Clinical efficacy and safety of selexipag in children and young adults with idiopathic and heritable pulmonary arterial hypertension.

OBJECTIVE: This study aimed to investigate the safety, tolerability, and efficacy of selexipag in children and young adults with idiopathic and heritable pulmonary arterial hypertension. METHODS: This retrospective cohort study included clinical data from five children and six young adults with pulmonary arterial hypertension receiving selexipag as add-on therapy or as a transition from beraprost sodium or epoprostenol infusion therapy. Clinical efficacy was evaluated by measuring improvement in clinical variables from baseline, including hemodynamic parameters. RESULTS: Of the 11 patients, 6 were switched from beraprost sodium to selexipag and one paediatric patient transitioned from epoprostenol to selexipag. The median maintenance dose of selexipag in children was 80 µg/kg/day. In nine patients undergoing repeat catheterisation, statistically significant improvements were observed after the initiation of selexipag in terms of mean pulmonary arterial pressure (p < 0.01), pulmonary vascular resistance index (p < 0.05), and cardiac index (p < 0.01). None of the patients had clinical worsening after selexipag during follow-up, but one young adult patient discontinued treatment due to severe headache. The most common side effect profiles were headache, nausea, abdominal pain, jaw pain, myalgia, and diarrhoea. CONCLUSIONS: Selexipag may have a favourable safety profile and potential efficacy in children and young adults with pulmonary arterial hypertension.

Genetic and functional analyses of TBX4 reveal novel mechanisms underlying pulmonary arterial hypertension.

BACKGROUND: Pulmonary arterial hypertension (PAH) is a fatal disease, with approximately 10% of cases associated with genetic variants. Recent genetic studies have reported pathogenic variants in the TBX4 gene in patients with PAH, especially in patients with childhood-onset of the disease, but the pathogenesis of PAH caused by TBX4 variant has not been fully uncovered. METHODS: We analysed the TBX4 gene in 75 Japanese patients with sporadic or familial PAH using a PCR-based bidirectional sequencing method. Detected variants were evaluated using in silico analyses as well as in vitro analyses including luciferase assay, immunocytochemistry and chromatin immunoprecipitation (ChIP) whether they have altered function. We also analysed the function of TBX4 using mouse embryonic lung explants with inhibition of Tbx4 expression. RESULTS: Putative pathogenic variants were detected in three cases (4.0%). Our in vitro functional analyses revealed that TBX4 directly regulates the transcriptional activity of fibroblast growth factor 10 (FGF10), whereas the identified TBX4 variant proteins failed to activate the FGF10 gene because of disruption of nuclear localisation signal or poor DNA-binding affinity. Furthermore, ex vivo inhibition of Tbx4 resulted in insufficiency of lung morphogenesis along with specific downregulation of Tie2 and Kruppel-like factor 4 expression. CONCLUSION: Our results implicate variants in TBX4 as a genetic cause of PAH in a subset of the Japanese population. Variants in TBX4 may lead to PAH through insufficient lung morphogenesis by disrupting the TBX4-mediated direct regulation of FGF10 signalling and pulmonary vascular endothelial dysfunction involving PAH-related molecules.

Outcomes of idiopathic pulmonary arterial hypertension in Japanese children: a retrospective cohort study.

