Impact of heterozygous ALK1 mutations on the transcriptomic response to BMP9 and BMP10 in endothelial cells from hereditary hemorrhagic telangiectasia and pulmonary arterial hypertension donors

Heterozygous activin receptor-like kinase 1 (ALK1) mutations are associated with two vascular diseases: hereditary hemorrhagic telangiectasia (HHT) and more rarely pulmonary arterial hypertension (PAH). Here, we aimed to understand the impact of ALK1 mutations on BMP9 and BMP10 transcriptomic responses in endothelial cells. Endothelial colony-forming cells (ECFCs) and microvascular endothelial cells (HMVECs) carrying loss of function ALK1 mutations were isolated from newborn HHT and adult PAH donors, respectively. RNA-sequencing was performed on each type of cells compared to controls following an 18 h stimulation with BMP9 or BMP10. In control ECFCs, BMP9 and BMP10 stimulations induced similar transcriptomic responses with around 800 differentially expressed genes (DEGs). ALK1-mutated ECFCs unexpectedly revealed highly similar transcriptomic profiles to controls, both at the baseline and upon stimulation, and normal activation of Smad1/5 that could not be explained by a compensation in cell-surface ALK1 level. Conversely, PAH HMVECs revealed strong transcriptional dysregulations compared to controls with > 1200 DEGs at the baseline. Consequently, because our study involved two variables, ALK1 genotype and BMP stimulation, we performed two-factor differential expression analysis and identified 44 BMP9-dysregulated genes in mutated HMVECs, but none in ECFCs. Yet, the impaired regulation of at least one hit, namely lunatic fringe (LFNG), was validated by RT-qPCR in three different ALK1-mutated endothelial models. In conclusion, ALK1 heterozygosity only modified the BMP9/BMP10 regulation of few genes, including LFNG involved in NOTCH signaling. Future studies will uncover whether dysregulations in such hits are enough to promote HHT/PAH pathogenesis, making them potential therapeutic targets, or if second hits are necessary.

Genome sequencing identify chromosome 9 inversions disrupting ENG in 2 unrelated HHT families

Hereditary hemorrhagic telangiectasia (HHT), also known as Rendu-Osler-Weber disease, is a dominant inherited vascular disorder. The clinical diagnosis is based on the Curaçao criteria and pathogenic variants in the ENG and ACVRL1 genes are responsible for most cases of HHT. Four families with a negative targeted gene panel and selected by a multidisciplinary team were selected and whole-genome sequencing was performed according to the recommendations of the French National Plan for Genomic Medicine. Structural variations were confirmed by standard molecular cytogenetic analysis (FISH). In two families with a definite diagnosis of HHT, we identified two different paracentric inversions of chromosome 9, both disrupting the ENG gene. These inversions are considered as pathogenic and causative for the HHT phenotype of the patients. This is the first time structural variations are reported to cause HHT. As such balanced events are often missed by exon-based sequencing (panel, exome), structural variations may be an under-recognized cause of HHT. Genome sequencing for the detection of these events could be suggested for patients with a definite diagnosis of HHT and in whom no causative pathogenic variant was identified.

[Hereditary hemorrhagic telangiectasia]

Hereditary hemorrhagic telangiectasia, also known as Rendu-Osler - Weber disease, is a rare, autosomal dominant vascular disease, with prevalence of 1/5,000. The condition is characterized by muco-cutaneous telangiectasias, which are responsible for a hemorrhagic syndrome of variable severity, as well as arteriovenous malformations (AVMs) appearing in the lungs, the liver, and the nervous system. They can be the source of shunts, which may be associated with high morbidity (neurological ischemic stroke, brain abscess, high-output heart failure, biliary ischemia…). It is therefore crucial to establish a clinical diagnosis using the Curaçao criteria or molecular diagnosis based on genetic analysis of the ENG, ACVRL1, SMAD4 and GDF2 genes. In most cases, multidisciplinary management allows patients to have normal life expectancy. Advances in interventional radiology and better understanding of the pathophysiology of angiogenesis have resulted in improved therapeutic management. Anti-angiogenic treatments, such as bevacizumab (BVZ, an anti-VEGF antibody), have proven to be effective in cases involving bleeding complications and severe liver damage with cardiac repercussions. Other anti-angiogenic agents are currently being investigated, including tyrosine kinase inhibitors.

