🏷

Classifications

Harrison's Part

◆

Subtypes

3

Classical IPAH (no cardiopulmonary comorbidities, preserved DLCO)

The canonical IPAH phenotype: younger, predominantly female patients without cardiopulmonary comorbidities and with a diffusing capacity for carbon monoxide (DLCO) of 45% predicted or more. This subgroup shows the largest treatment response to PAH pathway therapy.

Show evidence (1 reference)

PMID:35777416 SUPPORT Human Clinical

"patients with classical IPAH (defined by the absence of cardiopulmonary comorbidities and a DLCO of 45% or more predicted)"

The COMPERA/ASPIRE registry analysis defines classical IPAH explicitly by absence of cardiopulmonary comorbidities and preserved DLCO.

IPAH with a lung phenotype (low DLCO, smoking history)

An emerging IPAH subgroup that meets diagnostic criteria for IPAH but has a severely reduced DLCO (<45% predicted) and a smoking history, with normal or near-normal spirometry and little or no parenchymal lung disease on CT. These patients are older, far less female-predominant, and respond poorly to PAH therapy, resembling Group 3 pulmonary hypertension more than classical IPAH.

Show evidence (2 references)

PMID:35777416 SUPPORT Human Clinical

"Among patients meeting diagnostic criteria for idiopathic pulmonary arterial hypertension (IPAH), there is an emerging lung phenotype characterised by a low diffusion capacity for carbon monoxide (DLCO) and a smoking history."

This directly establishes the low-DLCO smoking-associated lung phenotype as a distinct subgroup within diagnostically defined IPAH.

PMID:35777416 SUPPORT Human Clinical

"Most patients with IPAH and a lung phenotype had normal or near normal spirometry, a severe reduction in DLCO, with the majority having no or a mild degree of parenchymal lung involvement on chest computed tomography."

Characterises the physiological and radiological signature that separates this subgroup from Group 3 pulmonary hypertension due to overt lung disease.

Acutely vasoreactive, long-term calcium-channel-blocker-responsive IPAH

A small IPAH subgroup identified by acute pulmonary vasodilator testing at diagnostic right-heart catheterisation. Roughly one in eight IPAH patients is an acute responder, but fewer than 10% sustain long-term benefit on calcium-channel blocker monotherapy. Long-term responders have an excellent prognosis, making vasoreactivity testing a distinctive and clinically decisive step in IPAH (and heritable/drug-associated PAH) that is not applied across other PH groups.

Show evidence (2 references)

PMID:15939821 SUPPORT Human Clinical

"Among the 70 patients who displayed acute pulmonary vasoreactivity (12.6%; 95% CI, 9.8% to 15.3%) and received CCB therapy, only 38 showed long-term improvement (6.8%; 95% CI, 4.7% to 8.9%)."

Quantifies both the acute-vasoreactive and the durable calcium-channel-blocker-responsive fractions of an IPAH referral cohort.

PMID:15939821 SUPPORT Human Clinical

"Long-term CCB responders represent <10% of IPAH patients evaluated in a pulmonary vascular referral center."

Establishes the small size of the durable vasoresponder subgroup within IPAH.

◈

Mechanistic Hypotheses

1

Endothelial ferroptosis as an upstream inflammatory driver of IPAH remodeling

ipah_ferroptosis_inflammation EMERGING

Evidence balance 2 support

An emerging model in which lipid peroxidation and ferroptotic death of pulmonary arterial endothelial cells release damage-associated molecular patterns that activate complement, recruit inflammatory macrophages and drive smooth muscle proliferation. Multi-omic and genetic-association data in humans plus rescue by the ferroptosis inhibitor ferrostatin-1 in monocrotaline rats support the model, but the evidence is preclinical for therapy and derives from PAH broadly rather than IPAH specifically.

Show evidence (2 references)

PMID:39421926 SUPPORT Model Organism

"Ferrostatin-1, a small-molecule ferroptosis inhibitor, mitigated PAH severity in monocrotaline rats."

Provides the in vivo pharmacological rescue that anchors the ferroptosis hypothesis.

PMID:39421926 SUPPORT Other

"Ferroptosis promotes PAH through metabolic and inflammatory mechanisms in the pulmonary vasculature."

States the hypothesis in the authors' own terms. Evidence source is OTHER because the conclusion integrates human multi-omic, rodent and in vitro data.

?

Discussions and Knowledge Gaps

2

After comprehensive gene-panel and genome sequencing has excluded known pathogenic variants, and all associated conditions and exposures have been ruled out, what actually initiates pulmonary vascular disease in the remaining genuinely idiopathic majority of IPAH patients?

KNOWLEDGE GAP OPEN gap_ipah_residual_etiology_after_genetic_testing

Attached to

pathophysiology#Unidentified Initiating Insult in a Susceptible Pulmonary Vasculature pathophysiology#Occult Rare Variant Burden and Reclassification to Heritable PAH genetic#BMPR2

This entry models IPAH as a diagnosis of exclusion with an explicit trigger node that names no trigger. Pooled genetic testing accounts for roughly one in five IPAH diagnoses by reclassifying them as heritable disease, which sharpens rather than resolves the question: the remaining four in five have no identified cause at all. Resolving what initiates disease in that residual population is the single largest mechanistic gap in this entry and determines whether IPAH remains a coherent disease entity or fragments into further aetiological subtypes, as the low-DLCO lung phenotype already suggests.

Show evidence (2 references)

PMID:40229839 SUPPORT Human Clinical

"the frequency of P/LP variants in our cohort (10.48%) is lower than the overall average of 17.75% from the meta-analysis"

Quantifies the fraction of IPAH explained by BMPR2 genetics, and by implication the much larger fraction that remains unexplained.

PMID:39209481 SUPPORT Human Clinical

"these cohorts are largely of European origin; greater diversity will be essential to characterise the full extent of genomic variation contributing to PH risk and treatment responses."

Identifies ancestry bias in existing PAH genomic cohorts as a specific reason the residual unexplained fraction may be overestimated in non-European populations.

Why is IPAH roughly four times more common in women than in men, and why is this female predominance concentrated in the classical phenotype and largely absent in the low-DLCO lung phenotype?

KNOWLEDGE GAP OPEN gap_ipah_female_predominance_mechanism

Attached to

prevalence#Idiopathic PAH patients across epidemiological studies has_subtypes#Classical IPAH has_subtypes#Lung phenotype IPAH pathophysiology#Unidentified Initiating Insult in a Susceptible Pulmonary Vasculature

The entry records a 4.1:1 female-to-male incidence ratio in IPAH and shows that it collapses in the lung phenotype, but offers no mechanism. Sex-hormone metabolism, sex-differential BMP-pathway regulation and sex differences in right ventricular adaptation are all candidate explanations, and they make divergent predictions. Because the sex distribution differs so sharply between the two registry-defined phenotypes, resolving this would help decide whether classical IPAH and the lung phenotype are one disease with modifiers or two diseases sharing a haemodynamic definition.

Show evidence (2 references)

PMID:37461108 SUPPORT Human Clinical

"women have a higher incidence rate than men across multiple studies (4.3:1 in the total PAH group and 4.1:1 in the IPAH category)"

Establishes the magnitude of the female predominance the gap seeks to explain.

PMID:35777416 SUPPORT Human Clinical

"While 99 (77%) patients in COMPERA and 133 (72%) patients in ASPIRE with classical IPAH were female, there was a lower proportion of female patients in the IPAH and a lung phenotype cohort"

Documents the phenotype-dependent collapse of the female predominance that motivates the question.

⚙

Pathophysiology

8

Unidentified Initiating Insult in a Susceptible Pulmonary Vasculature

The defining feature of IPAH is that no associated condition, drug or toxin exposure, or family history explains the disease after a complete evaluation. This is an epistemic rather than a biological null: IPAH is best modelled as a threshold disorder in which incompletely characterised genetic susceptibility, epigenetic dysregulation, sex-hormone biology and acquired vascular stresses combine to cross a disease threshold, with no single trigger identifiable in the individual patient. This node substitutes for the disorder-specific trigger that heritable PAH (a germline BMPR2-pathway lesion) and drug- or toxin-induced PAH (a culprit exposure) each supply, and it is the reason IPAH is a diagnosis of exclusion.

pulmonary artery UBERON:0002012

Downstream

Pulmonary Arterial Endothelial Dysfunction Whatever the unresolved initiating insult, the earliest identifiable lesion in IPAH is dysfunction of the pulmonary arterial endothelium.

Show evidence (2 references)

DOI:10.3390/biomedicines13071773 SUPPORT Human Clinical

"The majority of PAH cases are idiopathic; other common etiologies include connective tissue disease-associated PAH, congenital heart disease, and portopulmonary hypertension."

Confirms that idiopathic disease - PAH without an identified associated cause - is the largest aetiological category within Group 1 PAH.

PMID:36302552 SUPPORT Human Clinical

"Pulmonary arterial hypertension (PAH) is a rare disease that can be caused by (likely) pathogenic germline genomic variants."

Supports that an aetiological cause may be latent rather than absent in patients initially designated idiopathic; PARTIAL because the statement is PAH-wide.

Occult Rare Variant Burden and Reclassification to Heritable PAH

A substantial minority of patients who satisfy IPAH criteria are subsequently found on comprehensive PAH gene-panel or genome sequencing to carry a rare pathogenic or likely pathogenic germline variant - most often a loss-of-function BMPR2 allele, and less often variants in TBX4, ATP13A3, SOX17, GDF2, AQP1 or other curated PAH genes. Because incomplete, age- and sex-dependent penetrance means many carriers have no affected relative, absence of family history does not exclude a germline cause. Detecting such a variant reclassifies the patient as heritable PAH and opens cascade screening of relatives. This node is the explicit mechanistic boundary between this entry and Heritable Pulmonary Arterial Hypertension: it is not a separate remodeling mechanism but a statement that a fraction of the IPAH population is misclassified heritable disease.

Downstream

Pulmonary Arterial Endothelial Dysfunction In the variant-positive fraction, reduced BMP receptor signalling is the identifiable molecular cause of the endothelial lesion, as in heritable PAH.

Show evidence (3 references)

PMID:40229839 SUPPORT Human Clinical

"A meta-analysis, performed with MOOSE, included 24 studies involving 3124 IPAH patients and 470 P/LP variants."

Establishes the scale of the pooled IPAH genetic-testing evidence underpinning this node.

PMID:40229839 SUPPORT Human Clinical

"Analysis of 105 adult IPAH patients in Russia revealed 11 patients (10.48%) as carriers of pathogenic or likely pathogenetic (P/LP) BMPR2 variants."

Directly documents occult pathogenic BMPR2 carriage within a clinically diagnosed IPAH cohort.

PMID:36302552 SUPPORT Human Clinical

"Benefits of including molecular genetic testing within the management protocol of patients with PAH include the identification of individuals misclassified by other diagnostic approaches"

The international consensus explicitly frames genetic testing as a means of correcting misclassification, the mechanism modelled by this node.

Pulmonary Arterial Endothelial Dysfunction

Pulmonary arterial endothelial cells lose homeostatic function: BMP receptor signalling is reduced (by germline lesion in the occult-variant fraction, and by acquired suppression otherwise), nitric-oxide and prostacyclin production fall while endothelin-1 rises, barrier integrity is lost, and an apoptosis-prone population is replaced by apoptosis-resistant, hyperproliferative cells. This is the conserved entry point into the shared pulmonary vascular remodeling module; IPAH substitutes an unidentified or occult-genetic insult for the germline BMPR2 lesion of heritable PAH.

pulmonary artery endothelial cell CL:1001568

BMP signaling pathway GO:0030509 ↓ DECREASED nitric oxide biosynthetic process GO:0006809 ↓ DECREASED endothelin receptor signaling pathway GO:0086100 ↑ INCREASED

pulmonary artery UBERON:0002012

Downstream

Pulmonary Artery Smooth Muscle Cell Proliferation and Vasoconstriction Loss of endothelium-derived vasodilator and antiproliferative signalling releases the medial smooth muscle compartment.

T and NK Cell CCL5-Mediated Immune-Vascular Crosstalk Injured endothelium participates in chemokine-mediated recruitment of lymphoid cells to the pulmonary vascular wall.

Show evidence (2 references)

PMID:36603064 SUPPORT Other

"Compelling evidence from animal models suggests endothelial cell dysfunction is a key initial trigger of pulmonary vascular remodeling, which is characterised by hyperproliferation and early apoptosis followed by enrichment of apoptosis-resistant populations."

Establishes endothelial dysfunction as the conserved initiating cellular lesion of pulmonary vascular remodeling. Evidence source is OTHER because this is a review synthesising animal-model and human data.

DOI:10.3390/biomedicines13071773 SUPPORT Human Clinical

"The pathophysiology of PAH involves the following four primary pathways: nitric oxide, endothelin-1, prostacyclin, and activin/bone morphogenetic protein (BMP)."

Names the four endothelium-centred signalling axes whose imbalance defines this node and which the approved therapies target.

T and NK Cell CCL5-Mediated Immune-Vascular Crosstalk

Integrated analysis of IPAH lung transcriptomes, histopathology scoring and single-cell RNA sequencing identifies CXCL9, CCL5, GZMA and GZMK as inflammation-associated hub genes distinguishing IPAH lungs from controls, with CCL5 and GZMA expressed predominantly by T and NK cells. CCL5 mediates interaction of these lymphoid populations with pulmonary endothelial cells, smooth muscle cells and fibroblasts through multiple receptors, defining an adaptive immune-vascular amplification arm of IPAH remodeling. This is an IPAH-specific refinement of the generic perivascular-inflammation theme; it is discovery-stage and not a validated clinical target.

T cell CL:0000084 natural killer cell CL:0000623

inflammatory response GO:0006954 ↑ INCREASED

pulmonary artery UBERON:0002012

Downstream

Pulmonary Artery Smooth Muscle Cell Proliferation and Vasoconstriction Chemokine-mediated immune-vascular crosstalk amplifies the proliferative response of the medial smooth muscle compartment.

Show evidence (2 references)

PMID:38797830 SUPPORT Human Clinical

"Through an extensive bioinformatics analysis, CXCL9, CCL5, GZMA and GZMK were identified as hub genes that distinguished IPAH patients from controls."

Identifies the IPAH-specific inflammatory hub genes underpinning this node from human IPAH lung transcriptomes.

PMID:38797830 SUPPORT Human Clinical

"only CCL5 and GZMA were highly expressed in T and NK cells, where CCL5 mediated T and NK cell interaction with endothelial cells, smooth muscle cells, and fibroblasts through multiple receptors."

Directly supports the CCL5-mediated lymphoid-to-vascular-cell interaction that defines this amplifier node.

Pulmonary Artery Smooth Muscle Cell Proliferation and Vasoconstriction

Paracrine signals from the dysfunctional endothelium, compounded by inflammatory input, drive a proliferative, migratory and apoptosis-resistant phenotype in pulmonary artery smooth muscle cells, together with sustained vasoconstriction. In the small acutely vasoreactive IPAH subgroup, the vasoconstrictive component still dominates over fixed remodeling, which is why those patients respond durably to calcium-channel blockade.

pulmonary artery smooth muscle cell CL:0002591

smooth muscle cell proliferation GO:0048659 ↑ INCREASED resistance to apoptosis GO:0043066 ↑ INCREASED vasoconstriction GO:0042310 ↑ INCREASED

pulmonary artery UBERON:0002012

Downstream

Obstructive Pulmonary Vascular Remodeling Medial expansion and muscularisation of peripheral arterioles narrow the pulmonary vascular lumen.

Show evidence (2 references)

PMID:37461108 SUPPORT Human Clinical

"Multiple biological processes, such as smooth muscle proliferation, endothelial dysfunction, inflammation, and resistance to apoptosis, are associated with PAH."

Names smooth muscle proliferation and apoptosis resistance as core processes of the PAH remodeling cascade this node represents.

