Novel Association of the NOTCH Pathway Regulator MIB1 Gene With the Development of Bicuspid Aortic Valve.

Importance: Nonsyndromic bicuspid aortic valve (nsBAV) is the most common congenital heart valve malformation. BAV has a heritable component, yet only a few causative genes have been identified; understanding BAV genetics is a key point in developing personalized medicine. Objective: To identify a new gene for nsBAV. Design, Setting, and Participants: This was a comprehensive, multicenter, genetic association study based on candidate gene prioritization in a familial cohort followed by rare and common association studies in replication cohorts. Further validation was done using in vivo mice models. Study data were analyzed from October 2019 to October 2022. Three cohorts of patients with BAV were included in the study: (1) the discovery cohort was a large cohort of inherited cases from 29 pedigrees of French and Israeli origin; (2) the replication cohort 1 for rare variants included unrelated sporadic cases from various European ancestries; and (3) replication cohort 2 was a second validation cohort for common variants in unrelated sporadic cases from Europe and the US. Main Outcomes and Measures: To identify a candidate gene for nsBAV through analysis of familial cases exome sequencing and gene prioritization tools. Replication cohort 1 was searched for rare and predicted deleterious variants and genetic association. Replication cohort 2 was used to investigate the association of common variants with BAV. Results: A total of 938 patients with BAV were included in this study: 69 (7.4%) in the discovery cohort, 417 (44.5%) in replication cohort 1, and 452 (48.2%) in replication cohort 2. A novel human nsBAV gene, MINDBOMB1 homologue MIB1, was identified. MINDBOMB1 homologue (MIB1) is an E3-ubiquitin ligase essential for NOTCH-signal activation during heart development. In approximately 2% of nsBAV index cases from the discovery and replication 1 cohorts, rare MIB1 variants were detected, predicted to be damaging, and were significantly enriched compared with population-based controls (2% cases vs 0.9% controls; P = .03). In replication cohort 2, MIB1 risk haplotypes significantly associated with nsBAV were identified (permutation test, 1000 repeats; P = .02). Two genetically modified mice models carrying Mib1 variants identified in our cohort showed BAV on a NOTCH1-sensitized genetic background. Conclusions and Relevance: This genetic association study identified the MIB1 gene as associated with nsBAV. This underscores the crucial role of the NOTCH pathway in the pathophysiology of BAV and its potential as a target for future diagnostic and therapeutic intervention.

Assessment of arterial damage in vascular Ehlers-Danlos syndrome: A retrospective multicentric cohort.

Background: Vascular Ehlers-Danlos syndrome (vEDS) is a rare inherited connective tissue disorder due to pathogenic variants in COL3A1 leading to medium-size-artery (MSA) dissection, aneurysm, rupture. Aortic lesions are rarer and less investigated. The objective was to describe the distribution of MSA and aortic lesions and the type of COL3A1 variants in a multicentric cohort of 330 adult vEDS patients. Methods: At the time of the study, 87% were alive, 60.3% were index cases, and 60.0% were women. COL3A1 variants were identified using NGS and/or Sanger sequencing and classified according to functional consequences: 80.6% leading to dominant-negative (DN) and 19.4% leading to haploinsufficiency (HI). Imaging was systematically performed during the initial workup. Carotid mechanics were assessed by echo tracking in a subgroup of patients. Results: Arterial lesions were reported in 82.4% of the patients (N = 272): 83.5% had MSA lesions alone, 3.3% had aortic lesions alone, and 13.2% both. DN variants were associated with a higher prevalence of arterial lesions (P < 0.044), especially in supra-aortic trunks and renal arteries. The prevalence of aortic lesions in HI patients with arterial lesions was higher than that in patients with DN (P 0.027), but not anymore when adjusted for age (P < 0.559). Carotid Young's modulus was lower in patients with DN, in association with the higher incidence of MSA lesions in this group. Conclusion: The prevalence of aortic lesions is not influenced by the COL3A1 genotype when adjusted for age. Patients with DN variant vEDS have a higher frequency of MSA lesions, especially in supra-aortic trunks associated with lower carotid stiffness. These results support optimized care and follow-up for these vulnerable patients.

Is Bicuspid Aortic Valve Morphology Genetically Determined? A Family-Based Study.