The European Rare Disease Network for HHT Frameworks for management of hereditary haemorrhagic telangiectasia in general and speciality care

Hereditary haemorrhagic telangiectasia (HHT) is a complex, multisystemic vascular dysplasia affecting approximately 85,000 European Citizens. In 2016, eight founding centres operating within 6 countries, set up a working group dedicated to HHT within what became the European Reference Network on Rare Multisystemic Vascular Diseases. By launch, combined experience exceeded 10,000 HHT patients, and Chairs representing 7 separate specialties provided a median of 24 years' experience in HHT. Integrated were expert patients who focused discussions on the patient experience. Following a 2016-2017 survey to capture priorities, and underpinned by more than 40 monthly meetings, and new data acquisitions, VASCERN HHT generated position statements that distinguish expert HHT care from non-expert HHT practice. Leadership was by specialists in the relevant sub-discipline(s), and 100% consensus was required amongst all clinicians before statements were published or disseminated. One major set of outputs targeted all healthcare professionals and their HHT patients, and include the new Orphanet definition; Do's and Don'ts for common situations; Outcome Measures suitable for all consultations; COVID-19; and anticoagulation. The second output set span aspects of vascular pathophysiology where greater understanding will assist organ-specific specialist clinicians to provide more informed care to HHT patients. These cover cerebral vascular malformations and screening; mucocutaneous telangiectasia and differential diagnosis; anti-angiogenic therapies; circulatory interplays between anaemia and arteriovenous malformations; and microbiological strategies to counteract loss of normal pulmonary capillary function. Overall, the integrated outputs, and documented current practices, provide frameworks for approaches that augment the health and safety of HHT patients in diverse health-care settings.

Tranexamic acid for epistaxis in hereditary hemorrhagic telangiectasia patients: a European cross-over controlled trial in a rare disease

BACKGROUND

Hereditary hemorrhagic telangiectasia (HHT) is a genetic disorder associated with abnormal angiogenesis and disabling epistaxis. Tranexamic acid (TA) has been widely used in the treatment of these severe bleeds but with no properly designed trial.

OBJECTIVES

To demonstrate the efficacy of TA in epistaxis in HHT patients and to explore its safety of use.

PATIENTS/METHODS

A randomized, placebo-controlled, double-blind, cross-over trial was conducted. Participants were randomized to receive TA (3 g a day) then placebo or the opposite sequence. The main analysis compared intra-individual mean duration of epistaxis under TA vs. placebo on a log scale. The primary outcome was the mean duration of epistaxis per month, assessed with specific grids to be completed by participants. The number of epistaxis episodes was recorded as a secondary outcome.

RESULTS

A total of 118 randomized patients contributed to the statistical analysis. The mean duration of epistaxis per month was significantly shorter with TA than placebo (0.19 on the log scale; SD = 0.07; P = 0.005), corresponding to a decrease of 17.3% (15.7 min) in the duration of epistaxis per month (CI 95%, 5.5-27.6). The median number of epistaxis episodes per month was 22.1 episodes in the placebo arm vs. 23.3 episodes in the TA arm. No thrombophlebitis was observed.

CONCLUSIONS

In the ATERO study, we demonstrated a significant decrease in the duration of epistaxis in HHT patients taking TA. No safety issues were recorded in our cohort of patients.