PMID:39421926 SUPPORT In Vitro

"Ferroptotic pulmonary arterial endothelial cell damage-associated molecular patterns restructured the transcriptomic signature and mitochondrial morphology, promoted the proliferation of pulmonary artery smooth muscle cells, and created a proinflammatory phenotype in monocytes in vitro."

Provides a specific in vitro demonstration that injured endothelium drives smooth muscle proliferation; PARTIAL because the mechanism (ferroptotic DAMPs) is one of several routes and is not IPAH-specific.

Obstructive Pulmonary Vascular Remodeling

Sustained smooth muscle proliferation, adventitial fibroblast activation, matrix deposition and neointima formation remodel the wall of small pulmonary arteries, producing medial hypertrophy, eccentric and concentric intimal fibrosis, in-situ thrombosis and plexiform lesions that obliterate the lumen. This structural obstruction is the central effector shared with heritable, associated and drug- or toxin-induced PAH, and it is largely irreversible once established.

pulmonary artery smooth muscle cell CL:0002591 fibroblast CL:0000057

blood vessel remodeling GO:0001974 ↕ DYSREGULATED extracellular matrix organization GO:0030198 ⚠ ABNORMAL

pulmonary artery UBERON:0002012

Downstream

Increased Pulmonary Vascular Resistance Fixed luminal obstruction, added to dynamic vasoconstriction, raises resistance across the pulmonary bed.

Show evidence (2 references)

PMID:38797830 SUPPORT Human Clinical

"is central to the irreversible progression of IPAH"

IPAH-specific statement that pulmonary vascular remodeling, marked by arteriolar eccentricity and occlusive intimal thickening, is the central and largely irreversible driver of disease progression.

PMID:29650961 SUPPORT Human Clinical

"Idiopathic and heritable pulmonary arterial hypertension (PAH) are rare disorders characterised by occlusion of arterioles in the lung"

Explicitly groups idiopathic with heritable PAH around the shared lesion of arteriolar occlusion, the basis for conformance to the shared module.

Increased Pulmonary Vascular Resistance

The combination of fixed structural obstruction and sustained vasoconstriction raises pulmonary vascular resistance and reduces pulmonary arterial compliance, while pulmonary arterial wedge pressure remains normal - the pre-capillary haemodynamic signature confirmed at right-heart catheterisation that defines PAH and separates it from Group 2 pulmonary hypertension due to left heart disease.

vasoconstriction GO:0042310 ↑ INCREASED

Downstream

Precapillary Pulmonary Arterial Hypertension with Right Ventricular Failure Elevated resistance imposes a chronic pressure load on the right ventricle.

Show evidence (1 reference)

DOI:10.3390/biomedicines13071773 SUPPORT Human Clinical

"Pulmonary arterial hypertension (PAH) is a specific subset of PH characterized by a normal pulmonary arterial wedge pressure (PAWP), combined with elevated mPAP and increased pulmonary vascular resistance (PVR), without other causes of pre-capillary hypertension such as lung diseases or chronic..."

Defines the pre-capillary haemodynamic state of this node and its explicit exclusion of Group 3 and Group 4 pulmonary hypertension.

Precapillary Pulmonary Arterial Hypertension with Right Ventricular Failure

Sustained elevation of pulmonary arterial pressure imposes chronic pressure overload on the right ventricle. Hypertrophy compensates initially, but ischaemia, fibrosis, dilation and tricuspid regurgitation eventually reduce right ventricular output, producing systemic venous congestion, exertional syncope and death from right heart failure.

right ventricular hypertrophy GO:0003300 ↑ INCREASED

heart right ventricle UBERON:0002080

Downstream

Exertional dyspnea Reduced cardiac output reserve produces exertional breathlessness.

Exertional syncope Inability to raise cardiac output during exertion causes syncope.

Right ventricular failure Maladaptive right ventricular remodeling culminates in overt failure.

Peripheral edema Right-heart congestion raises systemic venous pressure.

Show evidence (2 references)

DOI:10.3390/biomedicines13071773 SUPPORT Human Clinical

"Dysregulation of these pathways leads to a progressive vasculopathy marked by vasoconstriction, vascular proliferation, elevated right heart afterload, and ultimately right-sided heart failure."

Directly supports the terminal right-ventricular consequence of the remodeling cascade.

PMID:38797830 SUPPORT Human Clinical

"Idiopathic pulmonary arterial hypertension (IPAH) is a devastating pulmonary vascular disease characterized by a progressive increase in pulmonary vascular resistance and right heart failure"

IPAH-specific confirmation that rising pulmonary vascular resistance culminates in right heart failure.

✶

Histopathology

1

Remodeled pulmonary arterioles with immune cell accumulation

IPAH lung pathology shows eccentric and concentric intimal fibrosis with occlusive thickening of small pulmonary arterioles, medial hypertrophy, in-situ thrombosis and plexiform lesions, together with accumulation of immune cells around and within the remodeled arterioles. Lung biopsy is not required for and is generally avoided in routine diagnosis.

Show evidence (1 reference)

PMID:38797830 SUPPORT Human Clinical

"Accumulation of immune cells in remodeled pulmonary arterioles is a common finding in IPAH lung tissue"

IPAH-specific histopathological description of remodeled arterioles with immune cell infiltration.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

●

Phenotypes

10

Cardiovascular 2

Pulmonary arterial hypertension HP:0002092

Show evidence (1 reference)

DOI:10.3390/biomedicines13071773 SUPPORT Human Clinical

"Pulmonary arterial hypertension (PAH) is a specific subset of PH characterized by a normal pulmonary arterial wedge pressure (PAWP), combined with elevated mPAP and increased pulmonary vascular resistance (PVR)"

Establishes the defining haemodynamic phenotype.

Exertional syncope HP:0001279

Show evidence (1 reference)

PMID:29540357 SUPPORT Human Clinical

"Patients with PAH have dyspnea, reduced exercise capacity, exertional syncope, and premature death from right ventricular failure."

Explicitly identifies exertional syncope as a characteristic PAH symptom.

Metabolism 1

Peripheral edema HP:0012398

Show evidence (1 reference)

PMID:40229839 SUPPORT Human Clinical

"Peripheral oedema, n (%) 52 (49.5) mPAP , mmHg 55.04 ± 15.928"

Reports peripheral oedema in 52 of 105 participants (49.5%) in a contemporary IPAH/HPAH cohort; the adjacent mPAP row preserves the source table context.

Constitutional 2

Fatigue HP:0012378

Show evidence (1 reference)

DOI:10.1183/13993003.01325-2024 SUPPORT Human Clinical

"Pulmonary arterial hypertension leads to significant impairment in haemodynamics, right heart function, exercise capacity, quality of life and survival."

Supports impaired exercise capacity and quality of life; fatigue is the symptom-level expression, hence PARTIAL.

Exercise intolerance HP:0003546

Show evidence (1 reference)

PMID:29540357 SUPPORT Human Clinical

"Patients with PAH have dyspnea, reduced exercise capacity, exertional syncope, and premature death from right ventricular failure."

Directly supports reduced exercise capacity as a cardinal PAH manifestation.

Other 5

Increased pulmonary vascular resistance HP:0005317

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:38797830 SUPPORT Human Clinical

"Idiopathic pulmonary arterial hypertension (IPAH) is a devastating pulmonary vascular disease characterized by a progressive increase in pulmonary vascular resistance and right heart failure"

IPAH-specific description of progressively increasing pulmonary vascular resistance.

Exertional dyspnea HP:0002875

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:29540357 SUPPORT Human Clinical

"Patients with PAH have dyspnea, reduced exercise capacity, exertional syncope, and premature death from right ventricular failure."

Lists dyspnoea among the cardinal manifestations of PAH.

Right ventricular hypertrophy HP:0001667

Show evidence (1 reference)

PMID:38716930 SUPPORT Human Clinical

"Pulmonary arterial hypertension (PAH) is a rare and life-threatening vascular disorder, characterised by abnormal remodelling of the pulmonary vessels and elevated pulmonary artery pressure, leading to right ventricular hypertrophy and right-sided heart failure."

Supports right ventricular hypertrophy as a core downstream phenotype of PAH.

Right ventricular failure HP:0001708

Show evidence (1 reference)

PMID:37376028 SUPPORT Human Clinical

"Pulmonary arterial hypertension (PAH) is a malignant pulmonary vascular syndrome characterized by a progressive increase in pulmonary vascular resistance and pulmonary arterial pressure, which eventually leads to right heart failure and even death."

Directly supports right heart failure as the terminal clinical consequence.

Decreased DLCO HP:0045051

Show evidence (1 reference)

PMID:35777416 SUPPORT Human Clinical

"patients diagnosed with IPAH and a lung phenotype defined by a DLCO of less than 45% predicted and a smoking history"

Directly defines the low-DLCO criterion for this IPAH subgroup.

🧬

Genetic Associations

5

BMPR2 (Rare pathogenic or likely pathogenic germline BMPR2 variants are found in a substantial minority of patients diagnosed with IPAH; their identification reclassifies the patient as heritable PAH.)

Gene: BMPR2 hgnc:1078 relationship_type: SUSCEPTIBILITY variant_origin: GERMLINE

Show evidence (1 reference)

PMID:40229839 SUPPORT Human Clinical

"Idiopathic pulmonary arterial hypertension (IPAH) is a rare and severe form of pulmonary hypertension, with a genetic basis most commonly associated with mutations in the BMPR2 gene."

Establishes BMPR2 as the predominant genetic contributor within clinically diagnosed IPAH.

TBX4 (Rare TBX4 variants are found among non-BMPR2 gene-panel-positive patients presenting with apparently idiopathic PAH.)

Gene: TBX4 hgnc:11603 relationship_type: SUSCEPTIBILITY variant_origin: GERMLINE

Show evidence (1 reference)

PMID:40229839 SUPPORT Human Clinical

"four P/LP variants in TBX4, ATP13A3 and AQP1 genes from 27 IPAH genes in 3 patients"

Documents pathogenic TBX4 variants recovered from a clinically diagnosed IPAH cohort.

ATP13A3 (ATP13A3 is one of the non-BMPR2 genes recurrently implicated in idiopathic and heritable PAH cohorts.)

Gene: ATP13A3 hgnc:24113 relationship_type: SUSCEPTIBILITY variant_origin: GERMLINE

Show evidence (1 reference)

PMID:29650961 SUPPORT Human Clinical

"rare variants in ATP13A3, AQP1 and SOX17, and provide independent validation of"

Whole-genome sequencing of an idiopathic and heritable PAH cohort identified ATP13A3 among the newly implicated genes.

SOX17 (SOX17 is a developmental-vascular PAH gene discovered through case-control rare variant burden analysis of idiopathic and heritable PAH cohorts.)

Gene: SOX17 hgnc:18122 relationship_type: SUSCEPTIBILITY variant_origin: GERMLINE

Show evidence (1 reference)

PMID:29650961 SUPPORT Human Clinical

"rare variants in ATP13A3, AQP1 and SOX17, and provide independent validation of"

Whole-genome sequencing of an idiopathic and heritable PAH cohort identified SOX17 among the newly implicated genes.

GDF2 (GDF2 (BMP9) was independently validated as a PAH gene through rare missense variant burden in idiopathic and heritable PAH.)

Gene: GDF2 hgnc:4217 relationship_type: SUSCEPTIBILITY variant_origin: GERMLINE

Show evidence (1 reference)

PMID:29650961 SUPPORT Human Clinical

"This revealed significant overrepresentation of rare variants in GDF2 after correction for multiple testing"

Supports GDF2 as a validated rare-variant PAH gene recoverable from apparently idiopathic cases.

💊

Medical Actions

6

Endothelin receptor antagonist therapy

Action: Pharmacotherapy NCIT:C15986

Agent: endothelin receptor antagonist NCIT:C28313 macitentan CHEBI:76607 ambrisentan CHEBI:135949 bosentan CHEBI:51450

Ambrisentan, bosentan or macitentan block endothelin-1 signalling on the pulmonary vascular wall. An endothelin receptor antagonist combined with a PDE5 inhibitor is the usual initial oral dual therapy for low- and intermediate-risk IPAH without major cardiopulmonary comorbidity.

Mechanism Target:

INHIBITS Pulmonary Arterial Endothelial Dysfunction — Blocks the endothelin-1 arm of the endothelial vasoactive imbalance that initiates the remodeling cascade.

Show evidence (1 reference)

DOI:10.1183/13993003.01325-2024 SUPPORT Human Clinical

"Current therapies have mechanisms of action involving signallingviaone of four pathways: endothelin-1, nitric oxide, prostacyclin and bone morphogenetic protein/activin signalling."

Establishes endothelin-1 as one of the four validated therapeutic pathways in PAH.

Nitric oxide-cGMP pathway therapy

Action: Pharmacotherapy NCIT:C15986

Agent: sildenafil CHEBI:9139 tadalafil CHEBI:71940 riociguat CHEBI:76018

Phosphodiesterase-5 inhibitors (sildenafil, tadalafil) potentiate cGMP signalling downstream of nitric oxide; riociguat instead stimulates soluble guanylate cyclase directly. Riociguat must not be combined with a PDE5 inhibitor because of the risk of hypotension.

Mechanism Target:

INHIBITS Pulmonary Artery Smooth Muscle Cell Proliferation and Vasoconstriction — Augmenting cGMP signalling opposes smooth muscle vasoconstriction and proliferation.

Show evidence (1 reference)

DOI:10.1183/13993003.01325-2024 SUPPORT Human Clinical

"Current therapies have mechanisms of action involving signallingviaone of four pathways: endothelin-1, nitric oxide, prostacyclin and bone morphogenetic protein/activin signalling."

Establishes the nitric oxide pathway as a validated therapeutic axis in PAH.

Prostacyclin pathway therapy

Action: Pharmacotherapy NCIT:C15986

Agent: epoprostenol NCIT:C61748 treprostinil CHEBI:50861 selexipag CHEBI:90844

Epoprostenol, treprostinil, iloprost and the oral prostacyclin receptor agonist selexipag restore prostacyclin signalling. Parenteral prostacyclin, especially intravenous epoprostenol, is added for high-risk disease, and efficacy is greater with parenteral than with non-parenteral therapy.

Mechanism Target:

RESTORES Pulmonary Arterial Endothelial Dysfunction — Replaces the prostacyclin signalling lost through pulmonary endothelial dysfunction.

Show evidence (1 reference)

DOI:10.1183/13993003.01325-2024 SUPPORT Human Clinical

"Efficacy has generally been greater with therapeutic combinations and with parenteral therapy compared with monotherapy or nonparenteral therapies, and maximal medical therapy is now four-drug therapy."

Supports escalation to parenteral prostacyclin within combination therapy for higher-risk PAH.

Sotatercept

Action: targeted therapy Ontology label: Targeted Therapy NCIT:C93352

Agent: sotatercept NCIT:C80038

An ActRIIA-Fc ligand trap that sequesters activin-family ligands and rebalances activin/BMP signalling. It is the first approved PAH therapy directed at the TGF-beta-superfamily imbalance underlying vascular remodeling rather than at vascular tone alone, and is added when low-risk status is not achieved on background therapy.

Mechanism Target:

INHIBITS Obstructive Pulmonary Vascular Remodeling — Rebalancing activin versus BMP signalling targets the proliferative remodeling process itself rather than vascular tone.

RESTORES Pulmonary Arterial Endothelial Dysfunction — Restores the balance of the BMP/activin arm of endothelial signalling that is depressed in PAH.

Show evidence (2 references)

PMID:38716930 SUPPORT Human Clinical

"Sotatercept, which contains the extracellular domain of another transforming growth factor-β family type II receptor ActRIIA fused to immunoglobin Fc domain, was recently approved by the FDA as a treatment for PAH."

Establishes sotatercept's molecular design and approved status in PAH.

PMID:37376028 SUPPORT Human Clinical

"Through unremitting efforts, new therapeutic drugs such as sotatercept have emerged, injecting new vitality into this field."