Bicuspid aortic valve (BAV) is a common congenital heart disease, with a 10-fold higher prevalence in first-degree relatives. BAV has different phenotypes based on the morphology of cusp fusion. These phenotypes are associated with different clinical courses and prognoses. Currently, the determinants of the valve phenotype are unknown. In this study we evaluated the role of genetics using familial cohorts. Patients with BAV and their first-degree relatives were evaluated by echocardiography. The concordance in BAV phenotype between pairs of family members was calculated and compared with the concordance expected by chance. We then performed a systematic literature review to identify additional reports and calculated the overall concordance rate. During the study period, 70 cases from 31 families and 327 sporadic cases were identified. BAV was diagnosed in 14% of the screened relatives. The proportions of the morphologies identified was: 12.3% for type 0, 66.2% for type 1-LR, 15.4% for type 1-RN, 4.6% for type 1-NL, and 1.5% for type 2. For the assessment of morphologic concordance, we included 120 pairs of first-degree relatives with BAV from our original cohort and the literature review. Concordance was found only in 62% of the pairs which was not significantly higher than expected by chance. In conclusion, our finding demonstrates intrafamilial variability in BAV morphology, suggesting that morphology is determined by factors other than Mendelian genetics. As prognosis differs by morphology, our findings may suggest that clinical outcomes may vary even between first-degree relatives.

Management and outcomes of hypertrophic cardiomyopathy in young adults.

BACKGROUND: Management of young adults with hypertrophic cardiomyopathy (HCM) is challenging. AIMS: To evaluate the profile of young adults (16-25 years) with HCM included in the French prospective HCM registry. METHODS: Patients were compared according to occurrence of major adverse cardiac events (MACE), comprising sudden cardiac death (SCD) events (implantable cardioverter defibrillator [ICD] discharge, SCD, sustained ventricular tachycardia), atrial fibrillation/embolic stroke, heart failure hospitalisation and unexplained syncope, at a mean follow-up of 4.4±2.2 years. RESULTS: At baseline, among 61 patients (20.5±3.0 years; 16 women, 26.2%), 13 (21.3%) had a prophylactic ICD, 24.6% a family history of SCD, 29.5% obstruction, 86.0% magnetic resonance imaging myocardial fibrosis, 11.8% abnormal exercise blood pressure and 52.8% a European Society of Cardiology (ESC) 5-year SCD score<4% (24.5%≥6%). At follow-up, 15 patients (24.6%; seven women; all with fibrosis) presented 17 MACE, comprising: SCD events (n=7, 41.2%; including three patients with an ICD, five with at least one SCD major classical risk factor and an ESC score≥5% and two with no risk factors and an ESC score<4%); atrial fibrillation/stroke (n=6, 35.3%); heart failure (n=1, 5.9%); syncope (n=3, 17.6%). An ICD was implanted in 11 patients (four for secondary prevention), but in only 61.5% of patients with a score≥6%. Only obstruction significantly increased MACE risk (odds ratio 3.96; P=0.035), with a non-significant trend towards a lower risk in men (OR 0.29; P=0.065). CONCLUSIONS: In young adults with HCM, MACE are common in the short term, especially in obstructive HCM and women, mostly arrhythmic in origin. Prophylactic ICD implantation is frequent and does not strictly follow the guidelines, while the use of European/USA guidelines is helpful but imperfect in identifying SCD risk.

Psychosocial Impact of Predictive Genetic Testing in Hereditary Heart Diseases: The PREDICT Study.

Predictive genetic testing (PGT) is offered to asymptomatic relatives at risk of hereditary heart disease, but the impact of result disclosure has been little studied. We evaluated the psychosocial impacts of PGT in hereditary heart disease, using self-report questionnaires (including the State-Trait Anxiety Inventory) in 517 adults, administered three times to the prospective cohort (PCo: n = 264) and once to the retrospective cohort (RCo: n = 253). The main motivations for undergoing PGT were "to remove doubt" and "for their children". The level of anxiety increased between pre-test and result appointments (p <0.0001), returned to baseline after the result (PCo), and was moderately elevated at 4.4 years (RCo). Subjects with a history of depression or with high baseline anxiety were more likely to develop anxiety after PGT result (p = 0.004 and p <0.0001, respectively), whatever it was. Unfavourable changes in professional and/or family life were observed in 12.4% (PCo) and 18.7% (RCo) of subjects. Few regrets about PGT were expressed (0.8% RCo, 2.3% PCo). Medical benefit was not the main motivation, which emphasises the role of pre/post-test counselling. When PGT was performed by expert teams, the negative impact was modest, but careful management is required in specific categories of subjects, whatever the genetic test result.

