Pulmonary Vascular Complications in Hereditary Hemorrhagic Telangiectasia and the Underlying Pathophysiology.

In this review, we discuss the role of transforming growth factor-beta (TGF-ß) in the development of pulmonary vascular disease (PVD), both pulmonary arteriovenous malformations (AVM) and pulmonary hypertension (PH), in hereditary hemorrhagic telangiectasia (HHT). HHT or Rendu-Osler-Weber disease is an autosomal dominant genetic disorder with an estimated prevalence of 1 in 5000 persons and characterized by epistaxis, telangiectasia and AVMs in more than 80% of cases, HHT is caused by a mutation in the ENG gene on chromosome 9 encoding for the protein endoglin or activin receptor-like kinase 1 (ACVRL1) gene on chromosome 12 encoding for the protein ALK-1, resulting in HHT type 1 or HHT type 2, respectively. A third disease-causing mutation has been found in the SMAD-4 gene, causing a combination of HHT and juvenile polyposis coli. All three genes play a role in the TGF-ß signaling pathway that is essential in angiogenesis where it plays a pivotal role in neoangiogenesis, vessel maturation and stabilization. PH is characterized by elevated mean pulmonary arterial pressure caused by a variety of different underlying pathologies. HHT carries an additional increased risk of PH because of high cardiac output as a result of anemia and shunting through hepatic AVMs, or development of pulmonary arterial hypertension due to interference of the TGF-ß pathway. HHT in combination with PH is associated with a worse prognosis due to right-sided cardiac failure. The treatment of PVD in HHT includes medical or interventional therapy.

Prevalence and diagnostic value of nail fold capillary microscopy in hereditary hemorrhagic telangiectasia: A retrospective study.

Abnormal vasculature is a key feature of hereditary hemorrhagic telangiectasia (HHT) and can also present in the nail fold capillary beds. However, the exact prevalence and the clinical diagnostic value in HHT are still largely unknown. The nail fold can be easily and noninvasively inspected with a capillary microscope. We therefore retrospectively assessed the prevalence and diagnostic value of abnormal nail fold capillaries in all patients who were screened between January 2000 and July 2017 for the presence of HHT and underwent capillary microscopy in St Antonius Hospital, The Netherlands. Capillary microscopy results and clinical characteristics were extracted from medical files and the prevalence of abnormal nail fold capillaries was calculated and the diagnostic value of the Curaçao criteria with and without capillary microscopy results was assessed. Of the 1761 individuals screened, 923 (52%) were diagnosed with a clinical and/or genetic HHT diagnosis. In these patients, capillary microscopy was normal in 23% (n = 218), enlarged loops were seen in 11% (n = 99), and giant loops in 66% (n = 606). The sensitivity and specificity of the Curaçao criteria for the diagnosis of HHT without capillary microscopy results were 96% and 90%, respectively. The addition of the presence of giant loops to the Curaçao criteria led to a small increase in sensitivity to 97% without affecting the specificity. In conclusion, the prevalence of nail fold abnormalities in patients with HHT is high. Capillary microscopy can be a useful, easy, and noninvasive diagnostic tool in HHT.

Decreased Expression of Vascular Endothelial Growth Factor Receptor 1 Contributes to the Pathogenesis of Hereditary Hemorrhagic Telangiectasia Type 2.

