Heterozygous THBS2 Pathogenic Variants Cause Ehlers-Danlos Syndrome with Prominent Vascular Features in Humans and Mice

Paper Background

Ehlers-Danlos syndrome (EDS) is a group of connective tissue disorders caused by mutations in collagen and collagen-related genes. These disorders present in various forms and can be classified into 14 different types based on their clinical features. Classical EDS typically manifests as joint hypermobility, skin hyperextensibility, and skin fragility, while other types may involve vascular or skeletal problems. Vascular EDS (vEDS) is characterized by aneurysms and arterial dissections, caused by heterozygous pathogenic variants in the COL3A1 gene. However, vascular involvement can also occur in other types of EDS. The clinical overlap emphasizes the need for precise molecular diagnosis in affected individuals.

Paper Source

This paper, titled “Heterozygous THBS2 Pathogenic Variants Cause Ehlers-Danlos Syndrome with Prominent Vascular Features in Humans and Mice,” is authored by Noam Hadar, Omri Porgador, Idan Cohen, and others. These authors are affiliated with institutions such as the Multidisciplinary Research Institute at Ben-Gurion University of the Negev, the Department of Radiology at Soroka Medical Center, and the Sackler Faculty of Medicine at Tel Aviv University in Israel. The paper was published in the European Journal of Human Genetics in 2024, with the DOI https://doi.org/10.1038/s41431-024-01559-1.

Research Workflow

Clinical Evaluation and Sample Collection

The research team first identified a new form of EDS through clinical and histopathological analysis of a three-generation family. Affected individuals exhibited prominent vascular features, joint hypermobility with frequent dislocations, atrophic scarring, prolonged bleeding time, and age-related aortic dilation and rupture.

Genetic Analysis

Researchers extracted DNA from peripheral blood leukocytes and used whole-exome sequencing to identify potential pathogenic gene variants. After aligning sequencing data to the reference genome, internal software and filtering strategies were used to screen for variants with a frequency lower than 0.1% in multiple databases. Eventually, a heterozygous mutation in the THBS2 gene (NM_003247.5:c.2686T>C, p.Cys896Arg) was identified.

Animal Model

To confirm the pathogenicity of this mutation, the research team introduced this heterozygous mutation into mouse ears using the CRISPR/Cas9 system. The resulting knock-in mice exhibited phenotypes similar to humans, including pathological changes observable in morphological, histological, and transmission electron microscopy analyses. Additionally, bleeding time experiments showed significantly prolonged bleeding times in mice, consistent with human patients.

Main Research Findings

Clinical Discoveries

In the study, affected individuals exhibited joint hypermobility, multiple joint dislocations (including jaw, shoulder, hip, knee, and ankle joints), tendon ruptures, easy bruising, slow wound healing, and lower limb muscle fatigue after exercise. Vascular imaging showed large artery dilation, such as aortic arch dilation, in affected individuals, with no evidence of cardiomyopathy.

Histopathological Analysis

Histological examination of skin biopsies from affected individuals showed highly disorganized collagen fibers in the reticular dermis, along with vascular dilation and abnormal morphology of fibroblasts and endothelial cells. In mouse experiments, histological and electron microscopy analyses also revealed similar abnormal features.

Genetic and Functional Analysis

Through whole-exome sequencing, a heterozygous mutation in the THBS2 gene was identified as the cause of EDS in this family. THBS2 encodes thrombospondin-2, a secreted trimeric matrix protein that directly binds to matrix metalloproteinase 2 (MMP2) and mediates its clearance. Loss of THBS2 function impairs MMP2 clearance, increasing MMP2-mediated proteoglycan cleavage, leading to extracellular matrix abnormalities similar to those observed in this study.

Conclusion

This study reveals a new form of EDS caused by heterozygous THBS2 mutations, characterized by elements of classical EDS with prominent vascular features. By generating a mouse model carrying the human mutation, the research team further confirmed the disease phenotype caused by this mutation. The critical role of THBS2 in maintaining extracellular matrix integrity and tissue repair makes it a target for understanding and treating such connective tissue disorders.

Research Significance

Scientific Value

By identifying and describing a new genetic variant and corresponding phenotype, this study provides new insights into the molecular basis of Ehlers-Danlos syndrome. This has important implications for future molecular diagnostics and personalized treatment.

Application Value

The animal model generated in this study can be used for further research on the role of THBS2 in connective tissue disorders, helping to develop targeted treatments for this specific variant. Additionally, the potential preventive measures proposed in the study (such as 5-methyltetrahydrofolate supplementation) provide new ideas for clinical management.

Research Highlights

1. Identified a new form of EDS and its causative gene variant;
2. Generated a mouse model carrying the human mutation, verifying the pathogenicity of this mutation;
3. Proposed and verified the key role of THBS2 in maintaining extracellular matrix integrity.

Abstract

This study systematically and comprehensively identified a new type of Ehlers-Danlos syndrome caused by heterozygous mutations in the THBS2 gene. Through clinical and histopathological analysis of human patients, gene sequencing, and the generation and validation of mouse models, the research team thoroughly revealed the specific role of this mutation in tissue structure and its impact on vascular homeostasis. The results not only enrich the molecular basis of connective tissue disorders but also provide a solid foundation for further therapeutic research.