Positions sotatercept as the therapeutic advance beyond the three classical vasodilator pathways.

Calcium channel blocker therapy in acute vasoresponders

Action: Pharmacotherapy NCIT:C15986

Agent: calcium channel blocker NCIT:C333 nifedipine CHEBI:7565 amlodipine CHEBI:2668 diltiazem CHEBI:101278

High-dose amlodipine, nifedipine or diltiazem is reserved for the small IPAH subgroup with a positive acute vasodilator test, with close reassessment because only a minority of acute responders sustain long-term benefit. Empiric calcium channel blockade without a positive vasoreactivity test is unsafe in PAH. This is the clearest example of IPAH-specific, mechanism-stratified therapy.

Mechanism Target:

INHIBITS Pulmonary Artery Smooth Muscle Cell Proliferation and Vasoconstriction — Blocks the vasoconstrictive component of the node, which remains dominant over fixed remodeling in the acutely vasoreactive subgroup.

Show evidence (2 references)

PMID:15939821 SUPPORT Human Clinical

"Acute responders, defined by a fall in both mean pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR) >20%, received long-term oral CCB."

Documents the vasoreactivity-gated indication for long-term calcium channel blockade in IPAH.

PMID:15939821 SUPPORT Human Clinical

"After 7.0+/-4.1 years, all but 1 long-term CCB responders were alive in NYHA class I or II, with a sustained hemodynamic improvement."

Supports the excellent long-term outcome of the durable calcium-channel-blocker responder subgroup.

Lung transplantation

Action: organ transplantation Ontology label: Organ Transplantation NCIT:C15289

Bilateral lung or heart-lung transplantation is considered for selected patients with an inadequate response to maximal medical therapy.

Mechanism Target:

BYPASSES Obstructive Pulmonary Vascular Remodeling — Replacing the remodeled pulmonary vascular bed bypasses the central effector of the disease.

Show evidence (1 reference)

DOI:10.1183/13993003.01325-2024 SUPPORT Human Clinical

"Lung transplantation remains an option for selected patients with an inadequate response to therapies."

Supports transplantation for refractory advanced disease.

🌍

Environmental Factors

2

Smoking history in the IPAH lung phenotype

A smoking history, together with a severely reduced DLCO, defines the IPAH lung phenotype. Smoking is not a validated cause of classical IPAH; in this subgroup it marks a presumably smoking-related form of pulmonary vascular disease that behaves more like Group 3 pulmonary hypertension.

Show evidence (1 reference)

PMID:35777416 SUPPORT Human Clinical

"A cohort of patients meeting diagnostic criteria for IPAH with a distinct, presumably smoking-related form of pulmonary hypertension accompanied by a low DLCO, resemble patients with pulmonary hypertension due to lung disease rather than classical IPAH."

Directly links smoking history to the distinct low-DLCO IPAH subgroup while separating it from classical IPAH.

Mechanism Target:

MODULATES Unidentified Initiating Insult in a Susceptible Pulmonary Vasculature — Also modulating rather than predisposing, and for a reason the entry states itself: smoking is not a validated cause of classical disease here, and in this subgroup it marks a presumably smoking-related pulmonary vascular disease that behaves more like pulmonary hypertension due to lung disease. What the exposure modifies is which entity the patient has rather than the mechanism within it, which is the same kind of claim as the absence link above and is why both point at the same node.

Show evidence (1 reference)

PMID:35777416 SUPPORT Human Clinical

"A cohort of patients meeting diagnostic criteria for IPAH with a distinct, presumably smoking-related form of pulmonary hypertension accompanied by a low DLCO, resemble patients with pulmonary hypertension due to lung disease rather than classical IPAH."

Registry analysis identifying patients who meet the diagnostic criteria but have a presumably smoking-related form with low diffusing capacity, resembling pulmonary hypertension due to lung disease rather than the classical entity.

Absence of a recognised drug, toxin or associated-disease exposure

IPAH requires that recognised PAH-associated exposures - anorexigens, methamphetamine, dasatinib and other implicated drugs - and associated conditions such as connective tissue disease, congenital heart disease, HIV and portal hypertension be excluded. Identifying such an exposure moves the case to Drug- or Toxin-Induced PAH or to the relevant associated-PAH entity.

Show evidence (1 reference)

DOI:10.3390/biomedicines13071773 SUPPORT Human Clinical

"The majority of PAH cases are idiopathic; other common etiologies include connective tissue disease-associated PAH, congenital heart disease, and portopulmonary hypertension."

Names the associated aetiologies whose absence defines the idiopathic designation.

Mechanism Target:

MODULATES Unidentified Initiating Insult in a Susceptible Pulmonary Vasculature — The strangest link in this backfill and worth stating plainly: this records a classification criterion, not a mechanism. The exposure is an absence, so it cannot act on anything, and the node it targets is described by this entry as epistemic rather than biological, holding the fact that no cause has been found. Absence and node are therefore the same statement, which is why the link is direct, and modulating is used because no other value in the enum is honest for something that decides which entity you are looking at rather than what happens inside it. Identifying such an exposure moves the case out of this entry entirely.

Show evidence (1 reference)

DOI:10.3390/biomedicines13071773 SUPPORT Human Clinical

"The majority of PAH cases are idiopathic; other common etiologies include connective tissue disease-associated PAH, congenital heart disease, and portopulmonary hypertension."

Names the associated aetiologies whose absence defines the idiopathic designation, recording that most cases are idiopathic while connective tissue disease, congenital heart disease and portopulmonary hypertension account for others. It supplies the exclusion list rather than any effect.

🔬

Biochemical Markers

1

N-terminal pro-B-type natriuretic peptide (NT-proBNP) (INCREASED)

Context: Natriuretic peptide level reflects right ventricular wall stress and is one of the three non-invasive variables shared across validated PAH risk-stratification tools; it is also a standard trial endpoint. It is a severity and prognosis marker, not a diagnostic test for IPAH.

Show evidence (1 reference)

PMID:36877098 SUPPORT Human Clinical

"change in N-terminal pro-B-type natriuretic peptide level"

NT-proBNP was a prespecified endpoint in the phase 3 PAH trial programme, supporting its role as a disease-activity biomarker.

🔬

Diagnosis

6

Right heart catheterisation with exclusion of Groups 2-5 and associated PAH

Diagnosis requires invasive confirmation of pre-capillary pulmonary hypertension (elevated mean pulmonary arterial pressure with a normal pulmonary arterial wedge pressure and elevated pulmonary vascular resistance), followed by systematic exclusion of left heart disease, lung disease/hypoxia, chronic thromboembolic disease and the associated and drug- or toxin-induced Group 1 subtypes. Only after this exclusion cascade is the case designated idiopathic.

right heart catheterization NCIT:C80411

Show evidence (2 references)

DOI:10.3390/biomedicines13071773 SUPPORT Human Clinical

"The gold standard for diagnosis remains invasive right heart catheterization."

Establishes invasive haemodynamic confirmation as the diagnostic reference standard.

DOI:10.3390/biomedicines13071773 SUPPORT Human Clinical

"without other causes of pre-capillary hypertension such as lung diseases or chronic thromboembolic pulmonary hypertension"

Supports the requirement to exclude Group 3 and Group 4 pulmonary hypertension before designating disease idiopathic.

Transthoracic echocardiography

Echocardiography is the principal noninvasive screening and probability-assessment study. It evaluates right-heart structure and function and possible left-heart causes, but does not replace confirmatory right-heart catheterisation.

echocardiography NCIT:C16525

Show evidence (1 reference)

DOI:10.3390/biomedicines13071773 SUPPORT Human Clinical

"Along with invasive hemodynamic measurements, several noninvasive imaging modalities such as echocardiography and ventilation-perfusion scanning are key adjunct techniques."

Establishes echocardiography as a key noninvasive adjunct in the PAH diagnostic pathway.

Ventilation-perfusion scanning

Ventilation-perfusion scanning screens for chronic thromboembolic pulmonary hypertension, whose exclusion is mandatory before pre-capillary pulmonary hypertension can be designated idiopathic Group 1 PAH.

ventilation-perfusion scan NCIT:C38100

Show evidence (1 reference)

DOI:10.3390/biomedicines13071773 SUPPORT Human Clinical

"Along with invasive hemodynamic measurements, several noninvasive imaging modalities such as echocardiography and ventilation-perfusion scanning are key adjunct techniques."

Establishes ventilation-perfusion scanning as a key adjunct used to exclude the Group 4 chronic-thromboembolic mimic.

Pulmonary function testing with DLCO

Spirometry and diffusing-capacity measurement evaluate Group 3 lung disease and identify the low-DLCO IPAH lung phenotype. Normal or near-normal spirometry with severely reduced DLCO distinguishes that subtype from overt parenchymal lung disease.

pulmonary function test NCIT:C38081

Show evidence (1 reference)

PMID:35777416 SUPPORT Human Clinical

"Most patients with IPAH and a lung phenotype had normal or near normal spirometry, a severe reduction in DLCO, with the majority having no or a mild degree of parenchymal lung involvement on chest computed tomography."

Defines the pulmonary-function pattern that identifies the IPAH lung phenotype while helping exclude overt Group 3 disease.

Acute pulmonary vasodilator testing

Acute vasoreactivity testing during the diagnostic right-heart catheterisation identifies the small subgroup of IPAH patients who may benefit from long-term calcium-channel blockade. This test is applied specifically in idiopathic, heritable and drug-associated PAH, and is one of the few points at which IPAH management diverges from other PAH subtypes.

cardiac catheterization NCIT:C38044

Show evidence (1 reference)

PMID:15939821 SUPPORT Human Clinical

"Acute pulmonary vasodilator testing with epoprostenol or nitric oxide was performed in 557 IPAH patients."

Documents acute vasodilator testing as the standard procedure applied to IPAH patients to identify calcium-channel-blocker candidates.

Comprehensive PAH gene panel testing

Genetic testing with a curated PAH/PVOD gene panel including copy-number analysis is recommended for patients diagnosed with idiopathic PAH. A positive result reclassifies the patient as heritable PAH and enables cascade screening of relatives; a negative panel does not exclude genetic susceptibility.

genetic testing NCIT:C15709

Show evidence (2 references)

PMID:36302552 SUPPORT Human Clinical

"importantly through cascade screening, the detection of healthy causal variant carriers, to whom regular assessment should be offered."

The international consensus supports panel-based genetic testing with cascade screening of relatives.

PMID:39209481 SUPPORT Human Clinical

"Gene and variant curation by an expert panel now provides a robust framework for knowing which genes to test and how to interpret variants in clinical practice. We recommend that genetic testing be offered to specific subgroups of symptomatic patients with PAH"

Supports expert-curated gene-panel testing as current practice for symptomatic PAH subgroups, which include idiopathic disease.

📈

Progression

2

Insidious onset with diagnostic delay

Symptoms at onset (exertional dyspnoea, fatigue) are nonspecific, so IPAH is frequently recognised only at an advanced stage.

Show evidence (1 reference)

PMID:38797830 SUPPORT Human Clinical

"Idiopathic pulmonary arterial hypertension (IPAH) is a devastating pulmonary vascular disease characterized by a progressive increase in pulmonary vascular resistance and right heart failure"

Establishes the progressive, right-heart-directed natural history of IPAH.

Progressive obstructive vascular disease and right heart failure

Untreated disease is relentlessly progressive; the historical median survival in the pre-targeted-therapy era was 2.8 years. Modern pathway-directed therapy improves haemodynamics, function and prognosis but does not reverse the underlying vascular remodeling.

Show evidence (2 references)

PMID:37376028 SUPPORT Human Clinical

"In the era of non-targeted agents, PAH had a very dismal prognosis with a median survival time of only 2.8 years."

Documents the historical untreated natural history against which modern therapy is measured.

PMID:37376028 SUPPORT Human Clinical

"Current targeted agents delay the progression of PAH but cannot fundamentally reverse pulmonary vascular remodeling."

Supports the modelling of contemporary therapy as disease-modifying but not curative.

📊

Prevalence

3

United States

Point Prevalence 1.0 per 100,000 (0.5–1.5) 1–9 per 1,000,000

Reported as 5-15 cases of PAH per million individuals in the United States; IPAH is the largest single aetiological subgroup within PAH. Recorded here as the PAH-level estimate because IPAH-only population prevalence is not separately reported in the cited source.

Show evidence (1 reference)

PMID:37461108 SUPPORT Human Clinical

"of PAH to be between 5 and 15 cases per million individuals in the United States"

Provides the population occurrence band for PAH, within which IPAH is the dominant subgroup; the figure is PAH-wide rather than IPAH-specific, hence PARTIAL.

Idiopathic PAH patients across epidemiological studies

Unknown Unknown

Female predominance is a hallmark of IPAH, with a reported female-to-male incidence ratio of 4.1:1 in the IPAH category (4.3:1 across all PAH). Registry data show that this predominance is concentrated in classical IPAH and is substantially attenuated in the low-DLCO lung phenotype.

Show evidence (2 references)

PMID:37461108 SUPPORT Human Clinical

"women have a higher incidence rate than men across multiple studies (4.3:1 in the total PAH group and 4.1:1 in the IPAH category)"

Directly quantifies the female predominance of IPAH as distinct from PAH overall.

PMID:35777416 SUPPORT Human Clinical

"While 99 (77%) patients in COMPERA and 133 (72%) patients in ASPIRE with classical IPAH were female, there was a lower proportion of female patients in the IPAH and a lung phenotype cohort"

Shows that the female predominance of IPAH is concentrated in the classical phenotype and attenuated in the low-DLCO lung phenotype.

IPAH patients undergoing BMPR2 genetic testing

Unknown Unknown

Pooled across 24 studies of 3124 patients diagnosed with IPAH, 17.75% carried a pathogenic or likely pathogenic BMPR2 variant. This is the quantitative basis for treating the IPAH/heritable-PAH boundary as porous rather than absolute.

Show evidence (1 reference)

PMID:40229839 SUPPORT Human Clinical

"the frequency of P/LP variants in our cohort (10.48%) is lower than the overall average of 17.75% from the meta-analysis"

Provides a pooled estimate of pathogenic BMPR2 variant carriage among patients carrying an IPAH diagnosis.

🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from Idiopathic Pulmonary Arterial Hypertension:

Heritable pulmonary arterial hypertension MONDO:0017148

Overlapping Features Clinically and mechanistically indistinguishable from IPAH at presentation; the distinction rests entirely on family history or on identification of a pathogenic germline variant. Because penetrance is incomplete and sex-dependent, a substantial minority of apparently idiopathic patients are genetically heritable.

Distinguishing Features

A pathogenic or likely pathogenic germline variant in a curated PAH gene reclassifies IPAH as heritable PAH.
Pooled genetic testing finds pathogenic BMPR2 variants in roughly 18% of patients diagnosed as IPAH.
Family history may be absent in genetically heritable disease because of incomplete, age- and sex-dependent penetrance.

Show evidence (1 reference)

PMID:36302552 SUPPORT Human Clinical

"Benefits of including molecular genetic testing within the management protocol of patients with PAH include the identification of individuals misclassified by other diagnostic approaches"

Supports genetic testing as the discriminator between idiopathic and heritable PAH.

Drug- or toxin-induced pulmonary arterial hypertension MONDO:0017149

Overlapping Features Group 1 PAH attributable to a culprit exposure. Exposure history is the sole discriminator; the downstream vascular pathology is shared.

Distinguishing Features

A documented exposure to a definite PAH-associated drug or toxin (anorexigens, methamphetamine, dasatinib) excludes the idiopathic designation.
Some drug-induced disease is partly reversible after withdrawal of the culprit agent, which has no counterpart in IPAH.

Pulmonary hypertension due to lung disease or hypoxia Not Yet Curated MONDO:0017157

Overlapping Features WHO Group 3 pulmonary hypertension. The IPAH lung phenotype (low DLCO, smoking history) sits at the boundary: these patients satisfy IPAH haemodynamic and spirometric criteria but resemble Group 3 disease in age, sex distribution, and poor treatment response.

