Chronic thromboembolic pulmonary hypertension (CTEPH) is an important cause of pulmonary hypertension that is commonly considered to be the consequence of acute pulmonary embolic disease [1]. Following an acute event, unresolved residual thrombus becomes organized and fibrosed, leading to ongoing obstruction to pulmonary blood flow and progressive pulmonary hypertension, right ventricular dysfunction, and death [2].

Heterozygous germline mutations of BMPR2 are the most important predisposing factors for heritable pulmonary arterial hypertension (HPAH). BMPR2 mutation was occasionally reported in pulmonary veno-occlusive disease (PVOD) [3], appetite suppressant-related PAH [4], and PAH with congenital heart disease [5]. In this study we identified a missense mutation (c.2296A > G) located in BMPR2 exon 12 in a patient with CTEPH. This is the first report of a BMPR2 mutation in CTEPH. The genetic predisposing factor is an important component in the process of this CTEPH patient.

Case Report

A 29-year-old female complained of progressive shortness of breath and chest tightness on exertion over 6 years. Past medical history consisted of an acute pulmonary embolism 6 years prior and an appendectomy. Physical examination revealed elevated jugular venous pressure, wet rale from the bottom of the left lung, a prominent second heart sound, and grade 3/6 systolic murmur in the tricuspid area. Serology for collagen vascular disease was negative. A chest radiograph showed the right atrium and ventricular enlargement and dilated main pulmonary arteries. The cardiothoracic ratio was 0.67 (Fig. 1). Lung perfusion scanning revealed multiple, bilateral perfusion defects of the blood with only about 34.65 % perfusion in the left lung. Right heart catheterization demonstrated a mean pulmonary arterial pressure of 46 mmHg, mean pulmonary capillary wedge pressure of 9 mmHg, cardiac output of 3.08 L/min, pulmonary vascular resistance of 12.01 Wood units, and the negative response to the acute vasodilator drug testing after inhaling iloprost. Pulmonary angiography revealed multiple stenoses from the beginning of the bilateral segment, and subsegmental arteries scattered perfusion defects in peripheral vessels (Fig. 2). After undergoing a series of examinations, the patient was diagnosed with CTEPH and was treated with sildenafil and beraprost to reduce the pulmonary hypertension and with warfarin for anticoagulation. Unfortunately, the patient died of right heart failure 3 years later.

Fig. 1
figure 1

Chest X-ray of patient shows the enlarged right atrium and ventricular and dilated main pulmonary arteries. Cardiothoracic ratio was 0.67

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Fig. 2
figure 2

Pulmonary angiographies of the patient in different positions reveal multiple stenoses from the beginning of the bilateral segment and subsegmental arteries (arrows) scattered perfusion defects in peripheral vessels

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Molecular Methods

The patient gave her written informed consent for genetic analyses prior to participation. The study was approved by the Ethics Committee of Shanghai Pulmonary Hospital (k10–036). Direct screening using an ABI 3730 (Applied Biosystems, Foster City, CA, USA) was adopted to detect the point mutations in the coding regions and intron/exon boundaries of BMPR2. Genomic DNA was isolated from peripheral blood leukocytes. Fifteen pairs of PCR primers were designed to amplify 13 exons and the 5′, 3′ untranslated region of the BMPR2 gene [6]. The results were compared with the reference sequence of the BMPR2 gene (accession No. NM-001204.5) using the ABI SeqScape software ver. 2.5 (Applied Biosystems). The mutation nomenclature followed current guidelines as recommended by the Human Genome Variation Society (http://www.hgvs.org/mutnomen/). The mutation numbering employed in this report is based on the cDNA sequence, where +1 designates the A of the ATG initiation codon (Fig. 3).

Fig. 3
figure 3

Sequencing analysis of PCR product indicated a variation (A → T change) at codon 766 in exon 12 of the BMPR2 gene in the patient

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Discussion

Although a number of BMPR2 mutations have been reported in a variety of diseases, mutation in CTEPH has not been previously studied. Our study provides innovative insight into etiology of CTEPH. The early onset and fast progress of CTEPH in this patient indicates the damaging effect of this variant.

The patient in our study had an acute pulmonary embolism 6 years before diagnosis of CTEPH. Her BMPR2 mutation may be a genetic risk factor in triggering the onset of the disease. The patient’s age at diagnosis was 29 years old, about 20 years younger than the average age of the patients in Pengo’s study [7], and she died 3 years after CTEPH confirmation. BMPR2 mutation may play an important role in the early onset of the disease and accelerated her pulmonary artery occlusion.

BMPR2 encodes the protein BMPR II, a member of the transforming growth factor-β (TGF-β) cell signaling superfamily, which is a constitutively active serine/threonine receptor kinase whose downstream signaling has profound effects on developmental processes, including vasculogenesis [8]. Mutations of BMPR2 result in downregulation Smad signaling in pulmonary arterial smooth muscle cells, with resultant loss of the antiproliferative effect. The imbalance of proproliferative and antiapoptotic effects promotes the development of PAH [9]. Exon 12 is the largest exon of the gene and forms part of the intracytoplasmic tail domain which is important for interactions of BMPR-II with β-actin. It has been previously demonstrated that a missense mutation or a truncated mutation in exon 12 decreases activity to phosphorylate the protein cofilin and inhibits the interaction with downstream mediators of BMPR-II signaling, e.g., Smad1 and P38MAPK [9, 10]. In this patient, unresolved thrombus combined with BMPR2 mutation may contribute to the elevated pulmonary vascular resistance and accelerated the progress of the disease.

Although our study is the first report that identifies the BMPR2 mutation in CTEPH, a larger number of patients is needed to access the mutation rate and to define the role of the BMPR2 mutation in the pathogenesis of CTEPH.