Recently, targeted therapy has been developed for idiopathic pulmonary arterial hypertension (IPAH). Studies evaluating the prognosis of IPAH have been conducted in adults. However, there is no nationwide survey of pediatric patients with IPAH regarding the long-term prognosis in Japan. Therefore, we investigated the clinical outcomes of Japanese pediatric patients with IPAH and risk factors for a poor prognosis. This multi-center, retrospective cohort study included pediatric patients with IPAH under the age of 15 years, who were gleaned from the nationwide network of Japanese Society of Pediatric Cardiology and Cardiac Surgery (JSPCCS). The questionnaire was sent to members of JSPCCS in 2015. Patients who were diagnosed with IPAH from 1994 to 2014 were included. The primary endpoint was death or lung transplantation. Ninety-five patients were finally enrolled. Both the mean age at diagnosis and the mean follow-up duration were 7 years. Ninety-five percent of patients had received targeted therapy for IPAH during follow-up. The overall 1, 3, 5, and 10-year event free rate, estimated using Kaplan-Meier survival estimate, was 96, 91, 83, and 74%, respectively. The prognosis was significantly poorer in patients with increased right ventricular systolic pressure (RVp), mean pulmonary artery pressure (mPAP) (≥ 52 mmHg), cardiothoracic ratio (≥ 55%), and levels of B-type natriuretic peptide (BNP) during follow-up (≥ 300 pg/mL) than in those without these parameters. In conclusion, in Japanese children with IPAH, the event-free rate for death or lung transplantation was found to be good. Greater RVp, mPAP, BNP levels during follow-up, and cardiothoracic ratio may be predictive indicators for a poor prognosis.

Role of BRCA1-associated protein (BRAP) variant in childhood pulmonary arterial hypertension.

Although mutations in several genes have been reported in pulmonary arterial hypertension (PAH), most of PAH cases do not carry these mutations. This study aimed to identify a novel cause of PAH. To determine the disease-causing variants, direct sequencing and multiplex ligation-dependent probe amplification were performed to analyze 18 families with multiple affected family members with PAH. In one of the 18 families with PAH, no disease-causing variants were found in any of BMPR2, ACVRL1, ENG, SMAD1/4/8, BMPR1B, NOTCH3, CAV1, or KCNK3. In this family, a female proband and her paternal aunt developed PAH in their childhood. Whole-exome next-generation sequencing was performed in the 2 PAH patients and the proband's healthy mother, and a BRCA1-associated protein (BRAP) gene variant, p.Arg554Leu, was identified in the 2 family members with PAH, but not in the proband's mother without PAH. Functional analyses were performed using human pulmonary arterial smooth muscle cells (hPASMCs). Knockdown of BRAP via small interfering RNA in hPASMCs induced p53 signaling pathway activation and decreased cell proliferation. Overexpression of either wild-type BRAP or p.Arg554Leu-BRAP cDNA constructs caused cell death confounding these studies, however we observed higher levels of p53 signaling inactivation and hPASMC proliferation in cells expressing p.Arg554Leu-BRAP compared to wild-type BRAP. In addition, p.Arg554Leu-BRAP induced decreased apoptosis of hPASMCs compared with wild-type BRAP. In conclusion, we have identified a novel variant of BRAP in a Japanese family with PAH and our results suggest it could have a gain-of-function. This study sheds light on new mechanism of PAH pathogenesis.

Detection of Pediatric Pulmonary Arterial Hypertension by School Electrocardiography Mass Screening.

Rationale: To detect pulmonary arterial hypertension (PAH) at any early stage is a promising approach to optimize the outcome. Objectives: To investigate the impact of school ECG-based screening on detecting idiopathic or heritable (I/H)-PAH in the general pediatric population. Methods: This was a nationwide survey of patients with I/H-PAH newly diagnosed at 3 months to 18 years of age in Japan during 2005-2012. Measurements and Main Results: Eighty-seven eligible patients (age range, 1-16 yr) were recruited. Among 68 (78%) patients diagnosed at greater than or equal to 6 years of age (the age of the first ECG-based screening), 28 (41%) were detected by the ECG-based screening (screening group) and 40 (59%) were recognized by their symptoms (n = 37) or coincidental occasions (n = 3; nonscreening group). In the screening group, the proportion of patients in World Health Organization functional class I/II at diagnosis was higher (96% vs. 60%; P < 0.001), plasma brain natriuretic peptide level was lower (149 ± 290 vs. 398 ± 559 pg/ml; P = 0.045), and 6-minute-walk distance was longer (420 ± 109 vs. 327 ± 104 m; P < 0.001) than the nonscreening group, despite similar values in mean pulmonary artery pressure (58 ± 17 vs. 61 ± 17 mm Hg; P = 0.42) and pulmonary vascular resistance index (18 ± 8 vs. 21 ± 11 Wood units ⋅ m2; P = 0.24) between groups. The proportion of patients on intravenous epoprostenol at the final visit was lower in the screening group than the nonscreening group (14% vs. 50; P = 0.004). Conclusions: These findings suggest that the ECG-based screening detects a unique subpopulation of pediatric patients with I/H-PAH that is associated with already established pulmonary hypertension but without obvious right heart failure and warrants investigating the prognostic significance of this system.

