Familial pulmonary hypertension in association with an abnormal hemoglobin. Insights into the pathogenesis of primary pulmonary hypertension

High levels of zinc-protoporphyrin identify iron metabolic abnormalities in pulmonary arterial hypertension

Iron homeostasis influences the development of pulmonary arterial hypertension (PAH) associated with hypoxia or hematologic disorders. To investigate whether severity of idiopathic PAH (IPAH) is impacted by alterations in iron metabolism, we assessed iron metabolic markers, including levels of zinc-protoporphyrin (Zn-pp), transferrin receptor, and red blood cell numbers and morphology in IPAH, associated PAH and sleep apnea-induced pulmonary hypertension patients in comparison to healthy controls and asthmatics. Despite similarly normal measures of iron metabolism, Zn-pp levels in IPAH and sleep apnea patients were elevated approximately twofold, indicating deficient iron incorporation to form heme and levels were closely related to measures of disease severity. Consistent with high Zn-pp, PAH patients had increased red cell distribution width (RDW). In an expanded cohort including patients with IPAH and familial disease, the RDW was validated and related to clinical parameters of severity; including pulmonary artery pressures and 6-minute walk distances. These results reveal an increased prevalence of subclinical functional iron deficiency in primary forms of PAH that is quantitatively related to disease severity. This suggests that altered iron homeostasis influences disease progression and demonstrates the importance of closely monitoring iron status in PAH patients.

Vascular complications after splenectomy for hematologic disorders

The most widely recognized long-term risk of splenectomy is overwhelming bacterial infection. More recently, thrombosis has become appreciated as another potential complication of the procedure. Because of these long-term risks, the indications for and timing of splenectomy are debated in the medical community. Accordingly, the adverse effects and benefits of splenectomy for hematologic disorders and other conditions demand further study. This comprehensive review summarizes the existing literature pertaining to vascular complications after splenectomy for hematologic conditions and attempts to define the potential pathophysiologic mechanisms involved. This complex topic encompasses diverse underlying conditions for which splenectomy is performed, diverse thrombotic complications, and multiple pathophysiologic mechanisms.

Delayed adverse vascular events after splenectomy in hereditary spherocytosis

BACKGROUND

It is probable that the variety and frequency of delayed adverse vascular events after splenectomy are underappreciated. Splenectomy is performed for a wide variety of conditions, and delayed postsplenectomy hazards are not often studied.

OBJECTIVE

To estimate the relative risk of adverse vascular events in members of hereditary spherocytosis families who have or have not had a splenectomy.

METHODS

Members of families in which hereditary spherocytosis exists were systematically questioned about adverse vascular events.

RESULTS

The cumulative incidence of arterial and venous events at age 70 years was greater in persons who had undergone a splenectomy for spherocytosis (arterial, 22% females, 32% males; venous, 20% females, 19% males) than in affected persons who did not undergo splenectomy (arterial, 3% females, 2% males; venous, 6% females, 4% males) or non-affected family members (arterial, 10% females, 17% males; venous, 4% females, 12% males). Affected subjects who undergo splenectomy are at greatly increased risk of arterial events as compared to affected subjects who do not undergo splenectomy [arterial, hazard ratio (HR) 7.2, 95% confidence interval (CI) 2.8-17.2; venous, HR 3.3, 95% CI 1.1-9.8].

CONCLUSION

There is a significant, long-lasting, increased risk of adverse arterial and venous thromboembolic events after splenectomy performed for hereditary spherocytosis. A review of the literature indicates that this is also true when splenectomy is performed for several other indications.

Classification and epidemiology of pulmonary hypertension

Pulmonary hypertension is a complex disease that can be idiopathic, familial, or associated with a wide range of disease processes. This article outlines the classification of primary pulmonary hypertension and discusses the various types of the disease.

Primary pulmonary hypertension

Primary pulmonary hypertension (PPH) is a rare disorder characterised by raised pulmonary-artery pressure in the absence of secondary causes. Precapillary pulmonary arteries are affected by medial hypertrophy, intimal fibrosis, microthrombosis, and plexiform lesions. Most individuals present with dyspnoea or evidence of right heart failure. Echocardiography is the best non-invasive test to screen for suspected pulmonary hypertension. The discovery of mutations in the coding region of the gene for bone morphogenetic protein receptor 2 in patients with familial and sporadic PPH may help not only to elucidate pathogenesis but also to direct future treatment options. The pathogenesis is not completely understood, but recent investigations have revealed many possible candidate modifier genes. Without treatment, the disorder progresses in most cases to right heart failure and death. With current therapies such as epoprostenol, progression of disease is slowed, but not halted. Many promising new therapeutic options, including prostacyclin analogues, endothelin-1-receptor antagonists, and phosphodiesterase inhibitors, improve clinical function and haemodynamic measures and may prolong survival.

