The 2017 international classification of the Ehlers-Danlos syndromes

EDS is not one condition. It is a family of heritable connective tissue disorders that share the feature of structurally compromised connective tissue but differ in genetic cause, inheritance pattern, severity, and systemic complications. The 2017 international classification by Malfait and colleagues — published as a supplement to the American Journal of Medical Genetics and representing the work of a broad international consortium of EDS experts — established 13 distinct subtypes, replacing the 1997 Villefranche criteria that had previously organized the field. For anyone navigating an EDS diagnosis, the 2017 classification is the reference point: it defines what the subtypes are, what distinguishes them, and — critically — which subtypes have confirmed genetic causes and which do not. That last distinction has profound clinical implications that persist today.

The 13 Subtypes: A Framework for a Heterogeneous Condition

The 2017 classification defines 13 EDS subtypes. Each is characterized by specific diagnostic criteria, a known or suspected inheritance pattern (autosomal dominant, autosomal recessive, or X-linked), and where the molecular basis has been established, the specific gene or genes involved. The subtypes vary dramatically in prevalence, from hEDS which may account for 80-90% of EDS diagnoses, to the rarer subtypes which may affect only a few hundred families worldwide.

Classical EDS (cEDS) is caused by mutations in COL5A1 or COL5A2, genes that encode type V collagen, and is characterized by skin hyperextensibility, atrophic scarring, and joint hypermobility. Vascular EDS (vEDS) is caused by mutations in COL3A1, encoding type III collagen, and carries the highest medical risk in the EDS family — the friable blood vessels and hollow organs that characterize it can rupture without warning, and vEDS carries significant mortality risk. Kyphoscoliotic EDS involves mutations affecting lysyl hydroxylase 1, producing progressive scoliosis and muscular hypotonia. Arthrochalasia EDS involves mutations in COL1A1 or COL1A2 and produces severe joint hypermobility with congenital bilateral hip dislocation. The remaining subtypes cover a spectrum of rarer presentations with specific biochemical defects in collagen biosynthesis, modification, or structural proteins.

For most patients and many clinicians, the practical landscape of the 13 subtypes is that 12 of them have identified genetic causes and can be confirmed with genetic testing, while one — the most common — does not.

Hypermobile EDS: The Most Common Subtype Without a Genetic Marker

Hypermobile EDS (hEDS) is by far the most prevalent EDS subtype. Estimates suggest it accounts for the large majority of EDS diagnoses, though prevalence data are uncertain given the diagnostic challenges the condition presents. hEDS is characterized by generalized joint hypermobility, musculoskeletal complications including joint pain and instability, and a cluster of associated features including skin manifestations, autonomic dysfunction, fatigue, and in many patients significant functional impairment.

What distinguishes hEDS from every other EDS subtype is the absence of an identified genetic cause. Despite decades of research, no consistent molecular marker — no gene mutation, no specific protein abnormality — has been found that reliably identifies hEDS patients and distinguishes them from people with benign joint hypermobility who do not have the functional and pain burden of hEDS. Diagnosis is made entirely on clinical criteria: the 2017 classification requires the presence of generalized joint hypermobility (assessed by Beighton score), specific associated clinical features, a positive family history or musculoskeletal complications, and the exclusion of other conditions that might explain the findings.

This means that hEDS diagnosis depends entirely on a clinician who knows what to look for, applying clinical criteria correctly, in a patient who has not been excluded by a misdiagnosis that came earlier. There is no confirmatory blood test. There is no genetic test. There is no biomarker. The diagnosis is clinical, and its accuracy depends entirely on clinical expertise with a condition that most clinicians rarely encounter.

Why the Absence of a Genetic Marker Creates Structural Problems

The diagnostic situation in hEDS mirrors, and in some respects amplifies, the diagnostic situation in ME/CFS. Without a molecular confirmation, hEDS diagnosis is vulnerable to the same systemic barriers that affect any condition diagnosed on clinical criteria alone. Clinicians unfamiliar with the condition miss it — they attribute the joint pain to fibromyalgia, the fatigue to depression or deconditioning, the autonomic symptoms to anxiety. Insurance systems that require objective confirmation for coverage of specialist evaluation or treatment may not recognize a purely clinical diagnosis as sufficient. Research cohorts recruited on clinical criteria may include patients with different underlying biologies, contaminating research findings and making replication harder.

Patients carry the burden of demonstrating a condition that the current diagnostic infrastructure cannot definitively confirm. They face the same dismissal that ME/CFS patients face — the absence of a confirmatory test is treated as evidence that the condition does not exist or is psychologically mediated, rather than as evidence of a gap in what current medicine can measure. The research on perceived stigma and physiological outcomes applies to hEDS patients in the same way it applies to ME/CFS patients — the social environment of disbelief has real physiological consequences through the same autonomic threat pathways.

The Relationship Between hEDS and Dysautonomia

The 2017 classification noted autonomic dysfunction as an associated feature of hEDS, though it is not a diagnostic criterion. The Eccles research on hypermobility, neurodivergence, and autonomic symptoms and the Scheper proprioception research provide mechanistic frameworks for why dysautonomia is common in hEDS: degraded proprioceptive signaling from lax connective tissue impairs the interoceptive feedback that the autonomic nervous system depends on for accurate regulatory output.

This connection means that for many hEDS patients, the full clinical picture includes not just joint pain and instability but the entire spectrum of orthostatic intolerance — POTS-like symptoms, fatigue, cognitive impairment, post-exertional worsening. The 2017 classification placed hEDS as a connective tissue condition. The clinical reality of many hEDS patients is that they are also managing a dysautonomia condition. The two diagnoses are not independent comorbidities. They share a mechanistic substrate in impaired sensory feedback from structurally compromised connective tissue.

Using the 2017 Classification in Clinical Encounters

For patients and clinicians, the 2017 Malfait classification serves several practical functions. It is the authoritative reference for what EDS subtypes exist, what criteria define them, and what distinguishes them. When a patient suspects EDS and a clinician is uncertain what they are evaluating, the 2017 criteria provide the structured clinical assessment that organizes the diagnosis. When a patient has received a diagnosis and wants to understand what subtype they have and what its genetic basis is, this classification provides the framework.

For hEDS patients specifically, the classification also provides the formal documentation that their condition has no genetic test — which is information relevant to clinical encounters where a clinician demands "proof" that does not exist. The condition is not unconfirmable because it is not real. It is unconfirmable by current molecular testing because the molecular basis has not yet been found. Those are different statements with different clinical implications. The 2017 classification states clearly that hEDS lacks an identified genetic cause, which places the diagnostic limitation where it belongs: in the current state of knowledge, not in the validity of the condition.