Clinical Effects of Syncope on Disease Severity and Adverse Outcomes in Children with Idiopathic and Heritable Pulmonary Arterial Hypertension.

Syncope is more common in children with idiopathic pulmonary arterial hypertension (PAH) than in adults with PAH. Although syncope is associated with a poor prognosis in adult PAH, the clinical effects of syncopal events on disease severity and outcome in children have not been carefully investigated. This study assessed the prevalence of syncope in pediatric PAH and examined its clinical, hemodynamic, and prognostic importance. This retrospective study assessed clinical data, including syncope status, from 78 children (37 girls) with idiopathic and heritable PAH (median age at diagnosis, 11 years). Patients were classified as syncopal or non-syncopal, and clinical data from the two groups were compared. The primary outcome was a composite of lung transplantation and cardiac mortality. Overall, 31 (38%) children had a history of syncope at presentation. Median age at diagnosis, sex ratio, brain natriuretic peptide level, and 6-min walk distance at diagnosis did not differ between groups. The hemodynamic parameters of initial right heart catheterization were similar between the syncope and non-syncope group (mean pulmonary artery pressure, 67 versus 71 mm Hg; cardiac index, 2.9 versus 2.9 l/min/m2, respectively). There was not significantly difference in event-free survival rate between two groups. Although syncopal events are common in children with PAH, our findings suggest that syncope may not be correlated with disease severity or outcome in pediatric PAH.

Correction to: Clinical Effects of Syncope on Disease Severity and Adverse Outcomes in Children with Idiopathic and Heritable Pulmonary Arterial Hypertension.

The original version of this article unfortunately contained a mistake in the author name. The co-author name should be Hiroyuki Matsuura instead of Horoyuki Matsuura. The original article has been corrected.

Clinical Impact of Main Pulmonary Artery Dilatation on Outcome in Pediatric Idiopathic and Heritable Pulmonary Arterial Hypertension.

BACKGROUND: Few studies have investigated the clinical impact of pulmonary artery (PA) dilatation on outcomes in pediatric pulmonary arterial hypertension (PAH).Methods and Results:This study investigated the clinical outcomes of idiopathic or heritable PAH in 66 children aged <18 years at diagnosis. Main PA/thorax (MPA/T) ratio was measured on chest radiography in PAH patients. Patients were divided into 2 groups based on MPA/T ratio, and compared with a control group of 166 age- and gender-matched healthy children. Group A had higher MPA/T ratio than normal, and group B had normal MPA/T ratio. Composite outcomes included cardiac death, lung transplantation, and hospitalization due to heart failure. Group A consisted of 27 patients and group B, 39 patients. At diagnosis, group A had significantly higher brain natriuretic peptide (BNP), cardiothoracic ratio, PA pressure, and pulmonary vascular resistance index compared with group B. The number of patients with New York Heart Association (NYHA) functional class III and IV was significantly higher in group A than in group B. Cumulative event-free survival rate was significantly lower in group A. CONCLUSIONS: MPA dilatation correlated with BNP, NYHA functional class, and hemodynamics with regard to disease severity, and may be a potential prognostic factor in pediatric idiopathic and heritable PAH.

