network obtained data on consecutive patients displaying PAH in whom point mutations and large size rearrangements of BMPR2 and ACVRL1 were screened for, and reviewed data in the literature for patients with PAH carrying an ACVRL1 mutation. Clinical, functional, and hemodynamic characteristics were compared between patients with PAH carrying an ACVRL1 mutation, patients carrying a BMPR2 mutation, and patients with PAH considered to be idiopathic and who were noncarriers of either a BMPR2 or ACVRL1 mutation.

Patients

We reviewed data from all patients with PAH considered to be idiopathic and patients with a family history of PAH, who were tested for BMPR2 and ACVRL1 mutations, seen in the French PAH Network (Université Paris-Sud 11, Hôpital Antoine-Béclère, Clamart, France) between January 1, 2004 and April 1, 2009. In accordance with the guidelines of the American College of Chest Physicians (31), patients tested for BMPR2 or ACVRL1 mutations signed written informed consent and underwent genetic counseling. A diagnosis of PAH was defined by hemodynamic measurement during right-heart catheterization (see below). Manifestations of HHT were screened and reported in patients with PAH carrying an ACVRL1 mutation. Patients with a family history of PAH without evidence of either BMPR2 or ACVRL1 mutation (n = 18) were excluded from the analysis to limit the risk of misclassification. All clinical characteristics at PAH diagnosis and follow-up were stored in the Registry of the French PAH Network (32). This registry was set up in agreement with French bioethics laws (French Commission Nationale de l'Informatique et des Libertés), and patients gave their consent to be included (7, 32). Additional detail is provided in the online supplement.

Hemodynamic Measurements and 6-Minute Walk Distance

PAH was defined as a mean pulmonary arterial pressure equal to or exceeding 25 mm Hg associated with a normal pulmonary capillary wedge pressure. Hemodynamic evaluation by right-heart catheterization was performed at baseline in all subjects according to our previously described protocol (33, 34). A nonencouraged 6-minute walk test was performed according to American Thoracic Society recommendations (35). Additional detail is provided in the online supplement.

Screening of Point Mutations and Large Rearrangements of ACVRL1 and BMPR2 Genes

Human genomic DNA was prepared from whole blood samples. Amplification of the entire coding sequence and intronic junctions of the ACVRL1 and BMPR2 genes was performed on 50 ng of genomic DNA from each individual. Genetic variation of the BMPR2 sequence was detected as previously described (7). Genetic variation of ACVRL1 was assayed by polymerase chain reaction and sequencing. The SALSA multiplex ligation-dependent probe amplification (MLPA) P093 HHT probemix kit (MRC-Holland BV, Amsterdam, The Netherlands) was used to screen for rearrangements of one or more exons of the ACVRL1 and BMPR2 genes. Additional description of the method is provided in the online supplement.

Literature Review

We performed a MEDLINE (National Library of Medicine, Bethesda, MD) search for PAH in patients carrying an ACVRL1/ALK1 mutation in articles published in the English language until April 2009. We recorded all data from patients with PAH carrying an ACVRL1 mutation reported in the literature. Individual clinical, functional, and hemodynamic characteristics from patients with PAH carrying an ACVRL1 mutation were available in five studies (21, 2527, 36) and ACVRL1 mutation status for patients with PAH were reported in six studies (21, 2528, 36). The distribution and frequency of mutations in the ACVRL1 gene in patients with PAH were compared with ACVRL1 mutations reported in the HHT Mutation Database (http://www.hhtmutation.org) on August 1, 2008, after analysis of the literature and exclusion of ACVRL1 mutations exclusively reported in patients with PAH.

Statistical Analysis

We compared demographic and clinical features between ACVRL1 mutation carriers, BMPR2 mutation carriers, and ACVRL1/BMPR2 mutation noncarriers by chi square test, Fisher's exact test, Kruskal-Wallis test, or analysis of variance followed by Fisher's protected least significant difference test, as appropriate. A P value less than 0.05 was considered to indicate statistical significance.

Patient Population

Between January 1, 2004, and April 1, 2009, all patients with PAH considered to be idiopathic and patients with a family history of PAH underwent genetic counseling and were offered BMPR2 and ACVRL1 screening. During this period, 388 patients were seen, 379 patients had genetic testing (98%), and 8 patients declined genetic testing. We identified 277 BMPR2/ACVRL1 mutation noncarriers, 93 BMPR2 mutation carriers, and 9 ACVRL1 mutation carriers (Figure 1).