Immunological abnormalities associated with hereditary haemorrhagic telangiectasia

OBJECTIVE

Hereditary haemorrhagic telangiectasia (HHT) is a genetic disorder related to mutations in one of the coreceptors to the transforming growth factor-β superfamily (ALK1 or endoglin). Besides the obvious vascular symptoms (epistaxis and arteriovenous malformations), patients have an unexplained high risk of severe bacterial infections. The aim of the study was to assess the main immunological functions of patients with HHT using the standard biological tests for primary immunodeficiencies.

DESIGN, SETTING AND SUBJECTS

A prospective single-centre study of 42 consecutive adult patients with an established diagnosis of HHT was conducted at the National French HHT Reference Center (Lyon). Lymphocyte subpopulations and proliferation capacity, immunoglobulin levels and neutrophil and monocyte phagocytosis, oxidative burst and chemotaxis were assessed.

RESULTS

Innate immunity was not altered in patients with HHT. With regard to adaptive immunity, significant changes were seen in immunological parameters: primarily, a lymphopenia in patients with HHT compared with healthy control subjects affecting mean CD4 (642 cells μL(-1) vs. 832 cells μL(-1) , P < 0.001), CD8 (295 cells μL(-1) vs. 501 cells μL(-1) , P < 0.0001) and natural killer (NK) cells (169 cells μL(-1) vs. 221 cells μL(-1) , P < 0.01), associated with increased levels of immunoglobulins G and A. This lymphopenia mainly concerned naïve T cells. Proliferation capacities of lymphocytes were normal. Lymphopenic patients had a higher frequency of iron supplementation but no increase in infection rate. Lower levels of immunoglobulin M and a higher rate of pulmonary arteriovenous malformations were found amongst patients with a history of severe infection.

CONCLUSIONS

Patients with HHT exhibit immunological abnormalities including T CD4, T CD8 and NK cell lymphopenia and increased levels of immunoglobulins G and A. The observed low level of immunoglobulin M requires further investigation to determine whether it is a specific risk factor for infection in HHT.

[Pregnancy and Ehlers-Danlos vascular syndrome: patients' care and complications]

INTRODUCTION

Elhers-Danlos vascular syndrome type IV (EDS4) is a hereditary pathology of the connective tissue responsible for an increased risk of lethal arterial, uterine and digestive complications during and after pregnancy.

PATIENTS AND METHODS

We describe the obstetrical care, the nature and frequency of complications related to pregnancy of patients with EDS4 and their relatives.

RESULTS

Twenty-seven pregnancies were studied including 23 deliveries, 18 vaginal deliveries and five caesarean, no maternal death and two major life-threatening complications (8.7%) were recorded which could be directly linked to EDS4 (rupture of the biscupid valve pillar after vaginal delivery and a rupture of the caecum after a prophylactic caesarean). Ten deliveries underwent epidural anesthesia without complication. Six perineal injuries (33.3%) were observed.

CONCLUSION

Pregnancy in patient with EDS4 needs obstetrical cares in a special unit's motivated medical team with intensive care and surgical disponibilities.

Hereditary hemorrhagic telangiectasia: from molecular biology to patient care

SUMMARY

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant vascular disorder characterized by severe and recurrent nosebleeds, mucocutaneous telangiectases, and, in some cases, life-threatening visceral arteriovenous malformations of various types, including pulmonary, hepatic, cerebral, and spinal. Gastrointestinal telangiectases are frequent and may cause severe bleeding. HHT type 1 results from mutations in ENG on chromosome 9 (coding for endoglin), and HHT type 2 results from mutations in ACVRL1 on chromosome 12 (coding for activin receptor-like kinase 1). Mutations of either of these two genes account for most clinical cases. In addition, mutations in MADH4 (encoding SMAD4), which cause a juvenile polyposis/HHT overlap syndrome, have been described, and recently, an HHT3 locus on chromosome 5 (5q31.3-5q32) has been reported. The mutated genes in HHT encode proteins that modulate transforming growth factor-beta superfamily signaling in vascular endothelial cells. Management of patients has changed considerably in the last 20 years, in terms of both treatment and the prevention of complications. The goal of this review was to describe the underlying molecular and cellular physiopathology, explore clinical and genetic diagnostic strategies for HHT, and present clinical management recommendations in order to treat symptomatic disease and to screen for vascular malformations.