Effect of treatment with epoprostenol and endothelin receptor antagonists on the development of thyrotoxicosis in patients with pulmonary arterial hypertension.

Thyroid disease is known to be associated with pulmonary arterial hypertension (PAH). We investigated the prevalence of thyroid disease in patients with idiopathic PAH (IPAH) or heritable PAH (HPAH), and the factors affecting the pathogenesis of thyroid disease. We retrospectively evaluated 59 patients with IPAH or HPAH who had been diagnosed with PAH before the age of 20 years. Thyrotoxicosis was detected in 12 of the 59 patients (6 patients with Graves' disease, 3 with hashitoxicosis, and 3 with silent thyroiditis) after the start of PAH treatment. The proportion of patients who received epoprostenol in the thyrotoxicosis group was significantly higher than that in the euthyroid group (12/12 vs. 27/47, p=0.015). In the 39 patients treated with epoprostenol, the proportion of patients who received combination therapy with epoprostenol and an endothelin receptor antagonist (ERA) in the thyrotoxicosis group was significantly lower than that in the euthyroid group (5/12 vs. 23/27, p=0.016). Logistic regression analysis revealed that thyrotoxicosis development was significantly associated with administration of epoprostenol (odds ratio [OR] 8.22, 95% confidence interval [CI] 1.26-53.74, p=0.028) and non-administration of ERA (OR 5.33, 95% CI 1.29-22.06, p=0.021). The prevalence of thyrotoxicosis was high in patients with IPAH or HPAH. The onset of thyrotoxicosis might be promoted by epoprostenol and inhibited by ERA.

Efficacy and Safety of an Orally Administered Selective Prostacyclin Receptor Agonist, Selexipag, in Japanese Patients With Pulmonary Arterial Hypertension.

BACKGROUND: Selexipag is an orally available prostacyclin receptor (IP receptor) agonist with a non-prostanoid structure. In this open-label Phase II trial, the efficacy and safety of selexipag in Japanese patients with pulmonary arterial hypertension (PAH) is examined.Methods and Results:Selexipag was administered at 200 µg twice daily and titrated up to 1,600 µg by increments of 200 µg in 37 subjects to reach the individual maximum tolerated dose. At 16 weeks, in 33 patients comprising the per-protocol set, the pulmonary vascular resistance (PVR; primary endpoint) decreased from 683.2±237.3 to 560.3±238.7 dyn·s/cm5(P<0.0001). For the secondary endpoint, the 6-min walk distance (6MWD) increased from 445.0±102.2 to 459.1±112.8 m (P=0.0324); World Health Organization functional class improved in 4 patients (12.1%), and was maintained in 29 patients (87.9%). A decrease in PVR was also shown in patients treated with selexipag, on top of a phosphodiesterase inhibitor and endothelin receptor antagonist. Most of the commonly reported adverse events were consistent with those reported for other PGI2formulations. Thirty-four patients attained the individual maximum tolerated dose (maintenance dose). CONCLUSIONS: The efficacy and tolerability of selexipag in Japanese PAH patients was confirmed by improvement in pulmonary hemodynamics, exercise capacity, symptoms. Selexipag is an efficacious treatment option for Japanese PAH patients. (Trial registration: JAPIC Clinical Trials Information [JapicCTI-111532].).

Pulmonary Arterial Capacitance Index Is a Strong Predictor for Adverse Outcome in Children with Idiopathic and Heritable Pulmonary Arterial Hypertension.