Characteristics of French PAH Network Patients Carrying an ACVRL1 Mutation

The nine patients with PAH carrying an ACVRL1 mutation were identified in seven different families. Six cases had not been described previously whereas three have been reported (21, 37) (Figure 1). Family trees of six families are presented in Figure 2. No familial data were available for family 1 (adoption).

Clinical, functional, and hemodynamic characteristics of the study population are presented in Table 1. Clinical manifestations of HHT, age at diagnosis of PAH and HHT, and age at death are presented in Table 2. As observed in patients with PAH considered as idiopathic or in patients with a family history of PAH, we observed a female predominance in ACVRL1 mutation carriers who developed PAH (female-to-male ratio, 3.5). In four of nine patients, PAH was diagnosed before HHT, and two patients developed PAH without any clinical manifestations of HHT. Diagnoses of PAH and HHT were made at the same time in one patient. A personal HHT history was known before PAH diagnosis in only one patient. Epistaxes, telangiectases, and arteriovenous malformations were the most frequent manifestations of HHT observed in these patients. A familial PAH history was present in only one of the seven families reported (family 5). Patients were considered for PAH-specific therapy according to guidelines, but two of them died before initiation of this therapy (Table 3). In the nine patients with PAH and carrying an ACVRL1 mutation, overall mortality was worse than in BMPR2 mutation carriers or BMPR2/ACVRL1 mutation noncarriers (P < 0.01) (Figure 3); the cause of death was directly related to PAH in all patients (Table 3).

TABLE 1. CLINICAL, FUNCTIONAL, AND HEMODYNAMIC CHARACTERISTICS OF ACVRL1 MUTATION CARRIERS FROM THE FRENCH PULMONARY ARTERIAL HYPERTENSION NETWORK



Patient


1
2
3
4
5A
5B
6
7
Mean ± SD
Age at PAH diagnosis, yr33.229.540.4284.28.1115
NYHA functional classIIIIIIIIIIIIIIIIIIIIII
6-MWD, m315412455380307N/AN/A572407 ± 99
mPAP, mm Hg5450517061.239826158 ± 13
RAP, mm Hg205413118138 ± 6
PCWP, mm Hg84N/AN/A910158 ± 6
CO, L/min3.03.8N/A2.93.14.31.36.73.6 ± 1.7
CI, L/min/m21.82.46.01.45.64.63.03.93.6 ± 1.7
PVRi, mm Hg/L/min/m226.319.3N/AN/A9.36.326.714.415.4 ± 9.0
TPRi, mm Hg/L/min/m230.821.08.548.910.98.527.115.621.4 ± 13.9
Sv̄O2, %576881N/AN/AN/A567968 ± 12
Hemoglobin, g/dl13.51313.917.513.513.8N/AN/A14.2 ± 1.6
Acute vasodilator response
No
No
No
No
No
No
No
No
All negative

Definition of abbreviations: 6-MWD = 6-minute walk distance; CI = cardiac index; CO = cardiac output; mPAP = mean pulmonary artery pressure; N/A = not available at PAH diagnosis; NYHA = New York Heart Association; PAH = pulmonary arterial hypertension; PCWP = pulmonary capillary wedge pressure; PVRi = indexed pulmonary vascular resistance; RAP = right atrial pressure; Sv̄O2 = mixed venous oxygen saturation; TPRi = indexed total pulmonary resistance.

TABLE 2. AGE AT FIRST SYMPTOMS AND DIAGNOSIS OF PULMONARY ARTERIAL HYPERTENSION AND HEREDITARY HEMORRHAGIC TELANGIECTASIA




Patient

Sex

Age at PAH Diagnosis (yr)

Family History of PAH

Family History of HHT

HHT Manifestations

Age at HHT Diagnosis (yr)