Distinguishing Features

Group 3 disease has overt obstructive or restrictive lung disease; the IPAH lung phenotype has normal or near-normal spirometry with little parenchymal involvement on CT.
Response to PAH therapy is poor in both the IPAH lung phenotype and Group 3 pulmonary hypertension, and markedly better in classical IPAH.

Show evidence (1 reference)

PMID:35777416 SUPPORT Human Clinical

"Improvements in WHO functional class were observed in 54% of patients with classical IPAH, 26% of patients with IPAH with a lung phenotype, and 22% of patients with group 3 pulmonary hypertension"

Quantifies the therapeutic behaviour that places the IPAH lung phenotype closer to Group 3 disease than to classical IPAH.

Pulmonary veno-occlusive disease and/or pulmonary capillary haemangiomatosis MONDO:0018554

Overlapping Features A venous and capillary pulmonary vasculopathy that can mimic IPAH haemodynamically but is managed differently and can decompensate on PAH vasodilators. Biallelic EIF2AK4 variants identify heritable cases.

Distinguishing Features

Biallelic EIF2AK4 variants indicate PVOD/PCH rather than ordinary IPAH and materially alter management.
Characteristic CT findings and a very low DLCO with hypoxaemia suggest PVOD/PCH.

Show evidence (1 reference)

PMID:29650961 SUPPORT Human Clinical

"Fourteen cases (1.3%) with biallelic EIF2AK4 mutations were found"

Shows that biallelic EIF2AK4 (PVOD/PCH) cases are recovered from cohorts recruited as idiopathic and heritable PAH, making PVOD/PCH an important differential.

🔬

Clinical Trials

1

NCT04576988 PHASE_III

STELLAR, the randomised placebo-controlled phase 3 trial of sotatercept added to background PAH therapy, with 6-minute walk distance as the primary endpoint.

Target Phenotypes: Exercise intolerance HP:0003546

Show evidence (1 reference)

clinicaltrials:NCT04576988 SUPPORT Human Clinical

"The primary hypothesis of the study is that the participants receiving sotatercept will have improved 6-minute walk distance (6MWD) at 24 weeks compared to participants receiving placebo."

ClinicalTrials.gov describes STELLAR's exercise-capacity primary endpoint.

