Génétique de l’hypertension artérielle pulmonaire: données récentes et applications pratiques

The genetics of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease for which there is an ever-expanding body of genetic and related pathophysiological information on disease pathogenesis. Many germline gene mutations have now been described, including mutations in the gene coding bone morphogenic protein receptor type 2 (BMPR2) and related genes. Recent advanced gene-sequencing methods have facilitated the discovery of additional genes with mutations among those with and those without familial forms of PAH (CAV1, KCNK3, EIF2AK4). The reduced penetrance, variable expressivity, and female predominance of PAH suggest that genetic, genomic, and other factors modify disease expression. These multi-faceted variations are an active area of investigation in the field, including but not limited to common genetic variants and epigenetic processes, and may provide novel opportunities for pharmacological intervention in the near future. They also highlight the need for a systems-oriented multi-level approach to incorporate the multitude of biological variations now associated with PAH. Ultimately, an in-depth understanding of the genetic factors relevant to PAH provides the opportunity for improved patient and family counseling about this devastating disease.

Heritable forms of pulmonary arterial hypertension

Tremendous progress has been made in understanding the genetics of heritable pulmonary arterial hypertension (HPAH) since its description in the 1950s. Germline mutations in the gene coding bone morphogenetic receptor type 2 (BMPR2) are detectable in the majority of cases of HPAH, and in a small proportion of cases of idiopathic pulmonary arterial hypertension (IPAH). Recent advancements in gene sequencing methods have facilitated the discovery of additional genes with mutations among those with and without familial PAH (CAV1, KCNK3). HPAH is an autosomal dominant disease characterized by reduced penetrance, variable expressivity, and female predominance. These characteristics suggest that genetic and nongenetic factors modify disease expression, highlighting areas of active investigation. The reduced penetrance makes genetic counseling complex, as the majority of carriers of PAH-related mutations will never be diagnosed with the disease. This issue is increasingly important, as clinical testing for BMPR2 and other mutations is now available for the evaluation of patients and their at-risk kin. The possibilities to avoid mutation transmission, such as the rapidly advancing field of preimplantation genetic testing, highlight the need for all clinicians to understand the genetic features of PAH risk.

Genetics of pulmonary arterial hypertension

Tremendous progress has been made in understanding the genetics of hereditable pulmonary arterial hypertension (HPAH) since its description in the 1950s. Germline mutations in the gene coding bone morphogenetic receptor type 2 ( BMPR2) are detectable in the majority of cases of HPAH, and in a small proportion of cases of idiopathic pulmonary arterial hypertension (IPAH). HPAH is an autosomal dominant disease characterized by reduced penetrance, variable expressivity, female predominance, and genetic anticipation. These characteristics suggest that endogenous and exogenous factors modify disease expression and areas of emphasis for future investigation. The variable clinical expression makes genetic counseling complex because the majority of carriers of a BMPR2 mutation will not be diagnosed with the disease. This issue will become increasingly important, as clinical testing for BMPR2 mutations is now available for the evaluation of patients and family members with HPAH and IPAH.

Hypertension pulmonaire postembolique

INTRODUCTION

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare disease characterized by the persistence of thromboemboli obstructing the pulmonary arteries as an organized tissue. The consequence is an increase in pulmonary vascular resistance resulting in pulmonary hypertension (PH) and progressive right heart failure.

BACKGROUND

It is difficult to recognize the postembolic nature of PH because there is no known history of thromboembolic disease in more than 50% of cases. Diagnosis is based on the presence of mismatched segmental defects in the ventilation-perfusion scanning. When CTEPH is suspected, pulmonary angiography and high-resolution CT scan are required to establish the diagnosis and to assess the operability. Pulmonary angiography is always performed in conjunction with a diagnostic right heart catheterization, which is required to confirm the diagnosis of PH and to determine the degree of hemodynamic impairement. If there is a good correlation between the pulmonary vascular resistance and the anatomical obstruction, pulmonary endarterectomy (PEA) must be proposed. Otherwise, vasodilator and antiproliferative treatments and lung transplantation represent interesting alternatives.

VIEWPOINT AND CONCLUSION

PEA remains the treatment of choice for eligible patients. Nevertheless, there is a need to conduct randomized trials to assess the efficacy of novel medical therapies in some situations: (1) in inoperable CTEPH due to distal lesions, (2) before PEA (therapeutic bridge) in patients who are considered "high risk" due to extremely poor hemodynamics, (3) in patients with persistent pulmonary hypertension after surgery.

Hypertension artérielle pulmonaire primitive familiale révélée par l’association bilatérale chémosis, myopisation et exophtalmie

PURPOSE

To report a rare case of primary pulmonary hypertension (PPH) revealed by a relapsing chemosis, exophthalmos, and subacute myopia.

PATIENTS AND METHODS

A 46-year-old woman presented with recurrent bouts of chemosis, exophthalmos, and subacute myopia. Her visual troubles were triggered by physical effort. She had a history of a longstanding high blood pressure that was noncompliant to all conventional hypotensive therapy. Automated refraction under cycloplegia showed recent myopia. At observation she had a bilateral, moderate chemosis. Hertel exophthalmometer measured a symmetric exophthalmos of 23 mm. Intraocular pressure was 20 mmHg OD and 24 mmHg OS. Eye fundus was strictly normal.

RESULTS

Laboratory analysis showed no thyroid or inflammatory disease. HIV serology was negative as were antinuclear antibodies. Orbital CT confirmed the axial, symmetric exophthalmos. Echocardiogram brought out the diagnosis of PPH. Genetic studies by PCR localized the BMPR2 mutation that is characteristic of the familial type of PPH. Symptoms decreased under treatment.

DISCUSSION

PPH is a rare disease caused by thickening of the arteriolar walls in the pulmonary bed, which results in a right-heart hypertension with venous stasis. Many authors have reported different posterior segment diseases secondary to PPH. However, anterior segment manifestations are extremely rare. These may be caused by a ciliary body congestion and retrobulbar vasodilatation.

CONCLUSION

The association of chemosis, exophthalmos, and subacute myopia is unusual in PPH. We recommend keeping in mind the PPH as a differential diagnosis in those cases, especially in patients who suffer from high blood pressure.

Genes and Pulmonary Arterial Hypertension

Familial pulmonary arterial hypertension (FPAH) was first described more than 50 years ago. Before the availability of modern genetic tools, studies of the genealogies demonstrated that these cases segregated as an autosomic dominant trait, with an incomplete penetrance and a genetic anticipation phenomenon by which age at onset of the disease is decreasing in the subsequent generations. Germline mutations in the gene coding for the bone morphogenetic protein receptor II (BMPR2) are present in more than 70% of FPAH and up to 26% of idiopathic, apparently sporadic cases (IPAH). Incomplete penetrance (around 20%) is a major pitfall because FPAH becomes ignored when the disease skips one or several generations. Genetic counseling is complex, with a significant number of BMPR2 mutation healthy carriers screened in some families. Incomplete penetrance puts them in the anxious situation of being potentially affected in the future by this devastating condition or to transmit this risk to their offspring. Nevertheless, genetic testing and counseling is about to become a standard in the management of PAH. Recent international guidelines on PAH state that genetic testing is recommended in FPAH and that IPAH patients have to be informed about the availability of such testing.