Communication of genetic information to at-risk relatives during the multidisciplinary monitoring of vascular Ehlers-Danlos syndrome in a French referral clinic.

Vascular Ehlers-Danlos syndrome (vEDS) is a rare inherited disorder leading to arterial, digestive, and uterine complications due to pathogenic COL3A1 variants. Identification of causal variants allows family screening, provided that relatives have previously been informed, according to a 2013 French Decree. The aims of our study were to assess the communication of genetic information to at-risk relatives, the impact of diagnosis disclosure and to highlight a possible link between the experience of vEDS patients and ability to communicate about genetic information. A total of n = 51 vEDS adult probands answered a questionnaire during a clinical visit. Communication to relatives was considered effective if the proband gave information to some or all first-degree relatives and considered easily achieved if it was disclosed to all relatives less than a month after the diagnosis and without difficulty. Personal and family vEDS experiences of probands were also assessed. Effective communication of information to relatives was remarkably high (98%). Siblings were the most frequently informed relatives (82%). Women informed their at-risk relatives of genetic family screening faster (p = .006) and easier (p = .004) than men. There was no difference in the disclosure of information to relatives before and after 2013 in our multidisciplinary clinic. Regarding the lived experience of vEDS patients, they felt anxious (78%) at diagnosis disclosure but also considered this diagnosis as an opportunity to start a medical follow-up (82%) putting an end to diagnosis delay. Our findings highlight for the first time that the ability to easily inform at-risk first-degree relatives is related to the relief felt during vEDS-positive diagnosis disclosure (p = .04). In order to improve the communication of genetic information to relatives, we believe that psychological support should systematically be part of the multidisciplinary monitoring, just as medical follow-up and genetic counseling.

Classical Ehlers-Danlos syndrome with a propensity to arterial events: A new report on a French family with a COL1A1 p.(Arg312Cys) variant.

Ehlers-Danlos syndromes (EDS) are a clinically and genetically heterogeneous group of connective tissue disorders. Overlapping features including arterial aneurysms/dissections in both classical and vascular EDS are a major challenge in the clinical diagnosis of these subtypes. The COL1A1 p.(Arg312Cys) variant leads to a phenotype of classical EDS with a propensity to arterial complications. Our report describes a two-generation family with one individual presenting with a dissection of the right external iliac artery. The primary suspicion of vascular EDS with the unsatisfactory identification of a COL3A1 benign variant was secondarily readjusted with the identification of COL1A1 p.(Arg312Cys) variant. This raises the question of the association of COL1A1 p.(Arg312Cys) with arterial complications and the need for a gene panel including not only the usual genes tested in search of classical or vascular EDS but also COL1A1.

Vascular Ehlers-Danlos Syndrome: Long-Term Observational Study.

BACKGROUND: Vascular Ehlers-Danlos syndrome (vEDS) is a rare genetic connective tissue disorder secondary to pathogenic variants within the COL3A1 gene, resulting in exceptional arterial and organ fragility and premature death. The only published clinical trial to date demonstrated the benefit of celiprolol on arterial morbimortality. OBJECTIVES: The authors herein describe the outcomes of a large cohort of vEDS patients followed ≤17 years in a single national referral center. METHODS: All patients with molecularly confirmed vEDS were included in a retrospective cohort study. After an initial work-up, patients were treated or recommended for treatment with celiprolol (≤400 mg/day) in addition to usual care and scheduled for yearly follow-up. vEDS-related events and deaths were collected and recorded for each patient. RESULTS: Between 2000 and 2017, 144 patients (median age at diagnosis 34.5 years, 91 probands) were included in this study. After a median follow-up of 5.3 years, overall patient survival was high (71.6%; 95% confidence interval: 50% to 90%) and dependent on the type of COL3A1 variant, age at diagnosis, and medical treatment. At the end of the study period, almost all patients (90.3%) were treated with celiprolol alone or in combination. More than two-thirds of patients remained clinically silent, despite a large number (51%) with previous arterial events or arterial lesions at molecular diagnosis. Patients treated with celiprolol had a better survival than others (p = 0.0004). The observed reduction in mortality was dose-dependent: the best protection was observed at the dose of 400 mg/day versus <400 mg/day (p = 0.003). During the period surveyed, the authors observed a statistically significant difference in the ratio of hospitalizations for acute arterial events/hospitalizations for regular follow-up before and after 2011. CONCLUSIONS: In this long-term survey, vEDS patients exhibited a low annual occurrence of arterial complications and a high survival rate, on which the overall medical care seems to have a positive influence.