Age at Death (yr)
French PAH Network1F33.2N/AN/AAVMs (pulmonary, ovarian, hepatic)33.239.3
2F29.5NoYesAVMs (pulmonary hepatic)31.331.5
Telangiectases
Epistaxes
3F40.4NoYesAVMs (splenic, hepatic)37.8
Epistaxes
4F28NoYesN/A32.733
5AF4.2YesYesEpistaxes10.1
5BM8.1YesYesTelangiectases12.1
Epistaxes
5CF1.1YesYesN/AN/A1.1
6F1NoYesNo (postmortem diagnosis)1.1
7M15NoYesNo
Trembath and colleagues (21)F1-III1M6YesYesNo7
F1-III2M1.5YesYesNo2
F1-III3F1.5YesYesTelangiectasesN/A9
Epistaxes
F2M29NoYesTelangiectasesN/A46
Epistaxes
F3-II1F45YesYesAVMs (pulmonary)N/A50
Telangiectases
Epistaxes
F3-II4F31YesYesTelangiectasesN/A34
Harrison and colleagues (25)7685F51NoNoNo54
7340F50NoYesTelangiectasesN/A
Epistaxes
7242F39NoYesAVMs (pulmonary)N/A
Telangiectases
Epistaxes
7253F19NoYesTelangiectasesN/AN/A
Epistaxes
8261F39YesYesTelangiectasesN/A
Epistaxes
7682F17NoYesNo18
8259F27NoYesTelangiectasesN/A
Epistaxes
7252F21NoYesTelangiectasesN/A
Epistaxes
7214M46NoNoTelangiectasesN/A
Epistaxes
Abdalla and colleagues (26)60F8YesYesTelangiectasesN/A
Epistaxes
82M0.4NoYesTelangiectasesN/A29
Epistaxes
91F43NoYesAVMs (hepatic, gastrointestinal)N/A51
Telangiectases
Epistaxes
100F18NoYesAVMs (pulmonary, hepatic, gastrointestinal)N/A20
Telangiectases
Epistaxes
Harrison and colleagues (27)7912F1.7NoNoNo
Smoot and colleagues (36)K1F4YesYesAVMs (pulmonary)N/A
Epistaxes
K2F16NoYesAVMs (pulmonary)N/A
Telangiectases
Epistaxes
K3F17NoYesAVMs (pulmonary)N/A
Telangiectases






Epistaxes


Definition of abbreviations: AVMs = arteriovenous malformations; F = female; HHT = hereditary hemorrhagic telangiectasia; M = male; N/A = not available; PAH = pulmonary arterial hypertension.

TABLE 3. FOLLOW-UP OF FRENCH PAH NETWORK PATIENTS WITH PULMONARY ARTERIAL HYPERTENSION CARRYING AN ACVRL1 MUTATION


Patient

PAH Therapy

Follow-up (months after diagnosis)

Cause of Death
1EpoprostenolDeath at Month 73Right heart failure
2Bosentan plus iloprostDeath at Month 24Rupture of PAVM
3Bosentan plus sildenafilAlive at Month 51
4EproprostenolDeath at Month 59Right heart failure
5AAtrioseptostomyAlive at Month 81
Epoprostenol plus bosentan
5BBosentan plus epoprostenolAlive at Month 59
5CNone: sudden death before initiation of PAH therapyDeath during the first monthRight heart failure
6None: sudden death before initiation of PAH therapyDeath at Month 2Right heart failure
7
Bosentan
Alive at Month 9

Definition of abbreviation: PAH = pulmonary arterial hypertension.

Characteristics of French PAH Network Patients Carrying or Not Carrying a BMPR2 Mutation

Outcome data relating to 223 patients with PAH from the French PAH Network, corresponding to 68 BMPR2 mutation carriers and 155 BMPR2/ACVRL1 mutation noncarriers, have previously been published by Sztrymf and colleagues (7). As of April 1, 2009, this series had been expanded to 379 patients with PAH, corresponding to 9 ACVRL1 mutation carriers, 93 BMPR2 mutations carriers, and 277 BMPR2/ACVRL1 mutation noncarriers. A mutation was detected in 47 of 65 families (72.3%) with at least two cases of confirmed PAH, corresponding to 44 of 65 (67.7%) BMPR2 mutations and 3 of 65 (4.6%) ACVRL1 mutations. In those considered to have idiopathic PAH, 49 of 332 (14.8%) patients carried a BMPR2 mutation and 6 of 332 (1.8%) carried an ACVRL1 mutation (Figure 4). As previously demonstrated, we confirmed in this larger series that BMPR2 mutation carriers were younger at diagnosis and at death (P < 0.002) (Figure 5). At diagnosis, BMPR2 mutation carriers were more severely compromised in hemodynamic status, with a lower cardiac index and mixed venous oxygen saturation (Sv̄O2) and higher mean pulmonary arterial pressure and indexed pulmonary vascular resistance, as compared with BMPR2/ACVRL1 mutation noncarriers (all P < 0.02) (Table 4).