BACKGROUND: Hereditary Hemorrhagic Telangiectasia type 2 (HHT2) is an inherited genetic disorder characterized by vascular malformations and hemorrhage. HHT2 results from ACVRL1 haploinsufficiency, the remaining wild-type allele being unable to contribute sufficient protein to sustain endothelial cell function. Blood vessels function normally but are prone to respond to angiogenic stimuli, leading to the development of telangiectasic lesions that can bleed. How ACVRL1 haploinsufficiency leads to pathological angiogenesis is unknown. METHODS: We took advantage of Acvrl1+/- mutant mice that exhibit HHT2 vascular lesions and focused on the neonatal retina and the airway system after Mycoplasma pulmonis infection, as physiological and pathological models of angiogenesis, respectively. We elucidated underlying disease mechanisms in vitro by generating Acvrl1+/- mouse embryonic stem cell lines that underwent sprouting angiogenesis and performed genetic complementation experiments. Finally, HHT2 plasma samples and skin biopsies were analyzed to determine whether the mechanisms evident in mice are conserved in humans. RESULTS: Acvrl1+/- retinas at postnatal day 7 showed excessive angiogenesis and numerous endothelial "tip cells" at the vascular front that displayed migratory defects. Vascular endothelial growth factor receptor 1 (VEGFR1; Flt-1) levels were reduced in Acvrl1+/- mice and HHT2 patients, suggesting similar mechanisms in humans. In sprouting angiogenesis, VEGFR1 is expressed in stalk cells to inhibit VEGFR2 (Flk-1, KDR) signaling and thus limit tip cell formation. Soluble VEGFR1 (sVEGFR1) is also secreted, creating a VEGF gradient that promotes orientated sprout migration. Acvrl1+/- embryonic stem cell lines recapitulated the vascular anomalies in Acvrl1+/- (HHT2) mice. Genetic insertion of either the membrane or soluble form of VEGFR1 into the ROSA26 locus of Acvrl1+/- embryonic stem cell lines prevented the vascular anomalies, suggesting that high VEGFR2 activity in Acvrl1+/- endothelial cells induces HHT2 vascular anomalies. To confirm our hypothesis, Acvrl1+/- mice were infected by Mycoplasma pulmonis to induce sustained airway inflammation. Infected Acvrl1+/- tracheas showed excessive angiogenesis with the formation of multiple telangiectases, vascular defects that were prevented by VEGFR2 blocking antibodies. CONCLUSIONS: Our findings demonstrate a key role of VEGFR1 in HHT2 pathogenesis and provide mechanisms explaining why HHT2 blood vessels respond abnormally to angiogenic signals. This supports the case for using anti-VEGF therapy in HHT2.

Executive summary of the 12th HHT international scientific conference.

Hereditary hemorrhagic telangiectasia is an autosomal dominant trait affecting approximately 1 in 5000 people. A pathogenic DNA sequence variant in the ENG, ACVRL1 or SMAD4 genes, can be found in the majority of patients. The 12th International Scientific HHT Conference was held on June 8-11, 2017 in Dubrovnik, Croatia to present and discuss the latest scientific achievements, and was attended by over 200 scientific and clinical researchers. In total 174 abstracts were accepted of which 58 were selected for oral presentations. This article covers the basic science and clinical talks, and discussions from three theme-based workshops. We focus on significant emergent themes and unanswered questions. Understanding these topics and answering these questions will help to define the future of HHT research and therapeutics, and ultimately bring us closer to a cure.

Pulmonary Arterial Hypertension and Hereditary Haemorrhagic Telangiectasia.

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant inherited disease characterised by multisystemic vascular dysplasia. Heritable pulmonary arterial hypertension (HPAH) is a rare but severe complication of HHT. Both diseases can be the result of genetic mutations in ACVLR1 and ENG encoding for proteins involved in the transforming growth factor-beta (TGF-ß) superfamily, a signalling pathway that is essential for angiogenesis. Changes within this pathway can lead to both the proliferative vasculopathy of HPAH and arteriovenous malformations seen in HHT. Clinical signs of the disease combination may not be specific but early diagnosis is important for appropriate treatment. This review describes the molecular mechanism and management of HPAH and HHT.

The use of echo density to quantify pulmonary right-to-left shunt in transthoracic contrast echocardiography.