Copy number variation analysis in bicuspid aortic valve-related aortopathy identifies TBX20 as a contributing gene.

Bicuspid aortic valve (BAV) is the most common congenital heart defect (CHD), affecting 1-2% of the population. BAV is associated with thoracic aortic aneurysms (TAAs). Deleterious copy number variations (CNVs) were found previously in up to 10% of CHD cases. This study aimed at unravelling the contribution of deleterious deletions or duplications in 95 unrelated BAV/TAA patients. Seven unique or rare CNVs were validated, harbouring protein-coding genes with a role in the cardiovascular system. Based on the presence of overlapping CNVs in patients with cardiovascular phenotypes in the DECIPHER database, the identification of similar CNVs in whole-exome sequencing data of 67 BAV/TAA patients and suggested topological domain involvement from Hi-C data, supportive evidence was obtained for two genes (DGCR6 and TBX20) of the seven initially validated CNVs. A rare variant burden analysis using next-generation sequencing data from 637 BAV/TAA patients was performed for these two candidate genes. This revealed a suggestive genetic role for TBX20 in BAV/TAA aetiology, further reinforced by segregation of a rare TBX20 variant with the phenotype within a BAV/TAA family. To conclude, our results do not confirm a significant contribution for deleterious CNVs in BAV/TAA as only one potentially pathogenic CNV (1.05%) was identified. We cannot exclude the possibility that BAV/TAA is occasionally attributed to causal CNVs though, or that certain CNVs act as genetic risk factors by creating a sensitised background for BAV/TAA. Finally, accumulative evidence for TBX20 involvement in BAV/TAA aetiology underlines the importance of this transcription factor in cardiovascular disease.

Accuracy of Clinical Diagnostic Criteria for Patients With Vascular Ehlers-Danlos Syndrome in a Tertiary Referral Centre.

BACKGROUND: Vascular Ehlers-Danlos syndrome is a rare inherited connective tissue disease secondary to mutations within the COL3A1 gene. The diagnosis of vascular Ehlers-Danlos syndrome is challenging, and patient selection for genetic testing relies on diagnostic criteria, which have never been evaluated. METHODS: All patients seen at a dedicated tertiary referral center for a suspicion of vascular Ehlers-Danlos syndrome between January 2001 and March 2016 were retrospectively included in a diagnostic accuracy study. Major and minor diagnostic criteria of the Villefranche classification were tested for sensitivity, specificity, positive and negative predictive values, according to results of genetic testing. RESULTS: N=519 patients were eligible for analysis dividing into n=384 probands and n=135 relatives. A pathogenic COL3A1 variant was identified in n=165 (31.8%) patients. The Villefranche criteria were met for n=248 patients with a sensitivity of 79% (95% CI, 0.72-0.85) and a negative predictive value of 87% (95% CI, 0.83-0.91). Diagnostic accuracy was highest for symptomatic probands (sensitivity 92%; negative predictive value 95%) with limited specificity (60%). Probands ≤25 years had the worst diagnostic performance. The revised diagnostic Criteria (2017) were less accurate than the Villefranche classification (overall diagnostic odds-ratio, 4.17 versus 7.8; probands diagnostic odds-ratio, 4.04 versus 18.1; and probands ≤25 years diagnostic odds-ratio, 2.36 versus 5.1) mainly due to a lack of sensitivity. CONCLUSIONS: The Villefranche criteria provide accurate detection of symptomatic probands in specialized practice but have limited specificity. The revised diagnostic criteria for vascular Ehlers-Danlos syndrome have increased specificity, but its overall performance is poorer. The early clinical diagnosis of probands without family history is not addressed by both diagnostic classifications.

Accuracy of Clinical Diagnostic Criteria for Patients with Vascular Ehlers-Danlos Syndrome in a Tertiary Referral Centre.