{ }

Source YAML

click to show

name: Idiopathic Pulmonary Arterial Hypertension
creation_date: "2026-08-01T18:30:00Z"
category: Complex
disease_term:
  preferred_term: idiopathic pulmonary arterial hypertension
  term:
    id: MONDO:0001999
    label: idiopathic pulmonary arterial hypertension
parents:
- Pulmonary arterial hypertension
description: >-
  Idiopathic pulmonary arterial hypertension (IPAH) is the sporadic form of WHO
  Group 1 pulmonary arterial hypertension: pre-capillary pulmonary hypertension
  confirmed by right-heart catheterisation in which no associated condition, no
  culprit drug or toxin exposure, and no family history of pulmonary arterial
  hypertension can be identified. It is therefore defined jointly by positive
  haemodynamic findings and by exclusion of Groups 2-5 pulmonary hypertension
  and of the associated and drug- or toxin-induced Group 1 subtypes. "Idiopathic"
  denotes an unidentified cause, not an absent one: once vascular disease is
  established, IPAH converges on the same obstructive pulmonary vascular
  remodeling cascade shared with heritable and associated PAH, and a meaningful
  minority of patients labelled idiopathic are found on genetic testing to carry
  a rare pathogenic variant (most often in BMPR2), which reclassifies them as
  heritable PAH. IPAH shows a marked female predominance and, in modern
  registries, is clinically heterogeneous - spanning classical young, largely
  female disease, an older low-diffusing-capacity smoking-associated lung
  phenotype, and a small acutely vasoreactive subgroup with durable
  calcium-channel-blocker response.
synonyms:
- IPAH
- Idiopathic PAH
- Primary pulmonary hypertension
- Primary pulmonary arterial hypertension
- Sporadic primary pulmonary hypertension
classifications:
  harrisons_chapter:
  - classification_value: CARDIOVASCULAR
    evidence:
    - reference: DOI:10.3390/biomedicines13071773
      reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Pulmonary arterial hypertension (PAH) is a specific subset of PH characterized by a normal pulmonary arterial wedge pressure (PAWP), combined with elevated mPAP and increased pulmonary vascular resistance (PVR)
      explanation: >-
        PAH is defined by pulmonary vascular haemodynamics and culminates in right heart
        failure, placing IPAH in Harrison's cardiovascular Part.
  - classification_value: RESPIRATORY
    evidence:
    - reference: PMID:38797830
      reference_title: A new integrative analysis of histopathology and single cell RNA-seq reveals the CCL5 mediated T and NK cell interaction with vascular cells in idiopathic pulmonary arterial hypertension.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Accumulation of immune cells in remodeled pulmonary arterioles is a common finding in IPAH lung tissue
      explanation: >-
        The primary lesion of IPAH is in the pulmonary arterial circulation within lung tissue,
        so the entry also belongs to Harrison's respiratory Part.
has_subtypes:
- name: Classical IPAH
  display_name: Classical IPAH (no cardiopulmonary comorbidities, preserved DLCO)
  description: >-
    The canonical IPAH phenotype: younger, predominantly female patients without
    cardiopulmonary comorbidities and with a diffusing capacity for carbon monoxide
    (DLCO) of 45% predicted or more. This subgroup shows the largest treatment
    response to PAH pathway therapy.
  evidence:
  - reference: PMID:35777416
    reference_title: "Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      patients with classical IPAH (defined by the absence of cardiopulmonary comorbidities and a DLCO of 45% or more predicted)
    explanation: >-
      The COMPERA/ASPIRE registry analysis defines classical IPAH explicitly by absence of
      cardiopulmonary comorbidities and preserved DLCO.
- name: Lung phenotype IPAH
  display_name: IPAH with a lung phenotype (low DLCO, smoking history)
  description: >-
    An emerging IPAH subgroup that meets diagnostic criteria for IPAH but has a
    severely reduced DLCO (<45% predicted) and a smoking history, with normal or
    near-normal spirometry and little or no parenchymal lung disease on CT. These
    patients are older, far less female-predominant, and respond poorly to PAH
    therapy, resembling Group 3 pulmonary hypertension more than classical IPAH.
  evidence:
  - reference: PMID:35777416
    reference_title: "Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Among patients meeting diagnostic criteria for idiopathic pulmonary arterial hypertension (IPAH), there is an emerging lung phenotype characterised by a low diffusion capacity for carbon monoxide (DLCO) and a smoking history.
    explanation: >-
      This directly establishes the low-DLCO smoking-associated lung phenotype as a distinct
      subgroup within diagnostically defined IPAH.
  - reference: PMID:35777416
    reference_title: "Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most patients with IPAH and a lung phenotype had normal or near normal spirometry, a severe reduction in DLCO, with the majority having no or a mild degree of parenchymal lung involvement on chest computed tomography.
    explanation: >-
      Characterises the physiological and radiological signature that separates this subgroup
      from Group 3 pulmonary hypertension due to overt lung disease.
- name: Vasoresponder IPAH
  display_name: Acutely vasoreactive, long-term calcium-channel-blocker-responsive IPAH
  description: >-
    A small IPAH subgroup identified by acute pulmonary vasodilator testing at
    diagnostic right-heart catheterisation. Roughly one in eight IPAH patients is an
    acute responder, but fewer than 10% sustain long-term benefit on calcium-channel
    blocker monotherapy. Long-term responders have an excellent prognosis, making
    vasoreactivity testing a distinctive and clinically decisive step in IPAH (and
    heritable/drug-associated PAH) that is not applied across other PH groups.
  evidence:
  - reference: PMID:15939821
    reference_title: Long-term response to calcium channel blockers in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Among the 70 patients who displayed acute pulmonary vasoreactivity (12.6%; 95% CI, 9.8% to 15.3%) and received CCB therapy, only 38 showed long-term improvement (6.8%; 95% CI, 4.7% to 8.9%).
    explanation: >-
      Quantifies both the acute-vasoreactive and the durable calcium-channel-blocker-responsive
      fractions of an IPAH referral cohort.
  - reference: PMID:15939821
    reference_title: Long-term response to calcium channel blockers in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Long-term CCB responders represent <10% of IPAH patients evaluated in a pulmonary vascular referral center.
    explanation: >-
      Establishes the small size of the durable vasoresponder subgroup within IPAH.
prevalence:
- population: United States
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_9_PER_1000000
  rate_per_100000: 1.0
  rate_low: 0.5
  rate_high: 1.5
  notes: >-
    Reported as 5-15 cases of PAH per million individuals in the United States;
    IPAH is the largest single aetiological subgroup within PAH. Recorded here as
    the PAH-level estimate because IPAH-only population prevalence is not separately
    reported in the cited source.
  evidence:
  - reference: PMID:37461108
    reference_title: "Unraveling the epigenetic landscape of pulmonary arterial hypertension: implications for personalized medicine development."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      of PAH to be between 5 and 15 cases per million individuals in the United States
    explanation: >-
      Provides the population occurrence band for PAH, within which IPAH is the dominant
      subgroup; the figure is PAH-wide rather than IPAH-specific, hence PARTIAL.
- population: Idiopathic PAH patients across epidemiological studies
  measure_type: UNKNOWN
  prevalence_class: UNKNOWN
  notes: >-
    Female predominance is a hallmark of IPAH, with a reported female-to-male
    incidence ratio of 4.1:1 in the IPAH category (4.3:1 across all PAH). Registry
    data show that this predominance is concentrated in classical IPAH and is
    substantially attenuated in the low-DLCO lung phenotype.
  evidence:
  - reference: PMID:37461108
    reference_title: "Unraveling the epigenetic landscape of pulmonary arterial hypertension: implications for personalized medicine development."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      women have a higher incidence rate than men across multiple studies (4.3:1 in the total PAH group and 4.1:1 in the IPAH category)
    explanation: >-
      Directly quantifies the female predominance of IPAH as distinct from PAH overall.
  - reference: PMID:35777416
    reference_title: "Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      While 99 (77%) patients in COMPERA and 133 (72%) patients in ASPIRE with classical IPAH were female, there was a lower proportion of female patients in the IPAH and a lung phenotype cohort
    explanation: >-
      Shows that the female predominance of IPAH is concentrated in the classical phenotype
      and attenuated in the low-DLCO lung phenotype.
- population: IPAH patients undergoing BMPR2 genetic testing
  measure_type: UNKNOWN
  prevalence_class: UNKNOWN
  notes: >-
    Pooled across 24 studies of 3124 patients diagnosed with IPAH, 17.75% carried a
    pathogenic or likely pathogenic BMPR2 variant. This is the quantitative basis for
    treating the IPAH/heritable-PAH boundary as porous rather than absolute.
  evidence:
  - reference: PMID:40229839
    reference_title: "The prevalence of pathogenic variants in the BMPR2 gene in patients with the idiopathic pulmonary arterial hypertension in the Russian population: sequencing data and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the frequency of P/LP variants in our cohort (10.48%) is lower than the overall average of 17.75% from the meta-analysis
    explanation: >-
      Provides a pooled estimate of pathogenic BMPR2 variant carriage among patients carrying
      an IPAH diagnosis.
progression:
- phase: Insidious onset with diagnostic delay
  notes: >-
    Symptoms at onset (exertional dyspnoea, fatigue) are nonspecific, so IPAH is
    frequently recognised only at an advanced stage.
  evidence:
  - reference: PMID:38797830
    reference_title: A new integrative analysis of histopathology and single cell RNA-seq reveals the CCL5 mediated T and NK cell interaction with vascular cells in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Idiopathic pulmonary arterial hypertension (IPAH) is a devastating pulmonary vascular disease characterized by a progressive increase in pulmonary vascular resistance and right heart failure
    explanation: >-
      Establishes the progressive, right-heart-directed natural history of IPAH.
- phase: Progressive obstructive vascular disease and right heart failure
  notes: >-
    Untreated disease is relentlessly progressive; the historical median survival in
    the pre-targeted-therapy era was 2.8 years. Modern pathway-directed therapy
    improves haemodynamics, function and prognosis but does not reverse the
    underlying vascular remodeling.
  evidence:
  - reference: PMID:37376028
    reference_title: "Medical Management of Pulmonary Arterial Hypertension: Current Approaches and Investigational Drugs."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the era of non-targeted agents, PAH had a very dismal prognosis with a median survival time of only 2.8 years.
    explanation: >-
      Documents the historical untreated natural history against which modern therapy is
      measured.
  - reference: PMID:37376028
    reference_title: "Medical Management of Pulmonary Arterial Hypertension: Current Approaches and Investigational Drugs."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Current targeted agents delay the progression of PAH but cannot fundamentally reverse pulmonary vascular remodeling.
    explanation: >-
      Supports the modelling of contemporary therapy as disease-modifying but not curative.
pathophysiology:
- name: Unidentified Initiating Insult in a Susceptible Pulmonary Vasculature
  biological_scale: ORGANISM
  role: trigger
  description: >-
    The defining feature of IPAH is that no associated condition, drug or toxin
    exposure, or family history explains the disease after a complete evaluation.
    This is an epistemic rather than a biological null: IPAH is best modelled as a
    threshold disorder in which incompletely characterised genetic susceptibility,
    epigenetic dysregulation, sex-hormone biology and acquired vascular stresses
    combine to cross a disease threshold, with no single trigger identifiable in the
    individual patient. This node substitutes for the disorder-specific trigger that
    heritable PAH (a germline BMPR2-pathway lesion) and drug- or toxin-induced PAH
    (a culprit exposure) each supply, and it is the reason IPAH is a diagnosis of
    exclusion.
  locations:
  - preferred_term: pulmonary artery
    term:
      id: UBERON:0002012
      label: pulmonary artery
  evidence:
  - reference: DOI:10.3390/biomedicines13071773
    reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The majority of PAH cases are idiopathic; other common etiologies include connective tissue disease-associated PAH, congenital heart disease, and portopulmonary hypertension.
    explanation: >-
      Confirms that idiopathic disease - PAH without an identified associated cause - is the
      largest aetiological category within Group 1 PAH.
  - reference: PMID:36302552
    reference_title: "Genetic counselling and testing in pulmonary arterial hypertension: a consensus statement on behalf of the International Consortium for Genetic Studies in PAH."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pulmonary arterial hypertension (PAH) is a rare disease that can be caused by (likely) pathogenic germline genomic variants.
    explanation: >-
      Supports that an aetiological cause may be latent rather than absent in patients
      initially designated idiopathic; PARTIAL because the statement is PAH-wide.
  downstream:
  - target: Pulmonary Arterial Endothelial Dysfunction
    description: >-
      Whatever the unresolved initiating insult, the earliest identifiable lesion in
      IPAH is dysfunction of the pulmonary arterial endothelium.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: Occult Rare Variant Burden and Reclassification to Heritable PAH
  biological_scale: MOLECULAR
  role: modifier
  description: >-
    A substantial minority of patients who satisfy IPAH criteria are subsequently
    found on comprehensive PAH gene-panel or genome sequencing to carry a rare
    pathogenic or likely pathogenic germline variant - most often a loss-of-function
    BMPR2 allele, and less often variants in TBX4, ATP13A3, SOX17, GDF2, AQP1 or
    other curated PAH genes. Because incomplete, age- and sex-dependent penetrance
    means many carriers have no affected relative, absence of family history does not
    exclude a germline cause. Detecting such a variant reclassifies the patient as
    heritable PAH and opens cascade screening of relatives. This node is the explicit
    mechanistic boundary between this entry and Heritable Pulmonary Arterial
    Hypertension: it is not a separate remodeling mechanism but a statement that a
    fraction of the IPAH population is misclassified heritable disease.
  evidence:
  - reference: PMID:40229839
    reference_title: "The prevalence of pathogenic variants in the BMPR2 gene in patients with the idiopathic pulmonary arterial hypertension in the Russian population: sequencing data and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A meta-analysis, performed with MOOSE, included 24 studies involving 3124 IPAH patients and 470 P/LP variants.
    explanation: >-
      Establishes the scale of the pooled IPAH genetic-testing evidence underpinning this node.
  - reference: PMID:40229839
    reference_title: "The prevalence of pathogenic variants in the BMPR2 gene in patients with the idiopathic pulmonary arterial hypertension in the Russian population: sequencing data and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Analysis of 105 adult IPAH patients in Russia revealed 11 patients (10.48%) as carriers of pathogenic or likely pathogenetic (P/LP) BMPR2 variants.
    explanation: >-
      Directly documents occult pathogenic BMPR2 carriage within a clinically diagnosed IPAH
      cohort.
  - reference: PMID:36302552
    reference_title: "Genetic counselling and testing in pulmonary arterial hypertension: a consensus statement on behalf of the International Consortium for Genetic Studies in PAH."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Benefits of including molecular genetic testing within the management protocol of patients with PAH include the identification of individuals misclassified by other diagnostic approaches
    explanation: >-
      The international consensus explicitly frames genetic testing as a means of correcting
      misclassification, the mechanism modelled by this node.
  downstream:
  - target: Pulmonary Arterial Endothelial Dysfunction
    description: >-
      In the variant-positive fraction, reduced BMP receptor signalling is the
      identifiable molecular cause of the endothelial lesion, as in heritable PAH.
    causal_link_type: DIRECT
- name: Pulmonary Arterial Endothelial Dysfunction
  conforms_to: "pulmonary_vascular_remodeling#Pulmonary Endothelial Dysfunction and Impaired BMP Signaling"
  biological_scale: CELLULAR
  role: trigger
  description: >-
    Pulmonary arterial endothelial cells lose homeostatic function: BMP receptor
    signalling is reduced (by germline lesion in the occult-variant fraction, and by
    acquired suppression otherwise), nitric-oxide and prostacyclin production fall
    while endothelin-1 rises, barrier integrity is lost, and an apoptosis-prone
    population is replaced by apoptosis-resistant, hyperproliferative cells. This is
    the conserved entry point into the shared pulmonary vascular remodeling module;
    IPAH substitutes an unidentified or occult-genetic insult for the germline BMPR2
    lesion of heritable PAH.
  cell_types:
  - preferred_term: pulmonary artery endothelial cell
    term:
      id: CL:1001568
      label: pulmonary artery endothelial cell
  locations:
  - preferred_term: pulmonary artery
    term:
      id: UBERON:0002012
      label: pulmonary artery
  biological_processes:
  - preferred_term: BMP signaling pathway
    term:
      id: GO:0030509
      label: BMP signaling pathway
    modifier: DECREASED
  - preferred_term: nitric oxide biosynthetic process
    term:
      id: GO:0006809
      label: nitric oxide biosynthetic process
    modifier: DECREASED
  - preferred_term: endothelin receptor signaling pathway
    term:
      id: GO:0086100
      label: endothelin receptor signaling pathway
    modifier: INCREASED
  evidence:
  - reference: PMID:36603064
    reference_title: BMPR2 Mutation and Metabolic Reprogramming in Pulmonary Arterial Hypertension.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Compelling evidence from animal models suggests endothelial cell dysfunction is a key initial trigger of pulmonary vascular remodeling, which is characterised by hyperproliferation and early apoptosis followed by enrichment of apoptosis-resistant populations.
    explanation: >-
      Establishes endothelial dysfunction as the conserved initiating cellular lesion of
      pulmonary vascular remodeling. Evidence source is OTHER because this is a review
      synthesising animal-model and human data.
  - reference: DOI:10.3390/biomedicines13071773
    reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The pathophysiology of PAH involves the following four primary pathways: nitric oxide, endothelin-1, prostacyclin, and activin/bone morphogenetic protein (BMP).
    explanation: >-
      Names the four endothelium-centred signalling axes whose imbalance defines this node and
      which the approved therapies target.
  downstream:
  - target: Pulmonary Artery Smooth Muscle Cell Proliferation and Vasoconstriction
    description: >-
      Loss of endothelium-derived vasodilator and antiproliferative signalling
      releases the medial smooth muscle compartment.
    causal_link_type: DIRECT
  - target: T and NK Cell CCL5-Mediated Immune-Vascular Crosstalk
    description: >-
      Injured endothelium participates in chemokine-mediated recruitment of
      lymphoid cells to the pulmonary vascular wall.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: T and NK Cell CCL5-Mediated Immune-Vascular Crosstalk
  biological_scale: CELLULAR
  role: amplifier
  description: >-
    Integrated analysis of IPAH lung transcriptomes, histopathology scoring and
    single-cell RNA sequencing identifies CXCL9, CCL5, GZMA and GZMK as
    inflammation-associated hub genes distinguishing IPAH lungs from controls, with
    CCL5 and GZMA expressed predominantly by T and NK cells. CCL5 mediates
    interaction of these lymphoid populations with pulmonary endothelial cells,
    smooth muscle cells and fibroblasts through multiple receptors, defining an
    adaptive immune-vascular amplification arm of IPAH remodeling. This is an
    IPAH-specific refinement of the generic perivascular-inflammation theme; it is
    discovery-stage and not a validated clinical target.
  cell_types:
  - preferred_term: T cell
    term:
      id: CL:0000084
      label: T cell
  - preferred_term: natural killer cell
    term:
      id: CL:0000623
      label: natural killer cell
  locations:
  - preferred_term: pulmonary artery
    term:
      id: UBERON:0002012
      label: pulmonary artery
  biological_processes:
  - preferred_term: inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
    modifier: INCREASED
  evidence:
  - reference: PMID:38797830
    reference_title: A new integrative analysis of histopathology and single cell RNA-seq reveals the CCL5 mediated T and NK cell interaction with vascular cells in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Through an extensive bioinformatics analysis, CXCL9, CCL5, GZMA and GZMK were identified as hub genes that distinguished IPAH patients from controls.
    explanation: >-
      Identifies the IPAH-specific inflammatory hub genes underpinning this node from human
      IPAH lung transcriptomes.
  - reference: PMID:38797830
    reference_title: A new integrative analysis of histopathology and single cell RNA-seq reveals the CCL5 mediated T and NK cell interaction with vascular cells in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      only CCL5 and GZMA were highly expressed in T and NK cells, where CCL5 mediated T and NK cell interaction with endothelial cells, smooth muscle cells, and fibroblasts through multiple receptors.
    explanation: >-
      Directly supports the CCL5-mediated lymphoid-to-vascular-cell interaction that defines
      this amplifier node.
  downstream:
  - target: Pulmonary Artery Smooth Muscle Cell Proliferation and Vasoconstriction
    description: >-
      Chemokine-mediated immune-vascular crosstalk amplifies the proliferative
      response of the medial smooth muscle compartment.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
- name: Pulmonary Artery Smooth Muscle Cell Proliferation and Vasoconstriction
  conforms_to: "pulmonary_vascular_remodeling#Pulmonary Artery Smooth Muscle Cell Proliferation and Vasoconstriction"
  biological_scale: CELLULAR
  role: amplifier
  description: >-
    Paracrine signals from the dysfunctional endothelium, compounded by
    inflammatory input, drive a proliferative, migratory and apoptosis-resistant
    phenotype in pulmonary artery smooth muscle cells, together with sustained
    vasoconstriction. In the small acutely vasoreactive IPAH subgroup, the
    vasoconstrictive component still dominates over fixed remodeling, which is why
    those patients respond durably to calcium-channel blockade.
  cell_types:
  - preferred_term: pulmonary artery smooth muscle cell
    term:
      id: CL:0002591
      label: smooth muscle cell of the pulmonary artery
  locations:
  - preferred_term: pulmonary artery
    term:
      id: UBERON:0002012
      label: pulmonary artery
  biological_processes:
  - preferred_term: smooth muscle cell proliferation
    term:
      id: GO:0048659
      label: smooth muscle cell proliferation
    modifier: INCREASED
  - preferred_term: resistance to apoptosis
    term:
      id: GO:0043066
      label: negative regulation of apoptotic process
    modifier: INCREASED
  - preferred_term: vasoconstriction
    term:
      id: GO:0042310
      label: vasoconstriction
    modifier: INCREASED
  evidence:
  - reference: PMID:37461108
    reference_title: "Unraveling the epigenetic landscape of pulmonary arterial hypertension: implications for personalized medicine development."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Multiple biological processes, such as smooth muscle proliferation, endothelial dysfunction, inflammation, and resistance to apoptosis, are associated with PAH.
    explanation: >-
      Names smooth muscle proliferation and apoptosis resistance as core processes of the PAH
      remodeling cascade this node represents.
  - reference: PMID:39421926
    reference_title: Ferroptosis-Mediated Inflammation Promotes Pulmonary Hypertension.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Ferroptotic pulmonary arterial endothelial cell damage-associated molecular patterns restructured the transcriptomic signature and mitochondrial morphology, promoted the proliferation of pulmonary artery smooth muscle cells, and created a proinflammatory phenotype in monocytes in vitro.
    explanation: >-
      Provides a specific in vitro demonstration that injured endothelium drives smooth muscle
      proliferation; PARTIAL because the mechanism (ferroptotic DAMPs) is one of several
      routes and is not IPAH-specific.
  downstream:
  - target: Obstructive Pulmonary Vascular Remodeling
    description: >-
      Medial expansion and muscularisation of peripheral arterioles narrow the
      pulmonary vascular lumen.
    causal_link_type: DIRECT
- name: Obstructive Pulmonary Vascular Remodeling
  conforms_to: "pulmonary_vascular_remodeling#Obstructive Pulmonary Vascular Remodeling"
  biological_scale: TISSUE
  role: central_effector
  description: >-
    Sustained smooth muscle proliferation, adventitial fibroblast activation, matrix
    deposition and neointima formation remodel the wall of small pulmonary arteries,
    producing medial hypertrophy, eccentric and concentric intimal fibrosis,
    in-situ thrombosis and plexiform lesions that obliterate the lumen. This
    structural obstruction is the central effector shared with heritable, associated
    and drug- or toxin-induced PAH, and it is largely irreversible once established.
  cell_types:
  - preferred_term: pulmonary artery smooth muscle cell
    term:
      id: CL:0002591
      label: smooth muscle cell of the pulmonary artery
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  locations:
  - preferred_term: pulmonary artery
    term:
      id: UBERON:0002012
      label: pulmonary artery
  biological_processes:
  - preferred_term: blood vessel remodeling
    term:
      id: GO:0001974
      label: blood vessel remodeling
    modifier: DYSREGULATED
  - preferred_term: extracellular matrix organization
    term:
      id: GO:0030198
      label: extracellular matrix organization
    modifier: ABNORMAL
  evidence:
  - reference: PMID:38797830
    reference_title: A new integrative analysis of histopathology and single cell RNA-seq reveals the CCL5 mediated T and NK cell interaction with vascular cells in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      is central to the irreversible progression of IPAH