TABLE 4. CLINICAL, FUNCTIONAL, AND HEMODYNAMIC CHARACTERISTICS AT DIAGNOSIS OF PULMONARY ARTERIAL HYPERTENSION




ACVRL1 Mutation Carriers (n = 32)

BMPR2 Mutation Carriers (n = 93)

BMPR2/ACVRL1 Mutation Noncarriers (n = 277)
Age at diagnosis, yr (mean ± SD)21.8 ± 16.7*35.7 ± 14.9*47.6 ± 16.3
Sex, female/male (ratio)25/7 (3.6)60/33 (1.8)182/95 (1.9)
6-MWD, m407 ± 99346 ± 100340 ± 114
mPAP, mm Hg60 ± 1763 ± 13*56 ± 14
RAP, mm Hg8 ± 68 ± 58 ± 5
PCWP, mm Hg9 ± 48 ± 38 ± 3
CI, L/min/m23.04 ± 1.332.11 ± 0.64*2.50 ± 0.71
PVRi, mm Hg/L/min/m219.0 ± 10.023.8 ± 12.8§20.6 ± 9.0
Sv̄O2, %66 ± 1359 ± 963 ± 10
Acute vasodilator responders, %
0/23
1/91
33/258

Definition of abbreviations: ACVRL1 = activin A receptor type II-like kinase-1; BMPR2 = bone morphogenetic protein receptor type 2; 6-MWD= 6-minute walk distance; CI = cardiac index; mPAP = mean pulmonary artery pressure; PCWP = pulmonary capillary wedge pressure; PVRi = indexed pulmonary vascular resistance; RAP = right atrial pressure; Sv̄O2 = mixed venous oxygen saturation.

Results are expressed as means ± SD.

*P < 0.0001 compared with BMPR2/ACVRL1 mutation noncarriers.

P < 0.0001 compared with BMPR2 mutation carriers.

P < 0.002 compared with BMPR2/ACVRL1 mutation noncarriers.

§P < 0.02 compared with BMPR2/ACVRL1 mutation noncarriers.

P < 0.05 compared with BMPR2 mutation carriers.

P < 0.005 compared with BMPR2/ACVRL1 mutation noncarriers.

Literature Search

A literature search identified 23 additional patients with PAH carrying an ACVRL1 mutation, with individual data in 20 different families (Figure 1) (21, 25, 36). Age at diagnosis of PAH, history of familial PAH, clinical manifestations of HHT, and age at death for ACVRL1 mutation carriers (n = 32) are reported in Table 2.

Clinical, functional, and hemodynamic characteristics of the 32 ACVRL1 mutation carriers from the French PAH Network (n = 9) and the literature search (n = 23) were compared with the characteristics of 93 BMPR2 mutations carriers and 277 BMPR2/ACVRL1 mutation noncarriers. At diagnosis, ACVRL1 mutation carriers were significantly younger (21.8 ± 16.7 yr) than BMPR2 mutation carriers and noncarriers (35.7 ± 14.9 and 47.6 ± 16.3 yr, respectively; P < 0.0001) (Figure 5). Age at death was lower in ACVRL1 and BMPR2 mutation carriers compared with noncarriers (26.6 ± 18.7, 35.2 ± 15.7, and 48.5 ± 17.5 yr, respectively; P < 0.0019) (Figure 5). Hemodynamic characteristics at diagnosis were less severe in ACVRL1 mutation carriers, as compared with BMPR2 mutation carriers, and were broadly similar to those observed in noncarriers (Table 4). In patients with PAH and who were carrying an ACVRL1 mutation, cardiac index was significantly higher as compared with BMPR2 mutation carriers (all P < 0.0001). No acute vasodilator responder was observed in our series or reported in the literature among ACVRL1 mutation carriers.