BACKGROUND: Vascular Ehlers-Danlos syndrome (vEDS) is a rare inherited connective tissue disease secondary to mutations within the COL3A1 gene. The diagnosis of vEDS is challenging and patient selection for genetic testing relies on diagnostic criteria, which have never been evaluated. METHODS: All patients seen at a dedicated tertiary referral centre for a suspicion of vEDS between January 2001 and March 2016 were retrospectively included in a diagnostic accuracy study. Major and minor diagnostic criteria of the Villefranche classification were tested for sensitivity (Se), specificity (Sp), positive and negative predictive values (PPV, NPV), according to results of genetic testing. RESULTS: N=519 patients were eligible for analysis dividing into n=384 probands and n=135 relatives. A pathogenic COL3A1 variant was identified in n=165 (31.8%) patients. The Villefranche criteria were met for n=248 patients with a Se of 79% (95%CI: 0.72-0.85) and a NPV of 87% (95%CI: 0.83-0.91). Diagnostic accuracy was highest for symptomatic probands (Se 92%; NPV 95%) with limited Sp (60%). Probands {less than or equal to}25 years had the worst diagnostic performance. The revised diagnostic Criteria (2017) were less accurate than the Villefranche classification (overall Diagnostic odds-ratio (DOR) 4.17 vs. 7.8, probands DOR 4.04 vs. 18.1; probands {less than or equal to}25 years DOR 2.36 vs. 5.1), mainly due to a lack of Se. CONCLUSIONS: The Villefranche criteria provide accurate detection of symptomatic probands in specialized practice, but have limited Sp. The revised diagnostic criteria for vEDS have increased Sp, but its overall performance is poorer. The early clinical diagnosis of probands without family history is not addressed by both diagnostic classifications.

Frequency of de novo variants and parental mosaicism in vascular Ehlers-Danlos syndrome.

PURPOSE: Vascular Ehlers-Danlos syndrome (vEDS) is a rare inherited autosomal dominant disorder caused by COL3A1 pathogenic variants. A high percentage of de novo cases has been suggested. Part of it could be due to parental mosaicism, but its frequency is unknown. METHODS: This retrospective study included a large series of COL3A1-confirmed vEDS probands with family information. The frequency of de novo cases was evaluated and the distribution of the type of variants was compared according to the mode of inheritance. The COL3A1 mosaicism was studied by deep targeted next- generation sequencing (NGS) from parental blood DNA. RESULTS: Out of 177 vEDS probands, 90 had a negative family history, suggesting a high rate (50.8%) of de novo pathogenic variants, enriched in the more severe COL3A1 variants (no null variant). Among those, both parental DNA were available in 36 cases and one parental DNA in 18 cases. NGS detected only one mosaicism from maternal blood DNA (allelic ratio 18%), which was confirmed in saliva (allelic ratio 22%). CONCLUSION: vEDS is characterized by a high frequency of de novo pathogenic variants. Parental mosaicism is rare (2-3%), but should be systematically searched with targeted NGS, taking into account its importance in genetic counseling.

Identification of a new VHL exon and complex splicing alterations in familial erythrocytosis or von Hippel-Lindau disease.

Chuvash polycythemia is an autosomal recessive form of erythrocytosis associated with a homozygous p.Arg200Trp mutation in the von Hippel-Lindau (VHL) gene. Since this discovery, additional VHL mutations have been identified in patients with congenital erythrocytosis, in a homozygous or compound-heterozygous state. VHL is a major tumor suppressor gene, mutations in which were first described in patients presenting with VHL disease, which is characterized by the development of highly vascularized tumors. Here, we identify a new VHL cryptic exon (termed E1') deep in intron 1 that is naturally expressed in many tissues. More importantly, we identify mutations in E1' in 7 families with erythrocytosis (1 homozygous case and 6 compound-heterozygous cases with a mutation in E1' in addition to a mutation in VHL coding sequences) and in 1 large family with typical VHL disease but without any alteration in the other VHL exons. In this study, we show that the mutations induced a dysregulation of VHL splicing with excessive retention of E1' and were associated with a downregulation of VHL protein expression. In addition, we demonstrate a pathogenic role for synonymous mutations in VHL exon 2 that altered splicing through E2-skipping in 5 families with erythrocytosis or VHL disease. In all the studied cases, the mutations differentially affected splicing, correlating with phenotype severity. This study demonstrates that cryptic exon retention and exon skipping are new VHL alterations and reveals a novel complex splicing regulation of the VHL gene. These findings open new avenues for diagnosis and research regarding the VHL-related hypoxia-signaling pathway.