AIMS: Transthoracic contrast echocardiography (TTCE) is the recommended screening tool to detect pulmonary right-to-left shunt (RLS) caused by pulmonary arteriovenous malformations (PAVMs). We assessed a novel method to quantify the RLS using the change in echo density (ED) following contrast injection. METHODS AND RESULTS: An analysis of 437 consecutive patients [58% female, 47 years, interquartile range (IQR) 33-60] who underwent TTCE for the detection of a pulmonary RLS. Using ImageJ (National Institutes of Health), the change in ED was measured for each patient. This method was strongly correlated (Spearman's ρ = 0.89; P < 0.0001) with our standard method based on a four-point grading scale (no, mild, moderate, and severe RLS). In patients without a history of embolotherapy (n = 334), a PAVM was detected with chest computed tomography (CT) in 66 and embolotherapy was judged possible in 35 of these patients. The median increase in ED was higher in the latter: +20.1% (IQR 12.3-34.0) compared to non-treatable PAVM +0.2% (IQR -0.2 to 1.1). The specificity to detect treatable PAVMs increased from 87% to 90% when using the novel method without affecting the sensitivity (of 100%). Using the optimal cut-off value of +4.5% increase in ED, 8/74 (11%) needed chest CT-scans-individuals with a moderate or severe RLS-were no longer required without missing any treatable PAVM. CONCLUSIONS: The use of ED quantification for pulmonary RLS is promising; resulting in a substantial decrease in the number of chest CT scans needed. However, this method and the threshold should be validated in an independent study population.

Hereditary Hemorrhagic Telangiectasia (HHT) and Survival: The Importance of Systematic Screening and Treatment in HHT Centers of Excellence.

Hereditary hemorrhagic telangiectasia (HHT), an autosomal dominant disease, is characterized by telangiectases and arteriovenous malformations (AVMs). Untreated AVMs, especially in the lungs-pulmonary AVMs (PAVMs)-can result in morbidity with a decreased life expectancy. We have investigated whether HHT patients, systematically screened for HHT-related organ involvement and treated if needed, have a similar survival as persons without HHT. We included all individuals screened for HHT between 2004 and 2016 with a genetically or clinically confirmed diagnosis (HHT group) or excluded diagnosis (non-HHT control group). The social security number was used to confirm status as dead or alive in December 2019. We included 717 HHT patients and 471 controls. There was no difference in survival between the HHT and the non-HHT control group. The HHT group had a life expectancy of 75.9 years (95% confidence interval (CI) 73.3-78.6), comparable to the control group (79.3 years, 95% CI 74.8-84.0, Mantel-Cox test: p = 0.29). In conclusion, the life expectancy of HHT patients systematically screened for HHT-related organ involvement and treated if needed in an HHT center of excellence was similar compared to their controls, justifying systematic screening and treatment in HHT patients.

Screening children for pulmonary arteriovenous malformations: Evaluation of 18 years of experience.

BACKGROUND: Hereditary Hemorrhagic Telangiectasia (HHT) is an autosomal dominant disease with multi-systemic vascular dysplasia. Early diagnosis through screening is important to prevent serious complications. How best to screen children of affected parents for pulmonary arteriovenous malformations (PAVMs) is often subject to debate. Transthoracic contrast echocardiogram (TTCE) is considered optimal in screening for PAVMs in adults. Guidelines for the screening of children are not specific, reflecting the lack of scientific evidence on the best method to use. OBJECTIVE: Aims of this study are (i) to evaluate our current screening method, consisting of history, physical examination, pulse oximetry, and chest radiography and (ii) to assess whether postponing more invasive screening for PAVMs until adulthood is safe. METHODS: This is a prospective observational cohort study using a patient database. RESULTS: Over a period of 18 years (mean follow-up 9.21 years, SD 4.72 years), 436 children from HHT families were screened consecutively. A total of 175/436 (40%) children had a diagnosis of HHT. PAVMs were detected in 39/175 (22%) children, 33/39 requiring treatment by embolotherapy. None of the screened children suffered any PAVM-associated complications with this screening method. CONCLUSION: This study shows that a conservative screening method during childhood is sufficient to detect large PAVMs and protect children with HHT for PAVM-related complications. Postponing TTCE and subsequent chest CT scanning until adulthood to detect any smaller PAVMs does not appear to be associated with major risk.

Specific cancer rates may differ in patients with hereditary haemorrhagic telangiectasia compared to controls.