ACVRL1 Mutations in Patients with PAH

Fujiwara and colleagues reported five other patients with PAH with an ACVRL1 mutation (28). Thus, 36 patients with PAH carrying an ACVRL1 mutation were identified in 32 different families in our series (n = 8) and in the literature search (n = 28) (21, 2528, 36). In the context of PAH, we report 27 different ACVRL1 exonic mutations. All mutations are described in Table 5. In our series of nine patients with PAH, we identified four ACVRL1 mutations that were not previously reported: c.1280A > T (p.Asp427Val); c.1388delG (p.Gly463AlafsX2); c.602A > G (p.Gln201Arg); and c.1324G > A (p.Val442Met).

TABLE 5. DETAILS OF ACVRL1 MUTATIONS




Patient

Mutation Location

Mutation Category

Nucleotide Change

Amino Acid Change
French PAH Network1Exon 2Frameshiftc.37delCp.Leu13CysfsX2
2Exon 9Missensec.1280A > Tp.Asp427Val
3Exon 10Frameshiftc.1388delGp.Gly463AlafsX2
4Exon 10Nonsensec.1468C > Tp.Gln490X
5AExon 10Missensec.1450C > Tp.Arg484Trp
5BExon 10Missensec.1450C > Tp.Arg484Trp
6Exon 5Missensec.602A > Gp.Gln201Arg
7Exon 9Missensec.1324G > Ap.Val442Met
Trembath and colleagues (21)F1-III1Exon 10MissenseN/Ap.Arg484Trp
F1-III2Exon 10MissenseN/Ap.Arg484Trp
F1-III3Exon 10MissenseN/Ap.Arg484Trp
F2Exon 8MissenseN/Ap.Arg411Trp
F3-II1Exon 6DeletionN/Ap.254delAsp
F3-II4Exon 6DeletionN/Ap.254delAsp
Harrison and colleagues (25)7685Exon 5Missensec.536A > Cp.Asp179Ala
7340Exon 6Missensec.632G > Ap.Gly211Asp
7242Exon 7Missensec.1031G > Ap.Cys344Tyr
7253Exon 7Missensec.1031G > Ap.Cys344Tyr
8261Exon 8Missensec.1120C > Tp.Arg374Trp
7682Exon 8Missensec.1121G > Ap.Arg374Gln
8259Exon 8Missensec.1196G > Cp.Trp399Ser
7252Exon 8Missensec.1232G > Ap.Arg411Gln
7214Exon 10Missensec.1460A > Cp.Lys487Thr
Abdalla and colleagues (26)60Exon 10Insertionc.1450C > T, 1450-1451insGp.Arg484TrpfsX493
82Exon 10Nonsensec.1435C > Tp.Arg479X
91Exon 8Missensec.1120C > Tp.Arg374Trp
100Exon 10Nonsensec.1385C > Gp.Ser462X
Harrison and colleagues (27)7912Exon 10Missensec.1451G > Ap.Arg484Gln
Fujiwara and colleagues (28)4Exon 10Missensec.1436G > Ap.Arg479Gln
9Exon 8Missensec.1142T > Cp.Leu381Pro
18Exon 10Missensec.1451G > Ap.Arg484Gln
20Exon 9Missensec.1270C > Ap.Pro424Thr
21Exon 7Missensec.936C > Gp.His312Gln
Smoot and colleagues (36)K1Exon 7Missensec.T818Cp.Leu273Pro
K2Exon 8Missensec.C1055Ap.Ala352Asp

K3
Exon 8
Missense
c.C1055A
p.Ala352Asp

n = 36 patients in 32 different families.

The mutation nomenclature follows current guidelines as recommended by the Human Genome Variation Society (www.hgvs.org/mutnomen/). Protein consequence for frameshift mutation: “the position of the stop in the new reading frame is calculated starting at the first amino acid that is changed by the frame shift, and ending at the first stop codon.”