    explanation: >-
      IPAH-specific statement that pulmonary vascular remodeling, marked by arteriolar
      eccentricity and occlusive intimal thickening, is the central and largely irreversible
      driver of disease progression.
  - reference: PMID:29650961
    reference_title: Identification of rare sequence variation underlying heritable pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Idiopathic and heritable pulmonary arterial hypertension (PAH) are rare disorders characterised by occlusion of arterioles in the lung
    explanation: >-
      Explicitly groups idiopathic with heritable PAH around the shared lesion of arteriolar
      occlusion, the basis for conformance to the shared module.
  downstream:
  - target: Increased Pulmonary Vascular Resistance
    description: >-
      Fixed luminal obstruction, added to dynamic vasoconstriction, raises resistance
      across the pulmonary bed.
    causal_link_type: DIRECT
- name: Increased Pulmonary Vascular Resistance
  conforms_to: "pulmonary_vascular_remodeling#Increased Pulmonary Vascular Resistance"
  biological_scale: ORGANISM
  role: effector
  description: >-
    The combination of fixed structural obstruction and sustained vasoconstriction
    raises pulmonary vascular resistance and reduces pulmonary arterial compliance,
    while pulmonary arterial wedge pressure remains normal - the pre-capillary
    haemodynamic signature confirmed at right-heart catheterisation that defines PAH
    and separates it from Group 2 pulmonary hypertension due to left heart disease.
  biological_processes:
  - preferred_term: vasoconstriction
    term:
      id: GO:0042310
      label: vasoconstriction
    modifier: INCREASED
  evidence:
  - reference: DOI:10.3390/biomedicines13071773
    reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pulmonary arterial hypertension (PAH) is a specific subset of PH characterized by a normal pulmonary arterial wedge pressure (PAWP), combined with elevated mPAP and increased pulmonary vascular resistance (PVR), without other causes of pre-capillary hypertension such as lung diseases or chronic thromboembolic pulmonary hypertension.
    explanation: >-
      Defines the pre-capillary haemodynamic state of this node and its explicit exclusion of
      Group 3 and Group 4 pulmonary hypertension.
  downstream:
  - target: Precapillary Pulmonary Arterial Hypertension with Right Ventricular Failure
    description: >-
      Elevated resistance imposes a chronic pressure load on the right ventricle.
    causal_link_type: DIRECT
- name: Precapillary Pulmonary Arterial Hypertension with Right Ventricular Failure
  conforms_to: "pulmonary_vascular_remodeling#Pulmonary Arterial Hypertension"
  biological_scale: ORGANISM
  role: consequence
  description: >-
    Sustained elevation of pulmonary arterial pressure imposes chronic pressure
    overload on the right ventricle. Hypertrophy compensates initially, but
    ischaemia, fibrosis, dilation and tricuspid regurgitation eventually reduce
    right ventricular output, producing systemic venous congestion, exertional
    syncope and death from right heart failure.
  locations:
  - preferred_term: heart right ventricle
    term:
      id: UBERON:0002080
      label: heart right ventricle
  biological_processes:
  - preferred_term: right ventricular hypertrophy
    term:
      id: GO:0003300
      label: cardiac muscle hypertrophy
    modifier: INCREASED
  evidence:
  - reference: DOI:10.3390/biomedicines13071773
    reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dysregulation of these pathways leads to a progressive vasculopathy marked by vasoconstriction, vascular proliferation, elevated right heart afterload, and ultimately right-sided heart failure.
    explanation: >-
      Directly supports the terminal right-ventricular consequence of the remodeling cascade.
  - reference: PMID:38797830
    reference_title: A new integrative analysis of histopathology and single cell RNA-seq reveals the CCL5 mediated T and NK cell interaction with vascular cells in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Idiopathic pulmonary arterial hypertension (IPAH) is a devastating pulmonary vascular disease characterized by a progressive increase in pulmonary vascular resistance and right heart failure
    explanation: >-
      IPAH-specific confirmation that rising pulmonary vascular resistance culminates in right
      heart failure.
  downstream:
  - target: Exertional dyspnea
    description: Reduced cardiac output reserve produces exertional breathlessness.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - reduced cardiac output reserve
  - target: Exertional syncope
    description: Inability to raise cardiac output during exertion causes syncope.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - impaired cardiac output reserve
  - target: Right ventricular failure
    description: Maladaptive right ventricular remodeling culminates in overt failure.
    causal_link_type: DIRECT
  - target: Peripheral edema
    description: Right-heart congestion raises systemic venous pressure.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - systemic venous congestion
mechanistic_hypotheses:
- hypothesis_group_id: ipah_ferroptosis_inflammation
  hypothesis_label: Endothelial ferroptosis as an upstream inflammatory driver of IPAH remodeling
  description: >-
    An emerging model in which lipid peroxidation and ferroptotic death of pulmonary
    arterial endothelial cells release damage-associated molecular patterns that
    activate complement, recruit inflammatory macrophages and drive smooth muscle
    proliferation. Multi-omic and genetic-association data in humans plus rescue by
    the ferroptosis inhibitor ferrostatin-1 in monocrotaline rats support the model,
    but the evidence is preclinical for therapy and derives from PAH broadly rather
    than IPAH specifically.
  status: EMERGING
  evidence:
  - reference: PMID:39421926
    reference_title: Ferroptosis-Mediated Inflammation Promotes Pulmonary Hypertension.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Ferrostatin-1, a small-molecule ferroptosis inhibitor, mitigated PAH severity in monocrotaline rats.
    explanation: >-
      Provides the in vivo pharmacological rescue that anchors the ferroptosis hypothesis.
  - reference: PMID:39421926
    reference_title: Ferroptosis-Mediated Inflammation Promotes Pulmonary Hypertension.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Ferroptosis promotes PAH through metabolic and inflammatory mechanisms in the pulmonary vasculature.
    explanation: >-
      States the hypothesis in the authors' own terms. Evidence source is OTHER because the
      conclusion integrates human multi-omic, rodent and in vitro data.
phenotypes:
- category: Cardiovascular
  name: Pulmonary arterial hypertension
  diagnostic: true
  description: >-
    Pre-capillary pulmonary arterial hypertension confirmed by right-heart
    catheterisation is the defining phenotype; in IPAH it is present without an
    identifiable associated cause.
  phenotype_term:
    preferred_term: Pulmonary arterial hypertension
    term:
      id: HP:0002092
      label: Pulmonary arterial hypertension
  evidence:
  - reference: DOI:10.3390/biomedicines13071773
    reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pulmonary arterial hypertension (PAH) is a specific subset of PH characterized by a normal pulmonary arterial wedge pressure (PAWP), combined with elevated mPAP and increased pulmonary vascular resistance (PVR)
    explanation: >-
      Establishes the defining haemodynamic phenotype.
- category: Cardiovascular
  name: Increased pulmonary vascular resistance
  diagnostic: true
  description: >-
    An elevated pulmonary vascular resistance measured at right-heart
    catheterisation is required for the diagnosis and rises progressively over the
    disease course.
  phenotype_term:
    preferred_term: Increased pulmonary vascular resistance
    term:
      id: HP:0005317
      label: Increased pulmonary vascular resistance
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:38797830
    reference_title: A new integrative analysis of histopathology and single cell RNA-seq reveals the CCL5 mediated T and NK cell interaction with vascular cells in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Idiopathic pulmonary arterial hypertension (IPAH) is a devastating pulmonary vascular disease characterized by a progressive increase in pulmonary vascular resistance and right heart failure
    explanation: >-
      IPAH-specific description of progressively increasing pulmonary vascular resistance.
- category: Respiratory
  name: Exertional dyspnea
  description: >-
    Progressive breathlessness on exertion is the usual presenting symptom and is
    nonspecific, contributing to diagnostic delay.
  phenotype_term:
    preferred_term: Exertional dyspnea
    term:
      id: HP:0002875
      label: Exertional dyspnea
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:29540357
    reference_title: "Pulmonary arterial hypertension: pathogenesis and clinical management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients with PAH have dyspnea, reduced exercise capacity, exertional syncope, and premature death from right ventricular failure.
    explanation: >-
      Lists dyspnoea among the cardinal manifestations of PAH.
- category: Constitutional
  name: Fatigue
  description: Fatigue reflects the low cardiac-output reserve of advancing pulmonary vascular disease.
  phenotype_term:
    preferred_term: Fatigue
    term:
      id: HP:0012378
      label: Fatigue
  evidence:
  - reference: DOI:10.1183/13993003.01325-2024
    reference_title: Treatment algorithm for pulmonary arterial hypertension
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pulmonary arterial hypertension leads to significant impairment in haemodynamics, right heart function, exercise capacity, quality of life and survival.
    explanation: >-
      Supports impaired exercise capacity and quality of life; fatigue is the symptom-level
      expression, hence PARTIAL.
- category: Constitutional
  name: Exercise intolerance
  description: Reduced exercise capacity, quantified by 6-minute walk distance, is a core prognostic variable in IPAH.
  phenotype_term:
    preferred_term: Exercise intolerance
    term:
      id: HP:0003546
      label: Exercise intolerance
  evidence:
  - reference: PMID:29540357
    reference_title: "Pulmonary arterial hypertension: pathogenesis and clinical management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients with PAH have dyspnea, reduced exercise capacity, exertional syncope, and premature death from right ventricular failure.
    explanation: >-
      Directly supports reduced exercise capacity as a cardinal PAH manifestation.
- category: Cardiovascular
  name: Exertional syncope
  description: >-
    Syncope on exertion signals inability to augment cardiac output and marks
    advanced disease with adverse prognosis.
  phenotype_term:
    preferred_term: Syncope
    term:
      id: HP:0001279
      label: Syncope
  evidence:
  - reference: PMID:29540357
    reference_title: "Pulmonary arterial hypertension: pathogenesis and clinical management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients with PAH have dyspnea, reduced exercise capacity, exertional syncope, and premature death from right ventricular failure.
    explanation: >-
      Explicitly identifies exertional syncope as a characteristic PAH symptom.
- category: Cardiovascular
  name: Right ventricular hypertrophy
  description: Hypertrophy is the compensated right ventricular response to chronic pressure overload.
  phenotype_term:
    preferred_term: Right ventricular hypertrophy
    term:
      id: HP:0001667
      label: Right ventricular hypertrophy
  evidence:
  - reference: PMID:38716930
    reference_title: "Bone morphogenetic protein signalling in pulmonary arterial hypertension: revisiting the BMPRII connection."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pulmonary arterial hypertension (PAH) is a rare and life-threatening vascular disorder, characterised by abnormal remodelling of the pulmonary vessels and elevated pulmonary artery pressure, leading to right ventricular hypertrophy and right-sided heart failure.
    explanation: >-
      Supports right ventricular hypertrophy as a core downstream phenotype of PAH.
- category: Cardiovascular
  name: Right ventricular failure
  description: Right ventricular failure is the usual mode of death in untreated or refractory IPAH.
  phenotype_term:
    preferred_term: Right ventricular failure
    term:
      id: HP:0001708
      label: Right ventricular failure
  evidence:
  - reference: PMID:37376028
    reference_title: "Medical Management of Pulmonary Arterial Hypertension: Current Approaches and Investigational Drugs."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pulmonary arterial hypertension (PAH) is a malignant pulmonary vascular syndrome characterized by a progressive increase in pulmonary vascular resistance and pulmonary arterial pressure, which eventually leads to right heart failure and even death.
    explanation: >-
      Directly supports right heart failure as the terminal clinical consequence.
- category: Cardiovascular
  name: Peripheral edema
  description: Peripheral oedema reflects systemic venous congestion in advanced right heart failure.
  phenotype_term:
    preferred_term: Peripheral edema
    term:
      id: HP:0012398
      label: Peripheral edema
  evidence:
  - reference: PMID:40229839
    reference_title: "The prevalence of pathogenic variants in the BMPR2 gene in patients with the idiopathic pulmonary arterial hypertension in the Russian population: sequencing data and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Peripheral oedema, n (%) 52 (49.5)
      mPAP , mmHg 55.04 ± 15.928
    explanation: >-
      Reports peripheral oedema in 52 of 105 participants (49.5%) in a contemporary
      IPAH/HPAH cohort; the adjacent mPAP row preserves the source table context.
- category: Respiratory
  name: Decreased DLCO
  subtype: Lung phenotype IPAH
  description: >-
    A severely reduced diffusing capacity for carbon monoxide (<45% predicted) in the
    presence of normal or near-normal spirometry defines the IPAH lung phenotype and
    distinguishes it from classical IPAH.
  phenotype_term:
    preferred_term: Decreased DLCO
    term:
      id: HP:0045051
      label: Decreased DLCO
  evidence:
  - reference: PMID:35777416
    reference_title: "Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      patients diagnosed with IPAH and a lung phenotype defined by a DLCO of less than 45% predicted and a smoking history
    explanation: >-
      Directly defines the low-DLCO criterion for this IPAH subgroup.
histopathology:
- name: Remodeled pulmonary arterioles with immune cell accumulation
  diagnostic: true
  description: >-
    IPAH lung pathology shows eccentric and concentric intimal fibrosis with
    occlusive thickening of small pulmonary arterioles, medial hypertrophy, in-situ
    thrombosis and plexiform lesions, together with accumulation of immune cells
    around and within the remodeled arterioles. Lung biopsy is not required for and
    is generally avoided in routine diagnosis.
  finding_term:
    preferred_term: remodeled pulmonary arterioles with immune cell accumulation
  evidence:
  - reference: PMID:38797830
    reference_title: A new integrative analysis of histopathology and single cell RNA-seq reveals the CCL5 mediated T and NK cell interaction with vascular cells in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Accumulation of immune cells in remodeled pulmonary arterioles is a common finding in IPAH lung tissue
    explanation: >-
      IPAH-specific histopathological description of remodeled arterioles with immune cell
      infiltration.
genetic:
- name: BMPR2
  relationship_type: SUSCEPTIBILITY
  variant_origin: GERMLINE
  gene_term:
    preferred_term: BMPR2
    term:
      id: hgnc:1078
      label: BMPR2
  association: >-
    Rare pathogenic or likely pathogenic germline BMPR2 variants are found in a
    substantial minority of patients diagnosed with IPAH; their identification
    reclassifies the patient as heritable PAH.
  notes: >-
    Typed SUSCEPTIBILITY rather than CAUSATIVE from the perspective of this entry:
    within a population defined as idiopathic, a BMPR2 variant is an occult
    predisposing lesion whose discovery moves the patient out of this entry and into
    Heritable Pulmonary Arterial Hypertension. Penetrance is incomplete and
    sex-dependent, which is why many carriers present without any family history.
  case_fractions:
  - population: Pooled meta-analysis of 24 IPAH genetic-testing studies
    case_fraction_percent: 17.75
    cohort_size: 3124
    notes: >-
      Pooled frequency of pathogenic/likely pathogenic BMPR2 variants among patients
      carrying a clinical diagnosis of IPAH.
    evidence:
    - reference: PMID:40229839
      reference_title: "The prevalence of pathogenic variants in the BMPR2 gene in patients with the idiopathic pulmonary arterial hypertension in the Russian population: sequencing data and meta-analysis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        the frequency of P/LP variants in our cohort (10.48%) is lower than the overall average of 17.75% from the meta-analysis
      explanation: >-
        Gives the pooled BMPR2 case fraction across IPAH cohorts.
  - population: Russian IPAH cohort (whole-genome sequencing)
    case_fraction_percent: 10.48
    cohort_size: 105
    notes: Single-country contemporary IPAH cohort, not significantly different from the pooled estimate.
    evidence:
    - reference: PMID:40229839
      reference_title: "The prevalence of pathogenic variants in the BMPR2 gene in patients with the idiopathic pulmonary arterial hypertension in the Russian population: sequencing data and meta-analysis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Analysis of 105 adult IPAH patients in Russia revealed 11 patients (10.48%) as carriers of pathogenic or likely pathogenetic (P/LP) BMPR2 variants.
      explanation: >-
        Reports the BMPR2 case fraction in a whole-genome-sequenced IPAH cohort.
  evidence:
  - reference: PMID:40229839
    reference_title: "The prevalence of pathogenic variants in the BMPR2 gene in patients with the idiopathic pulmonary arterial hypertension in the Russian population: sequencing data and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Idiopathic pulmonary arterial hypertension (IPAH) is a rare and severe form of pulmonary hypertension, with a genetic basis most commonly associated with mutations in the BMPR2 gene.
    explanation: >-
      Establishes BMPR2 as the predominant genetic contributor within clinically diagnosed
      IPAH.
- name: TBX4
  relationship_type: SUSCEPTIBILITY
  variant_origin: GERMLINE
  gene_term:
    preferred_term: TBX4
    term:
      id: hgnc:11603
      label: TBX4
  association: >-
    Rare TBX4 variants are found among non-BMPR2 gene-panel-positive patients
    presenting with apparently idiopathic PAH.
  notes: >-
    TBX4 disease is enriched in childhood-onset presentations; a positive result
    reclassifies the case as heritable PAH.
  evidence:
  - reference: PMID:40229839
    reference_title: "The prevalence of pathogenic variants in the BMPR2 gene in patients with the idiopathic pulmonary arterial hypertension in the Russian population: sequencing data and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      four P/LP variants in TBX4, ATP13A3 and AQP1 genes from 27 IPAH genes in 3 patients
    explanation: >-
      Documents pathogenic TBX4 variants recovered from a clinically diagnosed IPAH cohort.
- name: ATP13A3
  relationship_type: SUSCEPTIBILITY
  variant_origin: GERMLINE
  gene_term:
    preferred_term: ATP13A3
    term:
      id: hgnc:24113
      label: ATP13A3
  association: >-
    ATP13A3 is one of the non-BMPR2 genes recurrently implicated in idiopathic and
    heritable PAH cohorts.
  evidence:
  - reference: PMID:29650961
    reference_title: Identification of rare sequence variation underlying heritable pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      rare variants in ATP13A3, AQP1 and SOX17, and provide independent validation of
    explanation: >-
      Whole-genome sequencing of an idiopathic and heritable PAH cohort identified ATP13A3
      among the newly implicated genes.
- name: SOX17
  relationship_type: SUSCEPTIBILITY
  variant_origin: GERMLINE
  gene_term:
    preferred_term: SOX17
    term:
      id: hgnc:18122
      label: SOX17
  association: >-
    SOX17 is a developmental-vascular PAH gene discovered through case-control rare
    variant burden analysis of idiopathic and heritable PAH cohorts.
  evidence:
  - reference: PMID:29650961
    reference_title: Identification of rare sequence variation underlying heritable pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      rare variants in ATP13A3, AQP1 and SOX17, and provide independent validation of
    explanation: >-
      Whole-genome sequencing of an idiopathic and heritable PAH cohort identified SOX17 among
      the newly implicated genes.
- name: GDF2
  relationship_type: SUSCEPTIBILITY
  variant_origin: GERMLINE
  gene_term:
    preferred_term: GDF2
    term:
      id: hgnc:4217
      label: GDF2
  association: >-
    GDF2 (BMP9) was independently validated as a PAH gene through rare missense
    variant burden in idiopathic and heritable PAH.
  evidence:
  - reference: PMID:29650961
    reference_title: Identification of rare sequence variation underlying heritable pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This revealed significant overrepresentation of rare variants in GDF2 after correction for multiple testing
    explanation: >-
      Supports GDF2 as a validated rare-variant PAH gene recoverable from apparently
      idiopathic cases.
environmental:
- name: Smoking history in the IPAH lung phenotype
  exposure_term:
    preferred_term: exposure to tobacco smoking
    term:
      id: ECTO:6000029
      label: exposure to tobacco smoking
  influences_mechanisms:
  - target: Unidentified Initiating Insult in a Susceptible Pulmonary Vasculature
    environmental_effect: MODULATES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Also modulating rather than predisposing, and for a reason the entry
      states itself: smoking is not a validated cause of classical disease
      here, and in this subgroup it marks a presumably smoking-related
      pulmonary vascular disease that behaves more like pulmonary hypertension
      due to lung disease. What the exposure modifies is which entity the
      patient has rather than the mechanism within it, which is the same kind
      of claim as the absence link above and is why both point at the same
      node.
    evidence:
    - reference: PMID:35777416
      reference_title: "Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "A cohort of patients meeting diagnostic criteria for IPAH with a distinct, presumably smoking-related form of pulmonary hypertension accompanied by a low DLCO, resemble patients with pulmonary hypertension due to lung disease rather than classical IPAH."
      explanation: >-
        Registry analysis identifying patients who meet the diagnostic
        criteria but have a presumably smoking-related form with low diffusing
        capacity, resembling pulmonary hypertension due to lung disease rather
        than the classical entity.
  presence: Positive
  description: >-
    A smoking history, together with a severely reduced DLCO, defines the IPAH lung
    phenotype. Smoking is not a validated cause of classical IPAH; in this subgroup
    it marks a presumably smoking-related form of pulmonary vascular disease that
    behaves more like Group 3 pulmonary hypertension.
  evidence:
  - reference: PMID:35777416
    reference_title: "Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A cohort of patients meeting diagnostic criteria for IPAH with a distinct, presumably smoking-related form of pulmonary hypertension accompanied by a low DLCO, resemble patients with pulmonary hypertension due to lung disease rather than classical IPAH.
    explanation: >-
      Directly links smoking history to the distinct low-DLCO IPAH subgroup while separating
      it from classical IPAH.
- name: Absence of a recognised drug, toxin or associated-disease exposure
  influences_mechanisms:
  - target: Unidentified Initiating Insult in a Susceptible Pulmonary Vasculature
    environmental_effect: MODULATES
    causal_link_type: DIRECT
    description: >-
      The strangest link in this backfill and worth stating plainly: this
      records a classification criterion, not a mechanism. The exposure is an
      absence, so it cannot act on anything, and the node it targets is
      described by this entry as epistemic rather than biological, holding the
      fact that no cause has been found. Absence and node are therefore the
      same statement, which is why the link is direct, and modulating is used
      because no other value in the enum is honest for something that decides
      which entity you are looking at rather than what happens inside it.
      Identifying such an exposure moves the case out of this entry entirely.
    evidence:
    - reference: DOI:10.3390/biomedicines13071773
      reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The majority of PAH cases are idiopathic; other common etiologies include connective tissue disease-associated PAH, congenital heart disease, and portopulmonary hypertension."
      explanation: >-
        Names the associated aetiologies whose absence defines the idiopathic
        designation, recording that most cases are idiopathic while connective
        tissue disease, congenital heart disease and portopulmonary
        hypertension account for others. It supplies the exclusion list rather
        than any effect.
  presence: Negative
  description: >-
    IPAH requires that recognised PAH-associated exposures - anorexigens,
    methamphetamine, dasatinib and other implicated drugs - and associated
    conditions such as connective tissue disease, congenital heart disease, HIV and
    portal hypertension be excluded. Identifying such an exposure moves the case to
    Drug- or Toxin-Induced PAH or to the relevant associated-PAH entity.
  chemicals:
  - methamphetamine
  - fenfluramine
  - dasatinib
  evidence:
  - reference: DOI:10.3390/biomedicines13071773
    reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The majority of PAH cases are idiopathic; other common etiologies include connective tissue disease-associated PAH, congenital heart disease, and portopulmonary hypertension.
    explanation: >-
      Names the associated aetiologies whose absence defines the idiopathic designation.
biochemical:
- name: N-terminal pro-B-type natriuretic peptide (NT-proBNP)
  presence: INCREASED
  biomarker_term:
    preferred_term: NT-proBNP
    term:
      id: NCIT:C88524
      label: N-Terminal Fragment Brain Natriuretic Protein
  context: >-
    Natriuretic peptide level reflects right ventricular wall stress and is one of
    the three non-invasive variables shared across validated PAH risk-stratification
    tools; it is also a standard trial endpoint. It is a severity and prognosis
    marker, not a diagnostic test for IPAH.
  evidence:
  - reference: PMID:36877098
    reference_title: Phase 3 Trial of Sotatercept for Treatment of Pulmonary Arterial Hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      change in N-terminal pro-B-type natriuretic peptide level
    explanation: >-