OBJECTIVES: To evaluate the clinical utility of pulmonary artery capacitance index (PACi) in the assessment of disease severity and prognostic value in children with idiopathic and heritable pulmonary arterial hypertension (PAH). STUDY DESIGN: PACi is defined as the ratio of stroke volume index over pulmonary pulse pressure. A retrospective study was performed to compare PACi, brain natriuretic peptide (BNP), 6-minute walk distance, New York Heart association (NYHA) functional class, and adverse outcomes (hospitalization due to heart failure, lung transplantation, and cardiac mortality) in 72 Japanese children (10 ± 3.6 years) with idiopathic and heritable PAH. RESULTS: PACi had significant correlations with pulmonary vascular resistance index (r =-0.73, P < .0001), BNP levels (r = -0.40, P = .0008), and 6-minute walk distance (r = 0.57, P < .05). Statistically significant differences in PACi were observed between NYHA functional class II vs combined III and IV (median; 1.1 vs 0.6 mL/mm Hg/m2, respectively, P < .05). There were 25 of 72 (35%) children who had an adverse event including initiation of hospitalization due to heart failure, lung transplantation, and death. Cumulative event-free survival rate was significantly lower when PACi was <0.85 mL/mm Hg/m2 (log-rank test, P < .0001). CONCLUSIONS: PACi correlated with BNP and NYHA functional class and may serve as a strong prognostic marker in children with idiopathic and heritable PAH.

Sildenafil reduces pulmonary vascular resistance in single ventricular physiology.

BACKGROUND: High pulmonary vascular resistance (PVR) may be a risk factor for early and late mortality in both Glen shunt and Fontan operation patients. Furthermore, PVR may increase long after the Fontan operation. Whether pulmonary vasodilators such as phosphodiesterase 5 inhibitors can decrease PVR in patients with single ventricular physiology remains undetermined. METHODS AND RESULTS: This was a prospective, multicenter study. Patients with single ventricular physiology who have a PVR index higher than 2.5 Wood units·ãŽ¡ (WU) were enrolled. Cardiac catheterization was performed before and after administration of sildenafil in all patients. After the Fontan operation, a six minute walk test (6MWT) was also performed. A total of 42 patients were enrolled. PVR was significantly decreased in each stage of single ventricular physiology after sildenafil administration: from 4.3±1.5WU to 2.1±0.6WU (p<0.01) in patients before a Glenn shunt, from 3.2±0.5WU to 1.6±0.6WU (p<0.001) in patients after a Glenn shunt, and from 3.9±1.7WU to 2.3±0.8WU (p<0.001) in patients after Fontan. In patients after Fontan, the 6MWT increased from 416±74m to 485±72m (p<0.01), and NYHA functional class improved significantly (p<0.05) after sildenafil administration. No major side effects were observed in any patients. CONCLUSIONS: Sildenafil reduced PVR in patients with single ventricle physiology. Sildenafil increased exercise capacity and improved NYHA functional class in patients after a Fontan operation. This implies that pulmonary vasodilation is a potential therapeutic target in selected patients with elevated PVR with single ventricle physiology. Long-term clinical significance warrants further study.

Mutations of NOTCH3 in childhood pulmonary arterial hypertension.

Mutations of BMPR2 and other TGF-ß superfamily genes have been reported in pulmonary arterial hypertension (PAH). However, 60-90% of idiopathic PAH cases have no mutations in these genes. Recently, the expression of NOTCH3 was shown to be increased in the pulmonary artery smooth muscle cells of PAH patients. We sought to investigate NOTCH3 and its target genes in PAH patients and clarify the role of NOTCH3 signaling. We screened for mutations in NOTCH3, HES1, and HES5 in 41 PAH patients who had no mutations in BMPR2, ALK1, endoglin, SMAD1/4/8, BMPR1B, or Caveolin-1. Two novel missense mutations (c.2519 G>A p.G840E, c.2698 A>C p.T900P) in NOTCH3 were identified in two PAH patients. We performed functional analysis using stable cell lines expressing either wild-type or mutant NOTCH3. The protein-folding chaperone GRP78/BiP was colocalized with wild-type NOTCH3 in the endoplasmic reticulum, whereas the majority of GRP78/BiP was translocated into the nuclei of cells expressing mutant NOTCH3. Cell proliferation and viability were higher for cells expressing mutant NOTCH3 than for those expressing wild-type NOTCH3. We identified novel NOTCH3 mutations in PAH patients and revealed that these mutations were involved in cell proliferation and viability. NOTCH3 mutants induced an impairment in NOTCH3-HES5 signaling. The results may contribute to the elucidation of PAH pathogenesis.