In the HHT Mutation Database (http://www.hhtmutation.org), we found 264 ACVRL1 mutations in patients displaying HHT but no reported PAH. These corresponded to 242 exonic and 22 intronic mutations (with 5.3% splice defects). Twelve ACVRL1 mutations (5% exonic mutations) were present in exon 10, of which 7 were localized in the nonactivating non–down-regulating (NANDOR) box (3%) in patients with HHT with no reported PAH (Table 6 and Figure 6). In patients with PAH carrying an ACVRL1 mutation, we found 9 different mutations (in 14 patients with PAH from 11 distinct families) in exon 10. This represents 33.3% of reported ACVRL1 mutations in patients with PAH, of which six (22.2%) were localized in the NANDOR box (Table 6 and Figure 6). Thus, compared with patients with HHT, ACVRL1 mutations in exon 10 were more frequently observed in patients with PAH than in patients with HHT without reported PAH (P < 0.0001).

TABLE 6. DISTRIBUTION OF THE VARIOUS ACVRL1 MUTATIONS IN PATIENTS WITH PULMONARY ARTERIAL HYPERTENSION* AND IN PATIENTS WITH HEREDITARY HEMORRHAGIC TELANGIECTASIA WITHOUT REPORTED PULMONARY ARTERIAL HYPERTENSION


Exon

PAH patients with ACVRL1 Mutation*

HHT without Reported PAH
21 (3.7%)2 (0.8%)
30 (0%)61 (25.2%)
40 (0%)22 (9.1%)
52 (7.4%)9 (3.7%)
62 (7.4%)20 (8.3%)
73 (11.1%)53 (21.9%)
87 (25.9%)40 (16.5%)
93 (11.1%)23 (9.5%)
10
9 (33.3%)
12 (5.0%)

Definition of abbreviations: ACVRL1 = activin A receptor type II-like kinase-1; HHT = hereditary hemorrhagic telangiectasia; PAH = pulmonary arterial hypertension.

*n = 27 different mutations in 36 patients.

Mutation Database: http://www.hhtmutation.org (n = 242 exonic mutations).

In this study, clinical, functional, and hemodynamic characteristics of ACVRL1 mutation carriers, identified from the French PAH Network and from previously published cases, were compared with patients with PAH considered to be idiopathic or with patients with PAH carrying a BMPR2 mutation. We demonstrated that age at PAH diagnosis and age at death of ACVRL1 mutation carriers were significantly lower as compared with BMPR2/ACVRL1 mutation noncarriers. In this series, we confirmed that ACVRL1 mutation carriers may develop severe PAH without any clinical evidence of HHT. Our results on the distribution and frequency of mutations in the ACVRL1 gene argue for a predominance of mutations in exon 10 in ACVRL1 mutation carriers who develop PAH, as compared with ACVRL1 mutation carriers with isolated HHT. The association between mutations in the ACVRL1 gene and the development of severe PAH further supports the hypothesis that disruption of the TGF-β pathway is central to the development of PAH (5, 38). Furthermore, as previously described by Sztrymf and colleagues (7), we confirm that BMPR2 mutation carriers were younger at diagnosis and at death, with more severely compromised hemodynamic status at diagnosis than BMPR2/ACVRL1 mutation noncarriers. Interestingly, in our cohort, a BMPR2 mutation was found in 44 patients (67.7%) with a family history of PAH, and in 49 patients (14.8%) without a family history of PAH. On the basis of our findings, systematic genetic counseling for idiopathic patients with PAH even in the absence of a family history of PAH should be considered.

Our data indicate that ACVRL1 mutation carriers are significantly younger at PAH diagnosis, as compared with BMPR2 mutation carriers and noncarriers. More than one third of patients with PAH carrying an ACVRL1 mutation were children or young teenagers (<16 yr). All causes of death were directly related to PAH, and, even if their baseline hemodynamic characteristics were less severe compared with those of BMPR2 mutation carriers, age at death among patients with PAH who were carriers of an ACVRL1 mutation was broadly similar to that of BMPR2 mutation carriers and significantly less than that of patients without BMPR2 or ACVRL1 mutations.

Sztrymf and colleagues demonstrated that BMPR2 mutation carriers and noncarriers had similar overall survival, but that BMPR2 mutation carriers were more likely to undergo lung transplantation with a significantly shorter time to death or lung transplantation (7). Because lung transplantation is the only remaining therapeutic option for patients with severe PAH who cannot be managed medically, time to death or lung transplantation is an accepted indicator of disease severity in this patient population. Therefore, these data suggest that BMPR2 mutation carriers have more severe disease, which is in accordance with the observation that this patient population is more severely compromised hemodynamically compared with noncarriers. However, none of the ACVRL1 mutation carriers underwent lung transplantation, partly because of the shortage of donor lungs for pediatric PAH but also because of physician reluctance to propose lung transplantation in patients with evidence of HHT (including extrapulmonary arteriovenous malformations). Thus, to avoid a biased analysis due to different surgical treatment options in different subgroups we decided to study only overall survival in the present analysis. This confirmed similar overall survival in BMPR2 mutation carriers and noncarriers, but ACVRL1 mutation carriers had significantly worse overall survival (Figure 3).