      NT-proBNP was a prespecified endpoint in the phase 3 PAH trial programme, supporting its
      role as a disease-activity biomarker.
diagnosis:
- name: Right heart catheterisation with exclusion of Groups 2-5 and associated PAH
  description: >-
    Diagnosis requires invasive confirmation of pre-capillary pulmonary hypertension
    (elevated mean pulmonary arterial pressure with a normal pulmonary arterial wedge
    pressure and elevated pulmonary vascular resistance), followed by systematic
    exclusion of left heart disease, lung disease/hypoxia, chronic thromboembolic
    disease and the associated and drug- or toxin-induced Group 1 subtypes. Only
    after this exclusion cascade is the case designated idiopathic.
  diagnosis_term:
    preferred_term: right heart catheterization
    term:
      id: NCIT:C80411
      label: Right Heart Catheterization
  evidence:
  - reference: DOI:10.3390/biomedicines13071773
    reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The gold standard for diagnosis remains invasive right heart catheterization.
    explanation: >-
      Establishes invasive haemodynamic confirmation as the diagnostic reference standard.
  - reference: DOI:10.3390/biomedicines13071773
    reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      without other causes of pre-capillary hypertension such as lung diseases or chronic thromboembolic pulmonary hypertension
    explanation: >-
      Supports the requirement to exclude Group 3 and Group 4 pulmonary hypertension before
      designating disease idiopathic.
- name: Transthoracic echocardiography
  description: >-
    Echocardiography is the principal noninvasive screening and probability-assessment
    study. It evaluates right-heart structure and function and possible left-heart
    causes, but does not replace confirmatory right-heart catheterisation.
  diagnosis_term:
    preferred_term: echocardiography
    term:
      id: NCIT:C16525
      label: Echocardiography Test
  evidence:
  - reference: DOI:10.3390/biomedicines13071773
    reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Along with invasive hemodynamic measurements, several noninvasive imaging
      modalities such as echocardiography and ventilation-perfusion scanning are
      key adjunct techniques.
    explanation: >-
      Establishes echocardiography as a key noninvasive adjunct in the PAH
      diagnostic pathway.
- name: Ventilation-perfusion scanning
  description: >-
    Ventilation-perfusion scanning screens for chronic thromboembolic pulmonary
    hypertension, whose exclusion is mandatory before pre-capillary pulmonary
    hypertension can be designated idiopathic Group 1 PAH.
  diagnosis_term:
    preferred_term: ventilation-perfusion scan
    term:
      id: NCIT:C38100
      label: Ventilation Perfusion Scanning
  evidence:
  - reference: DOI:10.3390/biomedicines13071773
    reference_title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Along with invasive hemodynamic measurements, several noninvasive imaging
      modalities such as echocardiography and ventilation-perfusion scanning are
      key adjunct techniques.
    explanation: >-
      Establishes ventilation-perfusion scanning as a key adjunct used to exclude
      the Group 4 chronic-thromboembolic mimic.
- name: Pulmonary function testing with DLCO
  description: >-
    Spirometry and diffusing-capacity measurement evaluate Group 3 lung disease and
    identify the low-DLCO IPAH lung phenotype. Normal or near-normal spirometry with
    severely reduced DLCO distinguishes that subtype from overt parenchymal lung
    disease.
  diagnosis_term:
    preferred_term: pulmonary function test
    term:
      id: NCIT:C38081
      label: Pulmonary Function Test
  evidence:
  - reference: PMID:35777416
    reference_title: "Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most patients with IPAH and a lung phenotype had normal or near normal
      spirometry, a severe reduction in DLCO, with the majority having no or a mild
      degree of parenchymal lung involvement on chest computed tomography.
    explanation: >-
      Defines the pulmonary-function pattern that identifies the IPAH lung
      phenotype while helping exclude overt Group 3 disease.
- name: Acute pulmonary vasodilator testing
  description: >-
    Acute vasoreactivity testing during the diagnostic right-heart catheterisation
    identifies the small subgroup of IPAH patients who may benefit from long-term
    calcium-channel blockade. This test is applied specifically in idiopathic,
    heritable and drug-associated PAH, and is one of the few points at which IPAH
    management diverges from other PAH subtypes.
  diagnosis_term:
    preferred_term: cardiac catheterization
    term:
      id: NCIT:C38044
      label: Cardiac Catheterization
  evidence:
  - reference: PMID:15939821
    reference_title: Long-term response to calcium channel blockers in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Acute pulmonary vasodilator testing with epoprostenol or nitric oxide was performed in 557 IPAH patients.
    explanation: >-
      Documents acute vasodilator testing as the standard procedure applied to IPAH patients
      to identify calcium-channel-blocker candidates.
- name: Comprehensive PAH gene panel testing
  description: >-
    Genetic testing with a curated PAH/PVOD gene panel including copy-number
    analysis is recommended for patients diagnosed with idiopathic PAH. A positive
    result reclassifies the patient as heritable PAH and enables cascade screening of
    relatives; a negative panel does not exclude genetic susceptibility.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:36302552
    reference_title: "Genetic counselling and testing in pulmonary arterial hypertension: a consensus statement on behalf of the International Consortium for Genetic Studies in PAH."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      importantly through cascade screening, the detection of healthy causal variant carriers, to whom regular assessment should be offered.
    explanation: >-
      The international consensus supports panel-based genetic testing with cascade screening
      of relatives.
  - reference: PMID:39209481
    reference_title: Genetics and precision genomics approaches to pulmonary hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Gene and variant curation by an expert panel now provides a robust framework for knowing which genes to test and how to interpret variants in clinical practice. We recommend that genetic testing be offered to specific subgroups of symptomatic patients with PAH
    explanation: >-
      Supports expert-curated gene-panel testing as current practice for symptomatic PAH
      subgroups, which include idiopathic disease.
differential_diagnoses:
- name: Heritable pulmonary arterial hypertension
  description: >-
    Clinically and mechanistically indistinguishable from IPAH at presentation; the
    distinction rests entirely on family history or on identification of a
    pathogenic germline variant. Because penetrance is incomplete and sex-dependent,
    a substantial minority of apparently idiopathic patients are genetically
    heritable.
  distinguishing_features:
  - A pathogenic or likely pathogenic germline variant in a curated PAH gene reclassifies IPAH as heritable PAH.
  - Pooled genetic testing finds pathogenic BMPR2 variants in roughly 18% of patients diagnosed as IPAH.
  - Family history may be absent in genetically heritable disease because of incomplete, age- and sex-dependent penetrance.
  disease_term:
    preferred_term: heritable pulmonary arterial hypertension
    term:
      id: MONDO:0017148
      label: heritable pulmonary arterial hypertension
  evidence:
  - reference: PMID:36302552
    reference_title: "Genetic counselling and testing in pulmonary arterial hypertension: a consensus statement on behalf of the International Consortium for Genetic Studies in PAH."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Benefits of including molecular genetic testing within the management protocol of patients with PAH include the identification of individuals misclassified by other diagnostic approaches
    explanation: >-
      Supports genetic testing as the discriminator between idiopathic and heritable PAH.
- name: Drug- or toxin-induced pulmonary arterial hypertension
  description: >-
    Group 1 PAH attributable to a culprit exposure. Exposure history is the sole
    discriminator; the downstream vascular pathology is shared.
  distinguishing_features:
  - A documented exposure to a definite PAH-associated drug or toxin (anorexigens, methamphetamine, dasatinib) excludes the idiopathic designation.
  - Some drug-induced disease is partly reversible after withdrawal of the culprit agent, which has no counterpart in IPAH.
  disease_term:
    preferred_term: drug- or toxin-induced pulmonary arterial hypertension
    term:
      id: MONDO:0017149
      label: drug- or toxin-induced pulmonary arterial hypertension
- name: Pulmonary hypertension due to lung disease or hypoxia
  description: >-
    WHO Group 3 pulmonary hypertension. The IPAH lung phenotype (low DLCO, smoking
    history) sits at the boundary: these patients satisfy IPAH haemodynamic and
    spirometric criteria but resemble Group 3 disease in age, sex distribution,
    and poor treatment response.
  distinguishing_features:
  - Group 3 disease has overt obstructive or restrictive lung disease; the IPAH lung phenotype has normal or near-normal spirometry with little parenchymal involvement on CT.
  - Response to PAH therapy is poor in both the IPAH lung phenotype and Group 3 pulmonary hypertension, and markedly better in classical IPAH.
  disease_term:
    preferred_term: pulmonary hypertension due to lung disease and/or hypoxia
    term:
      id: MONDO:0017157
      label: pulmonary hypertension owing to lung disease and/or hypoxia
  evidence:
  - reference: PMID:35777416
    reference_title: "Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Improvements in WHO functional class were observed in 54% of patients with classical IPAH, 26% of patients with IPAH with a lung phenotype, and 22% of patients with group 3 pulmonary hypertension
    explanation: >-
      Quantifies the therapeutic behaviour that places the IPAH lung phenotype closer to
      Group 3 disease than to classical IPAH.
- name: Pulmonary veno-occlusive disease and/or pulmonary capillary haemangiomatosis
  description: >-
    A venous and capillary pulmonary vasculopathy that can mimic IPAH
    haemodynamically but is managed differently and can decompensate on PAH
    vasodilators. Biallelic EIF2AK4 variants identify heritable cases.
  distinguishing_features:
  - Biallelic EIF2AK4 variants indicate PVOD/PCH rather than ordinary IPAH and materially alter management.
  - Characteristic CT findings and a very low DLCO with hypoxaemia suggest PVOD/PCH.
  disease_term:
    preferred_term: pulmonary veno-occlusive disease and/or pulmonary capillary haemangiomatosis
    term:
      id: MONDO:0018554
      label: pulmonary veno-occlusive disease and/or pulmonary capillary haemangiomatosis
  evidence:
  - reference: PMID:29650961
    reference_title: Identification of rare sequence variation underlying heritable pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Fourteen cases (1.3%) with biallelic EIF2AK4 mutations were found
    explanation: >-
      Shows that biallelic EIF2AK4 (PVOD/PCH) cases are recovered from cohorts recruited as
      idiopathic and heritable PAH, making PVOD/PCH an important differential.
treatments:
- name: Endothelin receptor antagonist therapy
  description: >-
    Ambrisentan, bosentan or macitentan block endothelin-1 signalling on the
    pulmonary vascular wall. An endothelin receptor antagonist combined with a PDE5
    inhibitor is the usual initial oral dual therapy for low- and intermediate-risk
    IPAH without major cardiopulmonary comorbidity.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: endothelin receptor antagonist
      term:
        id: NCIT:C28313
        label: Endothelin Receptor Antagonist
    - preferred_term: macitentan
      term:
        id: CHEBI:76607
        label: macitentan
    - preferred_term: ambrisentan
      term:
        id: CHEBI:135949
        label: ambrisentan
    - preferred_term: bosentan
      term:
        id: CHEBI:51450
        label: bosentan
  target_mechanisms:
  - target: Pulmonary Arterial Endothelial Dysfunction
    treatment_effect: INHIBITS
    description: >-
      Blocks the endothelin-1 arm of the endothelial vasoactive imbalance that
      initiates the remodeling cascade.
  evidence:
  - reference: DOI:10.1183/13993003.01325-2024
    reference_title: Treatment algorithm for pulmonary arterial hypertension
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Current therapies have mechanisms of action involving signallingviaone of four pathways: endothelin-1, nitric oxide, prostacyclin and bone morphogenetic protein/activin signalling.
    explanation: >-
      Establishes endothelin-1 as one of the four validated therapeutic pathways in PAH.
- name: Nitric oxide-cGMP pathway therapy
  description: >-
    Phosphodiesterase-5 inhibitors (sildenafil, tadalafil) potentiate cGMP signalling
    downstream of nitric oxide; riociguat instead stimulates soluble guanylate
    cyclase directly. Riociguat must not be combined with a PDE5 inhibitor because
    of the risk of hypotension.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: sildenafil
      term:
        id: CHEBI:9139
        label: sildenafil
    - preferred_term: tadalafil
      term:
        id: CHEBI:71940
        label: tadalafil
    - preferred_term: riociguat
      term:
        id: CHEBI:76018
        label: riociguat
  target_mechanisms:
  - target: Pulmonary Artery Smooth Muscle Cell Proliferation and Vasoconstriction
    treatment_effect: INHIBITS
    description: >-
      Augmenting cGMP signalling opposes smooth muscle vasoconstriction and
      proliferation.
  evidence:
  - reference: DOI:10.1183/13993003.01325-2024
    reference_title: Treatment algorithm for pulmonary arterial hypertension
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Current therapies have mechanisms of action involving signallingviaone of four pathways: endothelin-1, nitric oxide, prostacyclin and bone morphogenetic protein/activin signalling.
    explanation: >-
      Establishes the nitric oxide pathway as a validated therapeutic axis in PAH.
- name: Prostacyclin pathway therapy
  description: >-
    Epoprostenol, treprostinil, iloprost and the oral prostacyclin receptor agonist
    selexipag restore prostacyclin signalling. Parenteral prostacyclin, especially
    intravenous epoprostenol, is added for high-risk disease, and efficacy is greater
    with parenteral than with non-parenteral therapy.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: epoprostenol
      term:
        id: NCIT:C61748
        label: Epoprostenol
    - preferred_term: treprostinil
      term:
        id: CHEBI:50861
        label: treprostinil
    - preferred_term: selexipag
      term:
        id: CHEBI:90844
        label: selexipag
  target_mechanisms:
  - target: Pulmonary Arterial Endothelial Dysfunction
    treatment_effect: RESTORES
    description: >-
      Replaces the prostacyclin signalling lost through pulmonary endothelial
      dysfunction.
  evidence:
  - reference: DOI:10.1183/13993003.01325-2024
    reference_title: Treatment algorithm for pulmonary arterial hypertension
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Efficacy has generally been greater with therapeutic combinations and with parenteral therapy compared with monotherapy or nonparenteral therapies, and maximal medical therapy is now four-drug therapy.
    explanation: >-
      Supports escalation to parenteral prostacyclin within combination therapy for higher-risk
      PAH.
- name: Sotatercept
  description: >-
    An ActRIIA-Fc ligand trap that sequesters activin-family ligands and rebalances
    activin/BMP signalling. It is the first approved PAH therapy directed at the
    TGF-beta-superfamily imbalance underlying vascular remodeling rather than at
    vascular tone alone, and is added when low-risk status is not achieved on
    background therapy.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: targeted therapy
    term:
      id: NCIT:C93352
      label: Targeted Therapy
    therapeutic_agent:
    - preferred_term: sotatercept
      term:
        id: NCIT:C80038
        label: Sotatercept
  target_mechanisms:
  - target: Obstructive Pulmonary Vascular Remodeling
    treatment_effect: INHIBITS
    description: >-
      Rebalancing activin versus BMP signalling targets the proliferative remodeling
      process itself rather than vascular tone.
  - target: Pulmonary Arterial Endothelial Dysfunction
    treatment_effect: RESTORES
    description: >-
      Restores the balance of the BMP/activin arm of endothelial signalling that is
      depressed in PAH.
  evidence:
  - reference: PMID:38716930
    reference_title: "Bone morphogenetic protein signalling in pulmonary arterial hypertension: revisiting the BMPRII connection."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sotatercept, which contains the extracellular domain of another transforming growth factor-β family type II receptor ActRIIA fused to immunoglobin Fc domain, was recently approved by the FDA as a treatment for PAH.
    explanation: >-
      Establishes sotatercept's molecular design and approved status in PAH.
  - reference: PMID:37376028
    reference_title: "Medical Management of Pulmonary Arterial Hypertension: Current Approaches and Investigational Drugs."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Through unremitting efforts, new therapeutic drugs such as sotatercept have emerged, injecting new vitality into this field.
    explanation: >-
      Positions sotatercept as the therapeutic advance beyond the three classical vasodilator
      pathways.
- name: Calcium channel blocker therapy in acute vasoresponders
  description: >-
    High-dose amlodipine, nifedipine or diltiazem is reserved for the small IPAH
    subgroup with a positive acute vasodilator test, with close reassessment because
    only a minority of acute responders sustain long-term benefit. Empiric calcium
    channel blockade without a positive vasoreactivity test is unsafe in PAH. This
    is the clearest example of IPAH-specific, mechanism-stratified therapy.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: calcium channel blocker
      term:
        id: NCIT:C333
        label: Calcium Channel Blocker
    - preferred_term: nifedipine
      term:
        id: CHEBI:7565
        label: nifedipine
    - preferred_term: amlodipine
      term:
        id: CHEBI:2668
        label: amlodipine
    - preferred_term: diltiazem
      term:
        id: CHEBI:101278
        label: diltiazem
  target_mechanisms:
  - target: Pulmonary Artery Smooth Muscle Cell Proliferation and Vasoconstriction
    treatment_effect: INHIBITS
    description: >-
      Blocks the vasoconstrictive component of the node, which remains dominant over
      fixed remodeling in the acutely vasoreactive subgroup.
  evidence:
  - reference: PMID:15939821
    reference_title: Long-term response to calcium channel blockers in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Acute responders, defined by a fall in both mean pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR) >20%, received long-term oral CCB.
    explanation: >-
      Documents the vasoreactivity-gated indication for long-term calcium channel blockade in
      IPAH.
  - reference: PMID:15939821
    reference_title: Long-term response to calcium channel blockers in idiopathic pulmonary arterial hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      After 7.0+/-4.1 years, all but 1 long-term CCB responders were alive in NYHA class I or II, with a sustained hemodynamic improvement.
    explanation: >-
      Supports the excellent long-term outcome of the durable calcium-channel-blocker
      responder subgroup.
- name: Lung transplantation
  description: >-
    Bilateral lung or heart-lung transplantation is considered for selected patients
    with an inadequate response to maximal medical therapy.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: organ transplantation
    term:
      id: NCIT:C15289
      label: Organ Transplantation
  target_mechanisms:
  - target: Obstructive Pulmonary Vascular Remodeling
    treatment_effect: BYPASSES
    description: >-
      Replacing the remodeled pulmonary vascular bed bypasses the central effector of
      the disease.
  evidence:
  - reference: DOI:10.1183/13993003.01325-2024
    reference_title: Treatment algorithm for pulmonary arterial hypertension
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Lung transplantation remains an option for selected patients with an inadequate response to therapies.
    explanation: >-
      Supports transplantation for refractory advanced disease.
clinical_trials:
- name: NCT04576988
  phase: PHASE_III
  description: >-
    STELLAR, the randomised placebo-controlled phase 3 trial of sotatercept added to
    background PAH therapy, with 6-minute walk distance as the primary endpoint.
  target_phenotypes:
  - preferred_term: Exercise intolerance
    term:
      id: HP:0003546
      label: Exercise intolerance
  evidence:
  - reference: clinicaltrials:NCT04576988
    reference_title: A Phase 3, Randomized, Double-Blind, Placebo-Controlled Study to Compare the Efficacy and Safety of Sotatercept Versus Placebo When Added to Background Pulmonary Arterial Hypertension (PAH) Therapy for the Treatment of PAH
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The primary hypothesis of the study is that the participants receiving sotatercept will have improved 6-minute walk distance (6MWD) at 24 weeks compared to participants receiving placebo.
    explanation: >-
      ClinicalTrials.gov describes STELLAR's exercise-capacity primary endpoint.
discussions:
- discussion_id: gap_ipah_residual_etiology_after_genetic_testing
  prompt: >-
    After comprehensive gene-panel and genome sequencing has excluded known
    pathogenic variants, and all associated conditions and exposures have been ruled
    out, what actually initiates pulmonary vascular disease in the remaining
    genuinely idiopathic majority of IPAH patients?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Unidentified Initiating Insult in a Susceptible Pulmonary Vasculature
  - pathophysiology#Occult Rare Variant Burden and Reclassification to Heritable PAH
  - genetic#BMPR2
  rationale: >-
    This entry models IPAH as a diagnosis of exclusion with an explicit trigger node
    that names no trigger. Pooled genetic testing accounts for roughly one in five
    IPAH diagnoses by reclassifying them as heritable disease, which sharpens rather
    than resolves the question: the remaining four in five have no identified cause
    at all. Resolving what initiates disease in that residual population is the
    single largest mechanistic gap in this entry and determines whether IPAH remains
    a coherent disease entity or fragments into further aetiological subtypes, as
    the low-DLCO lung phenotype already suggests.
  evidence:
  - reference: PMID:40229839
    reference_title: "The prevalence of pathogenic variants in the BMPR2 gene in patients with the idiopathic pulmonary arterial hypertension in the Russian population: sequencing data and meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the frequency of P/LP variants in our cohort (10.48%) is lower than the overall average of 17.75% from the meta-analysis
    explanation: >-
      Quantifies the fraction of IPAH explained by BMPR2 genetics, and by implication the much
      larger fraction that remains unexplained.
  - reference: PMID:39209481
    reference_title: Genetics and precision genomics approaches to pulmonary hypertension.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      these cohorts are largely of European origin; greater diversity will be essential to characterise the full extent of genomic variation contributing to PH risk and treatment responses.
    explanation: >-
      Identifies ancestry bias in existing PAH genomic cohorts as a specific reason the
      residual unexplained fraction may be overestimated in non-European populations.
- discussion_id: gap_ipah_female_predominance_mechanism
  prompt: >-
    Why is IPAH roughly four times more common in women than in men, and why is this
    female predominance concentrated in the classical phenotype and largely absent in
    the low-DLCO lung phenotype?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - prevalence#Idiopathic PAH patients across epidemiological studies
  - has_subtypes#Classical IPAH
  - has_subtypes#Lung phenotype IPAH
  - pathophysiology#Unidentified Initiating Insult in a Susceptible Pulmonary Vasculature
  rationale: >-
    The entry records a 4.1:1 female-to-male incidence ratio in IPAH and shows that
    it collapses in the lung phenotype, but offers no mechanism. Sex-hormone
    metabolism, sex-differential BMP-pathway regulation and sex differences in right
    ventricular adaptation are all candidate explanations, and they make divergent
    predictions. Because the sex distribution differs so sharply between the two
    registry-defined phenotypes, resolving this would help decide whether classical
    IPAH and the lung phenotype are one disease with modifiers or two diseases
    sharing a haemodynamic definition.
  evidence:
  - reference: PMID:37461108
    reference_title: "Unraveling the epigenetic landscape of pulmonary arterial hypertension: implications for personalized medicine development."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      women have a higher incidence rate than men across multiple studies (4.3:1 in the total PAH group and 4.1:1 in the IPAH category)
    explanation: >-
      Establishes the magnitude of the female predominance the gap seeks to explain.
  - reference: PMID:35777416
    reference_title: "Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      While 99 (77%) patients in COMPERA and 133 (72%) patients in ASPIRE with classical IPAH were female, there was a lower proportion of female patients in the IPAH and a lung phenotype cohort
    explanation: >-
      Documents the phenotype-dependent collapse of the female predominance that motivates the
      question.
notes: >-
  Positioning within the dismech PAH set. This entry is deliberately scoped to what
  is distinctive about idiopathic disease and defers the shared cascade to the
  pulmonary_vascular_remodeling module: five pathophysiology nodes declare
  conforms_to against that module (endothelial dysfunction, PASMC
  proliferation/vasoconstriction, obstructive remodeling, increased PVR, and the
  PAH/right-ventricular consequence) rather than re-deriving the mechanism. The
  IPAH-specific content is concentrated in (1) the "Unidentified Initiating Insult"
  trigger node, which substitutes for the germline BMPR2 lesion of
  Heritable_Pulmonary_Arterial_Hypertension and the culprit exposure of
  Drug_or_Toxin-Induced_Pulmonary_Arterial_Hypertension; (2) the "Occult Rare
  Variant Burden" node, which models the porous IPAH/HPAH boundary quantitatively
  (pooled 17.75% pathogenic BMPR2 across 3124 IPAH patients) rather than as prose;
  (3) the three registry- and physiology-defined subtypes (classical, low-DLCO lung
  phenotype, vasoresponder); (4) female predominance; and (5) the IPAH-specific
  CCL5 T/NK immune-vascular crosstalk node. Genes are typed SUSCEPTIBILITY rather
  than CAUSATIVE on purpose: from the perspective of a population defined as
  idiopathic, discovering such a variant moves the patient out of this entry.

