Introduction

What is Ehlers-Danlos Syndrome or EDS?

Ehlers-Danlos Syndrome is a heritable connective tissue disorder characterised by skin hyperextensibility, joint hypermobility, and tissue fragility.¹ This condition is caused by genetic changes that affect connective tissue.¹

What are the types of EDS?

Ehlers-Danlos syndrome is classified based on the 13 subtypes and 19 different sets of genes involved in the maintenance and synthesis of collagen and extracellular matrix.^2,3

Hypermobile EDS (hEDS), classical EDS (cEDS) and vascular EDS (vEDS) are among the most common types of EDS. The prevalence of EDS is estimated to be between 1 in 5000 and 1 in 2,00,000, based on the EDS subtype.²

Clinical diagnosis of EDS

Clinical diagnosis of EDS includes medical and family history of the patient, physical examination focusing on the skin elasticity, and other physical symptoms and genetic testing. No tests are available to confirm Hypermobile EDS (hEDS).¹ The diagnosis is made on the basis of medical history and physical examination using the Beighton Scale.  

Genetic Testing and Molecular diagnosis in EDS

Genetic testing is used to identify and analyse genetic variations in DNA. The results can be used for the confirmation of specific genetic disorders. Usually, a genetic sample like blood or saliva is collected and sent to a lab. The lab will perform tests like DNA extraction, PCR amplification for the library preparation, DNA sequencing to identify genetic variants and report back information about a person’s genetic variants and whether they are known to be associated with any disease.²

There is no specific molecular test available for Hypermobile EDS (hEDS), genetic testing is essential for the other types of EDS, which have known genetic causes. 

Genetic testing and molecular diagnosis include Sanger sequencing, next-generation sequencing (NGS), whole-exome sequencing (WES), whole-genome sequencing (WGS), multi-gene panels, and copy number variant (CNV) analysis. Genetic panels or sequencing of specific genes are common approaches, while whole genome or exome sequencing is used for the identification of new variants.²

Next Generation Sequencing (NGS) in EDS Diagnosis 

Next-generation sequencing is one of the most widely used tools for diagnosing EDS. NGS helps in the identification of genetic variations in the genes which are associated with EDS. 

• Targeted Sequencing (Gene Panels): Targeted sequencing can be used for the analysis of a single gene or a group of genes, known as a gene panel
• Whole-Exome Sequencing (WES): WES examines protein-coding regions of the genome, and identifies genetic variants
• Whole-Genome Sequencing (WGS): WGS examines the entire genome, which helps in identifying potential disease-causing variants
• Sanger Sequencing: Sanger sequencing can be used to confirm NGS results and ensure complete coverage of target sequences
• Copy Number Variant (CNV): A copy number variant (CNV) detection test can be used to identify large duplications and deletions in case no pathogenic variants are identified through sequencing

Challenges and Advances in Molecular Diagnosis

Hypermobile EDS (hEDS): A diagnostic gap

• hEDS is the most prevalent form of EDS. Its molecular genetic testing is challenging due to the unknown genetic basis⁴
• In 2018, “Hypermobile Ehlers-Danlos Genetic Evaluation” (HEDGE) was created by the International EDS Society (https://www.ehlers-danlos.com). It is a collaborative effort to identify genetic markers for hEDS. The HEDGE study aims to recruit, screen and undertake thousands of individuals who have been diagnosed with hEDS by the most recent clinical criteria established in 2017 for research purposes

Identification of variants of unknown significance (VUS)

• Next-generation sequencing (NGS) is used for the identification of  EDS subtypes; broad genetic testing can identify misleading variants known as variants of unknown significance VUS, leading to uncertainty, potential misdiagnosis, and unnecessary treatments¹
• Future diagnostics may include long-read sequencing, RNA sequencing, optical genome mapping, and expanded integrated omics approaches

Overlapping phenotypes

• The clinical features of EDS subtypes can overlap significantly with each other and with other heritable connective tissue disorders (HCTDs), making clinical diagnosis difficult¹

Future Perspectives

Some of the elements that need to be considered are enhancement of diagnostic tests, clinical guides and personalised medicine for EDS and hEDS. Increasing the awareness among the patients and the physicians for improved disease management and treatment. Utilisation of AI and machine learning for better treatment and data interpretation.

Summary

Ehlers-Danlos Syndrome is a group of connective tissue disorders which is characterised by symptoms like joint hypermobility, hyperextensibility of the skin, and connective tissue fragility. Based on the clinical features and genetic basis there are 13 different subtypes of EDS. The genetic cause of Hypermobile EDS (hEDS) which is the most common form of EDS is unidentified and at present can not be diagnosed. Other subtypes of EDS can be identified using the different genetic and molecular approaches like next-generation sequencing, multi-gene panel and copy number variant (CNV) analysis. The challenges associated with the genetic and molecular diagnosis of EDS include the unknown genetic basis of hEDS, clinical overlap with other connective tissue disorders,  risk of identification of variants of unknown significance (VUS). Initiatives like  “Hypermobile Ehlers Danlos Genetic Evaluation” (HEDGE) launched by the International EDS Society for the identification of genetic markers for hEDS can be help understand hEDS and find the diagnostic test. Advanced sequencing, AI tools, biomarker identification can be future breakthroughs.