Patrick Long, MD | Medical Geneticist and Family Physician—SequenceMD
If you’ve spent any time navigating the world of Ehlers-Danlos syndromes (EDS), you’ve probably encountered the word monogenic. It shows up in genetics reports, research papers, and clinical conversations, often without much explanation. But this word carries real weight for people living with types of EDS. Understanding it can change the way you think about your diagnosis, your care, and your future.
One Gene, One Answer
Monogenic means that a condition is caused by a change, called a variant, in a single gene. Not a cluster of genes. Not a vague predisposition. One gene. When we identify a disease-causing variant in that gene, we can trace the condition back to a specific molecular event.
The 2017 International Classification recognized thirteen types of EDS, and more recent evidence describes up to fourteen. Molecular causes have now been identified for twelve of the thirteen types recognized in 2017, involving at least twenty different genes. Each of the monogenic types is tied to a specific gene or a small set of genes involved in the structure or processing of collagen or related connective tissue proteins. These include genes like COL5A1 and COL5A2 in classical EDS, COL3A1 in vascular EDS, and TNXB in classical-like EDS, among others. Each gene tells a different biological story. Each one produces a different pattern of risks, features, and symptoms.
Why This Matters to You
While the monogenic types of EDS can be diagnosed using clinical diagnostic criteria, a genetic diagnosis can provide information that a clinical label alone cannot. Monogenic diagnoses help explain the underlying cause of the condition by identifying the specific protein that is affected. That knowledge can support a more precise understanding of variant-specific features, inheritance patterns, and care considerations.
At SequenceMD, knowing whether someone has vascular EDS (vEDS) versus classical EDS (cEDS) isn’t an academic exercise. It directly shapes what we monitor, what concerns us, and what we can offer reassurance about. It informs surgical decisions. It guides family planning conversations. It gives your care team a map instead of a compass.
For families, a monogenic finding also means we can look at the specific variant and understand whether it was inherited or arose for the first time in the patient, something geneticists call a de novo variant. That distinction matters enormously for parents, for siblings, and for future generations.
When the Picture Looks the Same, but the Story Is Different
Here’s where things get both fascinating and important. Many of the monogenic EDS types share features with one another, and with conditions that aren’t EDS at all. Joint hypermobility, fragile skin, easy bruising, chronic pain: these symptoms can appear across multiple types of EDS, in other connective tissue disorders like Loeys-Dietz or Marfan syndromes, and even in some monogenic neuromuscular and skeletal conditions that have nothing to do with collagen. This kind of overlap is what geneticists call phenotypic similarity, and it’s one of the most common reasons people receive an incomplete or incorrect diagnosis.
A condition that closely resembles another but arises from a completely different genetic cause is called a phenocopy. We see this regularly in practice. Two people can walk into a clinic with strikingly similar symptoms and walk out with two entirely different genetic diagnoses, because the molecular mechanisms are distinct even when the surface presentation is not. Without genetic testing, we may be treating a phenocopy as though it were the condition it mimics. That’s not just imprecise. For some types of EDS, particularly vascular EDS, it can mean missing life-altering surveillance recommendations. While phenocopy rates in EDS specifically have not been as extensively studied as in some other genetic conditions, the principle is well established across medical genetics and underscores the importance of molecular confirmation.
Two people can walk into a clinic with strikingly similar symptoms and walk out with two entirely different genetic diagnoses
And the complexity doesn’t stop at mimicry. EDS can co-occur with other genetic conditions. It can contribute to a clinical picture that also includes an entirely separate diagnosis. In the course of comprehensive genetic testing, we sometimes uncover incidental or secondary findings: variants in genes unrelated to the original question that nonetheless carry important implications for a patient’s health. This is the current reality of connective tissue genetics. EDS may mimic, contribute to, and co-occur with countless other conditions. The borders between diagnoses are not always clean, and testing illuminates territory that clinical assessment alone cannot reach.