Soluble ST2 and N-terminal pro-brain natriuretic peptide combination. Useful biomarker for predicting outcome of childhoodpulmonary arterial hypertension.

BACKGROUND: Some potential biomarkers have been reported recently in patients with pulmonary arterial hypertension (PAH), but the most clinically useful among these potential biomarkers, especially in childhood PAH, has not been identified. Therefore, this study investigated which biomarker is useful in assessing severity of and patient prognosis in childhood idiopathic PAH (IPAH)/heritable PAH (HPAH). METHODS AND RESULTS: Fifty-nine patients who were younger than 16 years at onset of IPAH/HPAH were selected. The following 10 biomarker candidates were quantified: high-sensitivity troponin T, human heart fatty acid-binding protein, N-terminal pro-brain natriuretic peptide (NT-proBNP), pentraxin-3, soluble ST2 (sST2), angiopoietin-2 (Ang-2), matrix metalloproteinase 2, tenascin C, endostatin (ES), and thymidine kinase. Functional characteristics and clinical outcomes were analyzed retrospectively. NT-proBNP, sST2, Ang-2, and ES correlated well with New York Heart Association class. On area under the receiver operating characteristic curve analysis, sST2 had a significantly good relationship with prognosis. On Kaplan-Meier curve and univariate Cox regression analyses, elevated sST2 and NT-proBNP level predicted poor outcome of the present patients with childhood IPAH/HPAH. Furthermore, patients with elevated sST2 had significantly worse prognosis among those with high NT-proBNP. CONCLUSIONS: The sST2 and NT-proBNP combination is a useful biomarker to predict clinical condition and outcome in patients with childhood IPAH/HPAH.

Tissue Doppler imaging predicts adverse outcome in children with idiopathic pulmonary arterial hypertension.

OBJECTIVE: To evaluate the clinical utility of tissue Doppler imaging (TDI) in assessment of disease severity and prognostic value in children with idiopathic pulmonary arterial hypertension (PAH). STUDY DESIGN: A prospective study was performed to evaluate TDI velocities (systolic myocardial velocity, early diastolic myocardial relaxation velocity [Em], late diastolic myocardial velocity associated with atrial contraction), brain natriuretic peptide, New York Heart Association (NYHA) functional class, and hemodynamics in 51 children (mean age; 11.6 years) with idiopathic PAH. Fifty-one healthy children with comparable demographics served as controls. RESULTS: Em, Em/late diastolic myocardial velocity associated with atrial contraction ratio, and systolic myocardial velocity at mitral annulus, septum, and tricuspid annulus in PAH were significantly reduced compared with controls. Tricuspid Em had significant inverse correlations with plasma brain natriuretic peptide levels (r = -0.60, P < .001), right ventricular end-diastolic pressure (r = -0.79, P < .001), and mean pulmonary arterial pressure (r = -0.67, P < .001). Statistically significant differences were observed in tricuspid Em between NYHA functional class II vs combined III and IV (mean and SD; 11.9 ± 4.2 cm/s vs 8.2 ± 3.6 cm/s, respectively, P = .002). Cumulative event-free survival rate was significantly lower when tricuspid Em was ≤8 cm/s (log-rank test, P < .001) CONCLUSIONS: Tricuspid Em velocity correlated with NYHA functional class as disease severity and may serve as a useful prognostic marker in children with idiopathic PAH. The present study is the initial report to evaluate TDI velocities against midterm outcome variables in a relatively large pediatric PAH population.

Transcatheter atrial septal defect closure in a patient with paradoxical brain emboli: who should treat it and who should be treated?