The mutational spectrum of human malignant autosomal recessive osteopetrosis

Human malignant infantile osteopetrosis (arOP; MIM 259700) is a genetically heterogeneous autosomal recessive disorder of bone metabolism, which, if untreated, has a fatal outcome. Our group, as well as others, have recently identified mutations in the ATP6i (TCIRG1) gene, encoding the a3 subunit of the vacuolar proton pump, which mediates the acidification of the bone/osteoclast interface, are responsible for a subset of this condition. By sequencing the ATP6i gene in arOP patients from 44 unrelated families with a worldwide distribution we have now established that ATP6i mutations are responsible for approximately 50% of patients affected by this disease. The vast majority of these mutations (40 out of 42 alleles, including seven deletions, two insertions, 10 nonsense substitutions and 21 mutations in splice sites) are predicted to cause severe abnormalities in the protein product and are likely to represent null alleles. In addition, we have also analysed nine unrelated arOP patients from Costa Rica, where this disease is apparently much more frequent than elsewhere. All nine Costa Rican patients bore either or both of two missense mutations (G405R and R444L) in amino acid residues which are evolutionarily conserved from yeast to humans. The identification of ATP6i gene mutations in two families allowed us for the first time to perform prenatal diagnosis: both fetuses were predicted not to be affected and two healthy babies were born. This study contributes to the determination of genetic heterogeneity of arOP and allows further delineation of the other genetic defects causing this severe condition.

X-linked anhidrotic ectodermal dysplasia with immunodeficiency is caused by impaired NF-kappaB signaling

The molecular basis of X-linked recessive anhidrotic ectodermal dysplasia with immunodeficiency (EDA-ID) has remained elusive. Here we report hypomorphic mutations in the gene IKBKG in 12 males with EDA-ID from 8 kindreds, and 2 patients with a related and hitherto unrecognized syndrome of EDA-ID with osteopetrosis and lymphoedema (OL-EDA-ID). Mutations in the coding region of IKBKG are associated with EDA-ID, and stop codon mutations, with OL-EDA-ID. IKBKG encodes NEMO, the regulatory subunit of the IKK (IkappaB kinase) complex, which is essential for NF-kappaB signaling. Germline loss-of-function mutations in IKBKG are lethal in male fetuses. We show that IKBKG mutations causing OL-EDA-ID and EDA-ID impair but do not abolish NF-kappaB signaling. We also show that the ectodysplasin receptor, DL, triggers NF-kappaB through the NEMO protein, indicating that EDA results from impaired NF-kappaB signaling. Finally, we show that abnormal immunity in OL-EDA-ID patients results from impaired cell responses to lipopolysaccharide, interleukin (IL)-1beta, IL-18, TNFalpha and CD154. We thus report for the first time that impaired but not abolished NF-kappaB signaling in humans results in two related syndromes that associate specific developmental and immunological defects.

Growth hormone deficiency caused by pituitary stalk interruption in Fanconi's anemia

Fanconi's anemia can be associated with growth retardation. We describe biologic growth hormone deficiency, isolated or associated with thyrotropin abnormality, and pituitary stalk interruption syndrome on magnetic resonance imaging of 5 patients with Fanconi's anemia. Growth hormone treatment produced catch-up growth in all cases. These findings suggest a common genetic origin.