Patients with ACVRL1 mutations may also have HHT (diagnosed either before or after PAH), which has a known association with comorbidities including visceral hemorrhage. In patients from the French Pulmonary Hypertension Referral Center, anemia was excluded as a cause of worse prognosis in our population. In addition, the hypothesis of a worse prognosis directly or indirectly related to comorbidities of HHT was not supported by the extensive analysis of the patients of the French Pulmonary Hypertension Referral Center. Indeed, ACVRL1 mutation carriers with PAH clinically deteriorated more quickly and they ultimately died of pulmonary hypertension–related causes, indicating that these individuals had more rapid progression, as compared with other patients with PAH, despite similar therapeutic approaches. Only one patient died of a partly HHT-related complication, namely rupture of a pulmonary arteriovenous malformation, but this was due at least in part to the severity of underlying PAH (37).

These observations suggest more rapid disease evolution in ACVRL1 mutation carriers compared with BMPR2/ACVRL1 mutation noncarriers, as observed in BMPR2 mutation carriers (7). As previously reported in patients with PAH carrying a BMPR2 mutation (7, 30), acute vasodilator response was uncommon in heritable PAH and no acute responders were identified among patients with PAH carrying an ACVRL1 mutation.

HHT is an autosomal dominant disease with nearly complete penetrance by the age of 60 years, with a female-to-male ratio of 1:1 (15). Interestingly, as previously demonstrated in patients with PAH considered to be idiopathic and in patients with a family history of PAH, we report a female predominance among patients with PAH carrying an ACVRL1 mutation. It has been demonstrated that in HHT, pulmonary arteriovenous malformations and possibly hepatic involvement and cerebral hemorrhage are more frequent in women (16, 39). It was hypothesized that such female predominance may reflect an effect of female sex hormones on the remodeling observed in HHT vasculature or relate to hemodynamic changes during pregnancy (16).

ACVRL1 mutation carriers from the French PAH Network had a diagnosis of PAH preceding HHT diagnosis in the majority of cases (seven of nine cases). Epistaxes, telangiectases, and arteriovenous malformations were the most frequent signs of HHT observed in the course of the disease. History of familial PAH was present in only one of the seven families reported. This is in agreement with previous reports indicating that signs of PAH may be the first or indeed the only manifestation in ACVRL1 mutation carriers (25, 27, 28). For instance, Fujiwara and colleagues found 5 ACVRL1 mutations in 21 pediatric patients with PAH without any sign of HHT (28). In addition, Harrison and colleagues reported a case of a patient with PAH carrying an ACVRL1 mutation, with severe PAH diagnosed at the age of 51 years, an age that is considered to have nearly complete penetrance of HHT (25). This patient died at the age of 54 years and necropsy found no pathological features of HHT (25). Furthermore, some characteristic signs of HHT, and particularly epistaxes, are nonspecific and relatively common, and usually not spontaneously reported by the patient or not considered as informative by the medical team in the context of PAH. Therefore, better awareness of the possibility of HHT in patients with PAH should lead to a systematic search for clinical features of HHT in this patient population. In addition, a detailed family history and careful examination of first-degree relatives for subtle manifestations of HHT are required, although phenotypic variability and the possibility of de novo mutation mean that the diagnosis cannot be excluded even if no abnormalities are identified within the family.