Genetic aspects of pulmonary arterial hypertension

This paper concentrates on the genetic aspects of pulmonary arterial hypertension (PAH), a diagnostically based subclass of pulmonary hypertension that includes primary pulmonary hypertension (PPH). During the past year, patients with familial and sporadic PPH were found to have germline heterozygous missense, nonsense and frameshift mutations in bone morphogenetic protein receptor II (BMPR2). Mutations in BMPR2, a member of the transforming growth factor-beta (TGF-beta) receptor superfamily, are predicted to interrupt the bone morphogenetic protein (BMP) signalling pathway, resulting in proliferation, rather than apoptosis of cells within small arterioles. Mechanistically, haploinsufficiency was found by using in vitro gene expression experiments, but a dominant-negative mechanism has not been excluded. The failure to find BMPR2 mutations in all families with familial PPH and in all patients with sporadic PPH suggests that other genes remain to be identified. Mutations in ALK1, a TGF-beta type 1 receptor, previously known to cause type 2 hereditary haemorrhagic telangiectasia (HHT), have also been reported in a few HHT families with clinical and histological features of PPH. The clinical development of PPH, as in neoplasia, appears to require 'two hits' The two hits can be provided either by genetic or environmental factors.

Genetics of primary pulmonary hypertension

Familial primary pulmonary hypertension (FPPH) is a well described clinical entity in which the disease occurs in at least two first degree relatives. It is clinically and pathologically indistinguishable from sporadic PPH. Mutations in the gene which encodes bone morphogenetic receptor 2 have recently been discovered in familial and sporadic PPH. This review discusses the basic clinical and genetic features of FPPH, and describes the research that led to the discovery of the disease-causing gene. Potential mechanisms of disease are also discussed, as well as implications for future investigations.

Genetics and immunogenetic aspects of primary pulmonary hypertension

Primary pulmonary hypertension (PPH), also referred to as unexplained or idiopathic pulmonary hypertension, is the clinical term used to describe a condition in patients for which we can find no underlying cause. Patients with PPH not uncommonly also have evidence of immune dysregulation: autoimmune disorders, drug therapy, or HIV infections. We will review these associations and possible relevant abnormalities in immune regulation with regard to how they may play a role in the pathogenesis of PPH. Autoantibody-HLA correlations have been observed in several subsets of PPH patients. In addition, a familial form of PPH has been described and characterized with linkage to chromosome 2q31-q32. The identification of a specific gene for PPH and the subsequent understanding of its effects will help us identify the basic cause of PPH. Furthering our understanding regarding the role(s) and significance of immunogenetic as well as genetic aspects of the pathogenesis and pathophysiology of PPH should also lead to improved therapeutic modalities for PPH.

Mapping of familial primary pulmonary hypertension locus (PPH1) to chromosome 2q31-q32

BACKGROUND

The pathogenesis of primary pulmonary hypertension (PPH) is unknown, although in some instances families with multiple affected members suggest a genetic etiology.

METHODS AND RESULTS

We used microsatellite markers and linkage analysis in a large family with PPH to determine the chromosomal location of their disease gene. We tested a second, ethnically distinct, family for cosegregation of disease with markers from the linked region. We mapped the disease locus PPH1; GDB/HUGO designation (GDB:1381541; July 1996), approved when this work was accepted for publication in abstract form (Circulation. 1996;94[suppl I]:1-49.), in these families to a 27-cM region on chromosome 2q31-q32, with a maximum lod score of 3.87 associated with markers D2S350 and D2S364.

CONCLUSIONS

Cosegregation of this region with disease in different ethnic groups suggests that we mapped an important locus in familial PPH. Careful study of additional families and sporadic cases will be required to confirm this localization of PPH1 and characterize its overall role.

Familial association of primary pulmonary hypertension and a new low-oxygen affinity beta-chain hemoglobinopathy, Hb Washtenaw

A Hungarian-American kindred with familial primary pulmonary hypertension (PPH) and a new, low-oxygen affinity beta-chain variant hemoglobin, Hb Washtenaw, is described. The index case presented with severe PPH and was found to have the abnormal hemoglobin. Two siblings with the abnormal hemoglobin also demonstrated increased pulmonary artery pressures on exercise echocardiography suggestive of early PPH. The occurrence of PPH and the abnormal hemoglobin could be due to genetic or biochemical factors or simply coincidental. A previous study had described a possible association of an abnormal beta-chain variant hemoglobin, Hb Warsaw, and PPH. It was suggested that the putative gene for familial PPH may be located near the beta-globin gene on chromosome 11. The association of PPH and the beta-chain variant hemoglobin in this kindred adds further support to this hypothesis.

Hb Washtenaw [ beta 11(A8)Val-->Phe]: an electrophorectically silent, unstable, low oxygen affinity variant associated with anemia and chronic cyanosis

Hb Washtenaw [beta 11(A8)Val-->Phe] is a new, low oxygen affinity variant with a previously undescribed substitution, identified in seven members over three generations of a Hungarian-American family. The hemoglobin is mildly unstable and the family members studied are clinically asymptomatic but mildly cyanotic, and some exhibit mild anemia. The index case had severe pulmonary hypertension and some of the family members had increased pulmonary vascular resistance on echocardiography. An association between the inheritance of this abnormal hemoglobin and the pathogenesis of primary pulmonary hypertension is suggested but the mechanism is unclear.