The Power of the Right Test, Ordered the Right Way
This is why molecular confirmation, genetic testing that identifies the specific gene and variant, is so important. It’s not a formality. It’s not a luxury. It’s the tool that moves us from pattern recognition to precision. It separates conditions that look alike but behave differently, and it allows clinicians to tailor surveillance to the actual biology, not just the symptom profile.
But not all genetic testing is created equal, and context matters enormously. When a geneticist performs comprehensive clinical phenotyping before ordering testing, carefully evaluating a patient’s features system by system, reviewing their history, and considering their family background, the result is a fundamentally different kind of evaluation. The clinician can account for the full range of indications, construct a thorough differential diagnosis, and select the testing strategy that gives the best chance of finding the answer. In some cases, that means a targeted gene panel; in others, it means broader genome sequencing. The choice depends on clinical context, and an experienced geneticist is best positioned to make that call.
This matters because genetic tests have measurable performance characteristics. Sensitivity describes how reliably a test detects a condition when it’s truly present. Negative predictive value tells us how confidently we can trust a negative result, how assured we can be that a condition has been ruled out when testing comes back normal. Both improve when the right test is ordered for the right clinical question, by a clinician who has done the work of understanding the full picture before the sample is ever drawn. It’s worth noting that test performance varies by EDS type and clinical presentation. For vascular EDS, for example, clinical diagnostic criteria show sensitivity around 79–92% depending on whether the patient is a symptomatic proband or a broader referral. In children with suspected EDS, diagnostic yield studies have shown that only a subset meet clinical criteria, and even among those, a meaningful proportion remain without molecular confirmation after comprehensive testing. A genetic test is only as powerful as the clinical thinking behind it.
It’s also important to understand that genetic testing sometimes returns results that are not immediately clear-cut. Variants of uncertain significance, or VUS, are genetic changes whose impact on health is not yet fully understood. These are common—found in roughly one in four patients tested for connective tissue disorders—and they require expert interpretation. A VUS does not mean a diagnosis, but it also doesn’t mean the testing was uninformative. It means the science is still catching up. This is one of the reasons why genetic testing is most valuable when it’s guided by a geneticist who can place the result in clinical context and help patients understand what it means for them.
Resolve, Discover, Prevent
For the patients we work with, genetic clarity often brings something less tangible but equally real: resolution. Many people in the EDS community have spent years, sometimes decades, in a diagnostic odyssey, seeing specialist after specialist, collecting partial answers that never quite fit together. A monogenic diagnosis doesn’t erase that journey, but it can give it a destination. It can turn a frustrating accumulation of symptoms into a coherent story with a name, a mechanism, and a path forward.
But genetic testing doesn’t only resolve; it discovers. In the process of looking for one answer, comprehensive testing can reveal secondary or incidental findings, actionable genetic information that a patient and their care team would not have found otherwise. And it prevents: by identifying a condition early and precisely, we can implement surveillance, adjust management, and in some cases intervene before complications ever develop.
Genetic testing offers substantial benefits: diagnostic resolution, identification of co-occurring conditions, and prevention of complications through appropriate surveillance. It also has limitations, including the possibility of variants of uncertain significance and the need for expert interpretation. But for most patients with features suggestive of monogenic types of EDS, the benefits of appropriately selected genetic testing are significant and, in our clinical judgment, clearly favor testing. This is the standard of care toward which all of medicine is moving, and the EDS community stands to benefit enormously.
A Brighter, More Curious Future
Understanding what “monogenic” means is more than vocabulary. It’s an invitation to ask better questions of your clinicians, of your genetic test results, and of the research that shapes our understanding of these conditions. Every year, our ability to identify and characterize these variants improves. Every year, the map gets more detailed.
You deserve that level of detail. People deserve a diagnosis that doesn’t stop at the surface.
SequenceMD offers global access to genetic specialists for evaluation, testing, and counseling for complex, rare, and inherited conditions. Visit sequencemd.com