BACKGROUND: Hereditary haemorrhagic telangiectasia (HHT) is inherited as an autosomal dominant trait, affects ~1 in 5,000, and causes multi-systemic vascular lesions and life-limiting complications. Life expectancy is surprisingly good, particularly for patients over 60ys. We hypothesised that individuals with HHT may be protected against life-limiting cancers. METHODS: To compare specific cancer rates in HHT patients and controls, we developed a questionnaire capturing data on multiple relatives per respondent, powered to detect differences in the four most common solid non skin cancers (breast, colorectal, lung and prostate), each associated with significant mortality. Blinded to cancer responses, reports of HHT-specific features allowed assignment of participants and relatives as HHT-subjects, unknowns, or controls. Logistic and quadratic regressions were used to compare rates of specific cancer types between HHT subjects and controls. RESULTS: 1,307 participants completed the questionnaire including 1,007 HHT-subjects and 142 controls. The rigorous HHT diagnostic algorithm meant that 158 (12%) completed datasets were not assignable either to HHT or control status. For cancers predominantly recognised as primary cancers, the rates in the controls generally matched age-standardised rates for the general population. HHT subjects recruited through the survey had similar demographics to controls, although the HHT group reported a significantly greater smoking habit. Combining data of participants and uniquely-reported relatives resulted in an HHT-arm of 2,161 (58% female), and control-arm of 2,817 (52% female), with median ages of 66ys [IQR 53-77] and 77ys [IQR 65-82] respectively. In both crude and age-adjusted regression, lung cancers were significantly less frequent in the HHT arm than controls (age-adjusted odds ratio 0.48 [0.30, 0.70], p = 0.0012). Breast cancer prevalence was higher in HHT than controls (age-adjusted OR 1.52 [1.07, 2.14], p = 0.018). Overall, prostate and colorectal cancer rates were equivalent, but the pattern of colorectal cancer was modified, with a higher prevalence in younger HHT patients than controls. CONCLUSIONS: These preliminary survey data suggest clinically significant differences in the rates of lung, breast and colorectal cancer in HHT patients compared to controls. For rare diseases in which longitudinal studies take decades to recruit equivalent datasets, this type of methodology provides a good first-step method for data collection.

Lifestyle and dietary influences on nosebleed severity in hereditary hemorrhagic telangiectasia.

OBJECTIVES/HYPOTHESIS: To identify factors influencing the severity of epistaxis in hereditary hemorrhagic telangiectasia (HHT). STUDY DESIGN: Participants with and without HHT were recruited from a specialist service and online following advertisement by the HHT Foundation International. Both groups were asked to complete a nonbiased questionnaire. METHODS: The reported effects of specific treatments or lifestyle factors on epistaxis were assigned positive values if beneficial, negative values if detrimental, or zero if "no difference" and were summed to enable statistical analysis. RESULTS: Epistaxis affected 649 of 666 (97%) participants with HHT and was significantly more frequent than in control participants. Specialist invasive treatments were reported as beneficial, laser therapy more frequently than cauterization. Medical treatments commonly used for HHT epistaxis (female hormones, antiestrogens, tranexamic acid, aminocaproic acid, nasal creams, and bevacizumab) also had significantly positive (beneficial) scores. Lifestyle and dietary factors were generally detrimental, but room humidification, nasal lubrication, and saline treatments were all reported as beneficial (95% confidence intervals greater than zero). Multiple food items were volunteered as being detrimental to epistaxis. The most frequently reported items were alcohol (n = 45; 6.8% of participants) and spices (n = 26, 3.9% of participants). Remaining foods reported to exacerbate epistaxis were also found to be high in salicylates (including red wine, spices, chocolate, coffee, and certain fruits), natural antiplatelet activity (garlic, ginger, ginseng, ginkgo biloba, and vitamin E15), or omega-3 acids (oily fish, salmon). CONCLUSIONS: This study supports existing treatments and suggests lifestyle and dietary maneuvers that may also improve nosebleeds in HHT. LEVEL OF EVIDENCE: 2c.