Mutations causing premature termination codons discriminate and generate cellular and clinical variability in HHT.

ABSTRACT: For monogenic diseases caused by pathogenic loss-of-function DNA variants, attention focuses on dysregulated gene-specific pathways, usually considering molecular subtypes together within causal genes. To better understand phenotypic variability in hereditary hemorrhagic telangiectasia (HHT), we subcategorized pathogenic DNA variants in ENG/endoglin, ACVRL1/ALK1, and SMAD4 if they generated premature termination codons (PTCs) subject to nonsense-mediated decay. In 3 patient cohorts, a PTC-based classification system explained some previously puzzling hemorrhage variability. In blood outgrowth endothelial cells (BOECs) derived from patients with ACVRL1+/PTC, ENG+/PTC, and SMAD4+/PTC genotypes, PTC-containing RNA transcripts persisted at low levels (8%-23% expected, varying between replicate cultures); genes differentially expressed to Bonferroni P < .05 in HHT+/PTC BOECs clustered significantly only to generic protein terms (isopeptide-bond/ubiquitin-like conjugation) and pulse-chase experiments detected subtle protein maturation differences but no evidence for PTC-truncated protein. BOECs displaying highest PTC persistence were discriminated in unsupervised hierarchical clustering of near-invariant housekeeper genes, with patterns compatible with higher cellular stress in BOECs with >11% PTC persistence. To test directionality, we used a HeLa reporter system to detect induction of activating transcription factor 4 (ATF4), which controls expression of stress-adaptive genes, and showed that ENG Q436X but not ENG R93X directly induced ATF4. AlphaFold accurately modeled relevant ENG domains, with AlphaMissense suggesting that readthrough substitutions would be benign for ENG R93X and other less rare ENG nonsense variants but more damaging for Q436X. We conclude that PTCs should be distinguished from other loss-of-function variants, PTC transcript levels increase in stressed cells, and readthrough proteins and mechanisms provide promising research avenues.

End of Life Care for Unplanned Vascular Admissions.

BACKGROUND: Unplanned vascular admissions have a high mortality. Previous studies have indicated that end of life care (EoLC) among this group of patients is low but there exist limited data on EoLC in the United Kingdom. The aim of this study was to evaluate the quality and predictors of EoLC for unplanned vascular admissions to a tertiary center in the United Kingdom. METHODS: This was a retrospective single-center cohort study of unplanned vascular surgery admissions from August 1, 2019 to January 22, 2020. Data on patient demographics, markers of quality of palliative care, mortality, and cause of death of unplanned admission to the vascular surgery department were collected from hospital and general practitioner records and evaluated against EoLC to evaluate predictors and efficacy of EoLC. Quality of palliative care markers included documentation of preferred place of death and care priorities, time spent in hospital and the intensive care unit toward the end of life, and realization of documented care objectives. EoLC input was defined as a dedicated palliative care consultation (PCC) by a palliative care professional, medical doctor, surgeon, or advanced care practitioner. We also conducted a subgroup analysis of patients within this group with chronic limb-threatening ischemia (CLTI), diabetic foot, and ruptured aortic aneurysms, as all patients in this group should be offered EoLC according to international guidelines. RESULTS: One-hundred and fifty patients were included. Median age at presentation was 70.5 years, and the cohort consisted of mostly men (72%). CLTI (31%) was the most common reason for admission. Surgical intervention was carried out in 60% of patients. Two-year mortality was 36%, and pneumonia (22%) was the most common cause of death. Seven percent of patients received PCC, which occurred a median of 10 days before death. Only a minority of patients had preferred place of care/death (14%), care priorities (37%), and family involvement during advance care planning (17%) documented in their notes; 29% of patients had Recommended Summary Plan for Emergency Care and Treatment forms in place. A diagnosis of left ventricular systolic dysfunction, chronic kidney disease, and increasing age predicted Recommended Summary Plan for Emergency Care and Treatment form completion. Patients with PCC were more likely to have advance care planning, but this did not translate into improvements in the other markers of quality of palliative and, consequently, EoLC. CONCLUSIONS: EoLC was insufficient and of low quality despite a high mortality in this group. Clinical guidelines and pathways are needed to ensure these patients are considered for EoLC and those with CLTI, diabetic foot sepsis or ruptured abdominal aortic aneurysms are offered it by default. Further research is needed to help identify vascular patients who would benefit from EoLC earlier to improve quality at end of life.

Pathogenic Variant Frequencies in Hereditary Haemorrhagic Telangiectasia Support Clinical Evidence of Protection from Myocardial Infarction.

Hereditary haemorrhagic telangiectasia (HHT) is a vascular dysplasia inherited as an autosomal dominant trait, due to a single heterozygous loss-of-function variant, usually in ACVRL1 (encoding activin receptor-like kinase 1 [ALK1]), ENG (encoding endoglin [CD105]), or SMAD4. In a consecutive single-centre series of 37 positive clinical genetic tests performed in 2021-2023, a skewed distribution pattern was noted, with 30 of 32 variants reported only once, but ACVRL1 c.1231C>T (p.Arg411Trp) identified as the disease-causal gene in five different HHT families. In the same centre's non-overlapping 1992-2020 series where 110/134 (82.1%) HHT-causal variants were reported only once, ACVRL1 c.1231C>T (p.Arg411Trp) was identified in nine further families. In a 14-country, four-continent HHT Mutation Database where 181/250 (72.4%) HHT-causal variants were reported only once, ACVRL1 c.1231C>T (p.Arg411Trp) was reported by 12 different laboratories, the adjacent ACVRL1 c.1232G>A (p.Arg411Gln) by 14, and ACVRL1 c.1120C>T (p.Arg374Trp) by 18. Unlike the majority of HHT-causal ACVRL1 variants, these encode ALK1 protein that reaches the endothelial cell surface but fails to signal. Six variants of this type were present in the three series and were reported 6.8-25.5 (mean 8.9) times more frequently than the other ACVRL1 missense variants (all p-values < 0.0039). Noting lower rates of myocardial infarction reported in HHT, we explore potential mechanisms, including a selective paradigm relevant to ALK1's role in the initiating event of atherosclerosis, where a plausible dominant negative effect of these specific variants can be proposed. In conclusion, there is an ~9-fold excess of kinase-inactive, cell surface-expressed ACVRL1/ALK1 pathogenic missense variants in HHT. The findings support further examination of differential clinical and cellular phenotypes by HHT causal gene molecular subtypes.