Mutation spectrum in the ABCC6 gene and genotype-phenotype correlations in a French cohort with pseudoxanthoma elasticum.

PURPOSE: Pseudoxanthoma elasticum (PXE) is an autosomal recessive disorder caused by variants in the ABCC6 gene. Ectopic mineralization of connective tissues leads to skin, eye, and cardiovascular manifestations with considerable phenotypic variability of unknown cause. We aimed to identify genotype-phenotype correlations in PXE. METHODS: A molecular analysis was performed on 458 French PXE probands clinically evaluated using the Phenodex score (PS). Variant topographic analysis and genotype-phenotype correlation analysis were performed according to the number and type of identified variants. RESULTS: Complete molecular analysis of 306 cases allowed the identification of 538 mutational events (88% detection rate) with 142 distinct variants, of which 66 were novel. Missense variant distribution was specific to some regions and residues of ABCC6. For the 220 cases with a complete PS, there was a higher prevalence of eye features in Caucasian patients (P = 0.03) and more severe eye and vascular phenotype in patients with loss-of-function variants (P = 0.02 and 0.05, respectively). Nephrolithiases and strokes, absent from the PS, were prevalent features of the disorder (11 and 10%, respectively). CONCLUSION: We propose an updated PS including renal and neurological features and adaptation of follow-up according to the genetic and ethnic status of PXE-affected patients.Genet Med advance online publication 19 January 2017.

Risk assessment of maternally inherited SDHD paraganglioma and phaeochromocytoma.

BACKGROUND: Germline mutations in the SDHD tumour suppressor gene (11q23.1) predispose to phaeochromocytomas and paragangliomas (PPGL) mainly on a paternal transmission. However, PPGL have been recently reported in three carriers of a maternally inherited SDHD mutation. OBJECTIVE: To assess the risk of PPGL occurrence on maternal transmission of SDHD mutation. METHODS: Pedigrees of 80 SDHD-related families have been reviewed. 35 asymptomatic subjects carrying a maternally transmitted SDHD mutation were identified. 20 of them accepted to benefit from a PPGL imaging screening. RESULTS: A unique histologically proven biochemically negative phaeochromocytoma has been diagnosed in a 35-year-old woman. Molecular investigations carried out on tumour tissue revealed that the loss of heterozygosity encompassed the paternally derived q arm and the maternally derived p arm of chromosome 11. CONCLUSIONS: This study demonstrates that the risk of developing PPGL for a subject carrying a germline SDHD mutation on the maternal allele remains a rare scenario but does exist. Our data suggest an adjustment of current genetic counselling and clinical care recommendations for at-risk subjects. A targeted familial genetic test should be proposed from the age of 18 years to every subject having a mother carrying a germline SDHD mutation and a first medical workup, including imaging, should be recommended to SDHD-positive mutation carriers.

The type of variants at the COL3A1 gene associates with the phenotype and severity of vascular Ehlers-Danlos syndrome.

Vascular Ehlers-Danlos syndrome (vEDS) is a rare and severe autosomal dominant disorder caused by variants at the COL3A1 gene. Clinical characteristics and course of disease of 215 molecularly proven patients (146 index cases and 69 relatives) were analysed. We found 126 distincts variants that were divided into five groups: (1) Glycine substitutions (n=71), (2) splice-site and in-frame insertions-deletions (n=36), (3) variants leading to haplo-insufficiency (n=7), (4) non-glycine missense variants within the triple helix (n=4 variants), and (5) non-glycine missense variants or in-frame insertions-deletions, in the N- or C-terminal part of the protein (n=8). Overall, our cohort confirmed the severity of the disease with a median age at first complication of 29 years (IQR 22-39), the most frequent being arterial (48%) and digestive (24%) ruptures. Groups 2 and 1 were significantly more severe than groups 3-5, with extreme median ages at first major complication of 23-47 years. Patients of groups 3-5 had a less typical phenotype and remarkably absence of digestive events. The distribution of glycine-replacing amino acids was strongly biased towards more destabilizing residues of the collagen assembly. Thus the natural course of vEDS and the clinical phenotype of patients are influenced by the type of COL3A1 variant. This study also confirms that patients with variants located in the C- and N-termini or leading to haplo-insufficiency have milder course of the disease and less prevalent diagnostic criteria. These findings may help refine diagnostic strategy, genetic counselling and clinical care.