  Deliberate omissions. The 2022 ESC/ERS guideline (PMID:36017548) has no PubMed
  abstract, so the current numeric haemodynamic thresholds (mPAP above 20 mmHg,
  PAWP at or below 15 mmHg, PVR above 2 Wood units) that the deep-research report
  supplied are described qualitatively rather than asserted with a fabricated
  quote; the qualitative pre-capillary definition is instead evidenced from a
  cached review. Incidence (2.5-7.5 per million/year), diagnostic delay (about 2.8
  years to diagnosis), and contemporary survival percentages appeared in the
  deep-research report but were sourced from full-text pages not present in the
  cached references, so they are not asserted here. The 2024 World Symposium
  12-definitive-gene list was reported by deep research from full text; only the
  individual genes independently verifiable from cached references (BMPR2, TBX4,
  ATP13A3, SOX17, GDF2) are curated. The ferroptosis mechanism is recorded as an
  EMERGING mechanistic_hypotheses entry rather than a pathophysiology node because
  the therapeutic evidence is preclinical and the finding is PAH-wide rather than
  IPAH-specific.
references:
- reference: PMID:15939821
  title: Long-term response to calcium channel blockers in idiopathic pulmonary arterial hypertension.
  findings: []
- reference: PMID:29540357
  title: "Pulmonary arterial hypertension: pathogenesis and clinical management."
  findings: []
- reference: PMID:29650961
  title: Identification of rare sequence variation underlying heritable pulmonary arterial hypertension.
  findings: []
- reference: PMID:35777416
  title: "Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis."
  findings: []
- reference: PMID:36302552
  title: "Genetic counselling and testing in pulmonary arterial hypertension: a consensus statement on behalf of the International Consortium for Genetic Studies in PAH."
  findings: []
- reference: PMID:36603064
  title: BMPR2 Mutation and Metabolic Reprogramming in Pulmonary Arterial Hypertension.
  findings: []
- reference: PMID:36877098
  title: Phase 3 Trial of Sotatercept for Treatment of Pulmonary Arterial Hypertension.
  findings: []
- reference: PMID:37376028
  title: "Medical Management of Pulmonary Arterial Hypertension: Current Approaches and Investigational Drugs."
  findings: []
- reference: PMID:37461108
  title: "Unraveling the epigenetic landscape of pulmonary arterial hypertension: implications for personalized medicine development."
  findings: []
- reference: PMID:38716930
  title: "Bone morphogenetic protein signalling in pulmonary arterial hypertension: revisiting the BMPRII connection."
  findings: []
- reference: PMID:38797830
  title: A new integrative analysis of histopathology and single cell RNA-seq reveals the CCL5 mediated T and NK cell interaction with vascular cells in idiopathic pulmonary arterial hypertension.
  findings: []
- reference: PMID:39209481
  title: Genetics and precision genomics approaches to pulmonary hypertension.
  findings: []
- reference: PMID:39421926
  title: Ferroptosis-Mediated Inflammation Promotes Pulmonary Hypertension.
  findings: []
- reference: PMID:40229839
  title: "The prevalence of pathogenic variants in the BMPR2 gene in patients with the idiopathic pulmonary arterial hypertension in the Russian population: sequencing data and meta-analysis."
  findings: []
- reference: DOI:10.1183/13993003.01325-2024
  title: Treatment algorithm for pulmonary arterial hypertension
  findings: []
- reference: DOI:10.3390/biomedicines13071773
  title: "State of the Art in Pulmonary Arterial Hypertension: Molecular Basis, Imaging Modalities, and Right Heart Failure Treatment"
  findings: []
- reference: clinicaltrials:NCT04576988
  title: A Phase 3, Randomized, Double-Blind, Placebo-Controlled Study to Compare the Efficacy and Safety of Sotatercept Versus Placebo When Added to Background Pulmonary Arterial Hypertension (PAH) Therapy for the Treatment of PAH
  findings: []

📚

References & Deep Research