The observation that ACVRL1 mutation carriers develop PAH earlier may illustrate the constitutive susceptibility conferred by the mutation on the course of the disease. The formation of an heteromeric complex with BMPR-II and ALK1 has been proposed (5, 21, 40, 41) and this model could at least in part explain why subjects carrying either a BMPR2 or ACVRL1 mutation are predisposed to PAH. Furthermore, this complex may be associated with an accessory receptor such as endoglin, and heretofore, only four cases of PAH associated with an endoglin mutation have been reported in the literature (25, 27, 29). Thus, patients with endoglin mutation seem to be at lower risk of developing PAH compared with ACVRL1 mutation carriers. ACVRL1 haploinsufficiency may lead to a pulmonary vascular status that predisposes to the development of PAH. Interestingly, our data confirm that ACVRL1 mutation carriers with PAH have a predominance of mutations in exon 10 and particularly in the NANDOR box. Of note, the NANDOR box, located from codon 479 to 489, is necessary for regulation of TGF-β signaling (25, 27, 42). Thus, mutations in this region may critically affect the regulation of the TGF-β signalization pathway. Dysregulation of this pathway may promote pulmonary endothelial and/or smooth muscle cell dysfunction and proliferation characteristic of PAH (21). The high frequency of mutations in exon 10 underscores the need for increasing PAH awareness in this subgroup of patients. However, there are several reported patients with HHT carrying a mutation in the NANDOR box in exon 10, but with no evidence of PAH. Furthermore, most ACVRL1 mutation carriers in a given family will not develop PAH, indicating that an ACVRL1 mutation is not sufficient to induce PAH. These results reinforce the hypothesis that an additional genetic or environmental hit is necessary in order to trigger a pulmonary vascular disease in predisposed subjects (43, 44).

Our study included literature-based subjects, which could induce a bias in the analysis of ACVRL1 mutation carriers. However, all published cases of ACVRL1 mutation carriers in the literature and all BMPR2 mutation carriers and noncarriers from the French PAH Network were reported in our study. Moreover, age at diagnosis and age at death of ACVRL1 mutation carriers from the French PAH Network and from the literature search were similar (age at diagnosis: 18.5 ± 16.0 and 23.1 ± 17.2, respectively [P = 0.50]; age at death: 21.2 ± 18.6 and 29.1 ± 19.2, respectively [P = 0.45]). Furthermore, to avoid a potential survival bias because of different management strategies adopted for the cases from the literature, our survival analysis focused only on patients from the French Pulmonary Hypertension Referral center, where all patients with PAH have a similar therapeutic approach irrespective of the genetic or familial background.

Another possible limitation of this study relates to familial clustering. Indeed, familial clustering could impact our data in terms of both gene and environmental interactions that may alter disease expression beyond that of a single gene mutation. However, the majority of PAH cases we studied were the only reported cases from their families and familial clustering represented only a minority of reported cases. In the French PAH Network, six of nine ACVRL1 mutation carriers were the only PAH cases reported in their families, with three belonging to the same family. In the literature search, 18 of 23 ACVRL1 mutation carriers were the only family members with PAH, with two families having 3 and 2 cases reported, respectively. Thus the majority of cases were the only reported PAH in their families and familial clustering represented a minority of reported cases. A similar proportion of multiple reported cases from single families was identified in BMPR2 mutation carriers (24 of 93 had an affected family member, 26%). On the basis of these findings, it was concluded that a familial influence was similar in ACVRL1 and BMPR2 mutation carriers, and we have thus not performed any family-based approach in our analysis.

In conclusion, our study served to describe clinical characteristics, hemodynamic features, and outcomes for patients with PAH carrying an ACVRL1 mutation. Of note, these patients had a poor clinical outcome, and patients with PAH carrying an ACVRL1 mutation were characterized by a younger age at diagnosis and death, as compared with patients with PAH without BMPR2 and ACVRL1 mutation. Although PAH is a rare complication in ACVRL1 mutation carriers, our data emphasize the poor prognosis of this patient population, and argues in favor of screening for clinical signs of PAH in such patients to detect PAH earlier when medical management may be more efficacious. Furthermore, because PAH may develop in ACVRL1 mutation carriers without obvious manifestations of HHT, a detailed family history and a careful examination of patients with PAH and first-degree relatives for stigmata of HHT may help detect these patients.

The authors thank the patients, their families, and healthcare providers for agreeing to collaborate.

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Correspondence and requests for reprints should be addressed to David Montani, M.D., Université Paris-Sud, Centre National de Référence de l'Hypertension Pulmonaire Sévère, Service de Pneumologie et Réanimation Respiratoire, Hôpital Antoine Béclère, 157, Rue de la Porte de Trivaux, 92140 Clamart, France. E-mail:

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