This report presents the case of a 51-year-old female who was admitted to a local hospital because of a persistent headache. A diagnosis of multiple cerebral infarctions was thereafter made, but there was no evidence of either atherosclerosis or atrial fibrillation. The case was thought to be a cryptogenic stroke, however, Doppler ultrasonography of the lower extremities showed venous insufficiency. Transesophageal echocardiography revealed a secundum atrial septal defect (ASD) with a left to right shunt. Therefore, the final diagnosis was paradoxical brain emboli, and transcatheter ASD closure was successfully performed by cardiologists without any sequelae.

Outcomes of childhood pulmonary arterial hypertension in BMPR2 and ALK1 mutation carriers.

Mutations in the bone morphogenetic protein receptor type 2 (BMPR2) gene and the activin receptor-like kinase 1 (ALK1) gene have been reported in heritable pulmonary arterial hypertension (HPAH) and idiopathic pulmonary arterial hypertension (IPAH). However, the relation between clinical characteristics and each gene mutation in IPAH and HPAH is still unclear, especially in childhood. The aim of this study was to determine, in a retrospective study, the influence and clinical outcomes of gene mutations in childhood IPAH and HPAH. Fifty-four patients with IPAH or HPAH whose onset of disease was at <16 years of age were included. Functional characteristics, hemodynamic parameters, and clinical outcomes were compared in BMPR2 and ALK1 mutation carriers and noncarriers. Overall 5-year survival for all patients was 76%. Eighteen BMPR2 mutation carriers and 7 ALK1 mutation carriers were detected in the 54 patients with childhood IPAH or HPAH. Five-year survival was lower in BMPR2 mutation carriers than mutation noncarriers (55% vs 90%, hazard ratio 12.54, p = 0.0003). ALK1 mutation carriers also had a tendency to have worse outcome than mutation noncarriers (5-year survival rate 64%, hazard ratio 5.14, p = 0.1205). In conclusion, patients with childhood IPAH or HPAH with BMPR2 mutation have the poorest clinical outcomes. ALK1 mutation carriers tended to have worse outcomes than mutation noncarriers. It is important to consider aggressive treatment for BMPR2 or ALK1 mutation carriers.

Missense mutations of the BMPR1B (ALK6) gene in childhood idiopathic pulmonary arterial hypertension.

BACKGROUND: Mutations in the bone morphogenetic protein receptor type 2 (BMPR2) gene, the activin receptor-like kinase 1 (ALK1) gene, and SMAD8 gene have been reported in heritable pulmonary arterial hypertension (HPAH) and in idiopathic pulmonary arterial hypertension (IPAH). However, almost 30% of HPAH cases and 60-90% of IPAH cases have no mutations in those genes. This suggests that there remain unidentified genes associated with HPAH and IPAH. METHODS AND RESULTS: This study screened for mutations in endoglin, SMAD1, SMAD2, SMAD3, SMAD4, SMAD5, SMAD6, SMAD7, bone morphogenetic protein receptor type 1A (BMPR1A) and bone morphogenetic protein receptor type 1B (BMPR1B) genes in 43 IPAH patients who had no mutations in BMPR2, ALK1 and SMAD8. Two missense mutations (c.479 G>A S160N, c.1176 C>A F392L) in BMPR1B were each identified in 2 IPAH patients. Immunoblot analysis revealed that the BMPR1B F392L protein promoted SMAD8 phosphorylation. The response to BMP was analyzed using promoter-reporter activities. The transcriptional activation of the BMPR1B F392L protein with SMAD8 increased above that of wild-type BMPR1B with SMAD8, and those of BMPR1B S160N and F392L with SMAD8 and SMAD4 were each increased above those of the wild-type BMPR1B with SMAD8 and SMAD4. CONCLUSIONS: We identified 2 novel mutations in BMPR1B in 2 patients with IPAH. Our study suggests that BMPR1B mutations are associated with the pathogenesis of IPAH.