[High-dose chemotherapy in relapse of medulloblastoma in young children]

Craniospinal irradiation is the gold standard treatment used in non metastatic medulloblastoma as prophylaxis against central nervous system (CNS) metastases. However, given the severe late effects caused by this procedure in children under 3 years of age, most pediatric oncologists are currently treating these patients with conventional chemotherapy in order to postpone or even avoid irradiation. In the French Society of Pediatric Oncology (SFOP) this attitude has been adopted since 1990. Among the patients treated without radiotherapy, 20 relapsed while on conventional chemotherapy and were entered in a study of high-dose chemotherapy (HDC) followed by autologous bone marrow transplantation (ABMT). Their median age at diagnosis was 23 months (range: 5-71 months) and the relapse occurred at a median time of 6.3 months after the initiation of chemotherapy. Complete surgical removal of the local relapse was the first treatment in 4/20 patients who were not evaluable for response. Sixteen of the 20 patients had measurable disease at the primary site (9 patients), or at metastatic sites (3 patients) or both (4 patients). The conditioning regimen consisted of combination busulfan 600 mg/m2 over 4 days and thiotepa 900 mg/m2 over 3 days. After recovery from aplasia, patients with a local relapse received local radiotherapy limited to posterior fossa. Among the 16 patients with measurable disease, 6 complete responses, 6 partial responses, 3 non response, were observed following HDC (response rate 75%). One patient was not evaluable. For the 20 patients, the event free survival (EFS) is 50%. Among the surviving patients, the median follow-up is 39.5 months post BMT (range: 21-92 months). Ten patients who developed a local relapse or local progression are alive with non evidence of disease (NED) without craniospinal irradiation. Among the 7 patients who developed a metastases or progression of metastases, only 1 is alive. Toxicity was high but manageable. One complication-related death occurred 1 month post BMT. With a 75% response rate, this HDC proved to be very efficient in relapsed medulloblastoma. A longer follow-up is necessary to demonstrate whether, after a local relapse, HDC could replace craniospinal irradiation as prophylaxis against CNS metastases.

Will high dose chemotherapy followed by autologous bone marrow transplantation supplant cranio-spinal irradiation in young children treated for medulloblastoma?

Cranio-spinal irradiation is the gold standard treatment used in non metastatic medulloblastoma as prophylaxis against central nervous system (CNS) metastases. However, given the severe late effects caused by this procedure in children under 3 years of age, most pediatric oncologists are currently treating these patients with conventional chemotherapy in order to postpone or even avoid irradiation. In the French Society of Pediatric Oncology (SFOP) this attitude has been adopted since 1987. Among the patients treated without radiotherapy, 20 relapsed while on conventional chemotherapy and were entered in a study of high-dose chemotherapy (HDC) followed by ABMT. Their median age at diagnosis was 23 months (R5-71) and the relapse occurred at a median time of 6.3 months after the initiation of chemotherapy. Complete surgical removal of the local relapse was the first treatment in 4/20 patients who were not evaluable for response. Sixteen of the twenty patients had measurable disease at the primary site (9 patients), or at metastatic sites (3 patients) or both (4 patients). The conditioning regimen consisted of combination Busulfan 600 mg/m2 over 4 days and Thiotepa 900 mg/m2 over three days. After recovery from aplasia, patients with a local relapse received local radiotherapy limited to posterior fossa.

RESULTS

among the 16 patients with measurable disease, 6 CR, 6 PR, 3 NR, were observed following HDC (response rate 75%). One patient was not evaluable. For the 20 patients, the EFS is 50%. Among the surviving patients, the median follow up is 31 months post BMT (R12-82). Ten patients who developed a local relapse or local progression are alive with NED without craniospinal irradiation. Among the 7 patients who developed metastases or progression of metastases, only one is alive. Toxicity was high but manageable: the median duration of granulocytopenia < 0.5 x 109/l and thrombocytopenia < 50 x 10(9)/l was 13 and 41 days respectively. Bacteremia was documented in 4 cases. Grade > 2 mucositis and diarrhea were observed in 60% of patients. One complication-related death occurred 1 month post BMT.

CONCLUSION

With a 75% response rate, this HDC proved to be very efficient in relapsed medulloblastoma. A longer follow up is necessary to demonstrate whether, after a local relapse, HDC could replace craniospinal irradiation as prophylaxis against CNS metastases.