Comorbidities
The hEDS-POTS-MCAS "Trifecta" Claim, Examined
We're not clinicians. This page lays out what the research supports and doesn't support about the hEDS-POTS-MCAS cluster people often call "the trifecta," so you can weigh the term against the evidence yourself.
The co-occurrence of these three conditions shows up often enough in patient populations that it has its own nickname. That doesn't mean the underlying medical connection between them is settled science. Treating it as settled is where the trifecta framing gets ahead of what's been shown.
Is the hEDS-POTS-MCAS Trifecta Real? What Survey Data Shows
A 2025 survey of 84 women with HSD or hEDS found that 58.3% also reported POTS (postural orthostatic tachycardia syndrome), 32.1% also reported MCAS (mast cell activation syndrome), and 25% reported all three together. That's a notable clustering, and it's a reasonable thing to know going into a doctor's appointment. If you have hEDS and are dealing with dizziness on standing or unexplained allergic-type reactions, you're not an outlier for wondering if they're connected.
Where the Trifecta Claim Outruns the Evidence
A separate 2025 multicenter retrospective review in the Journal of Allergy and Clinical Immunology, along with a related Mayo Clinic cohort, looked for a confirmed association between MCAS and hEDS/POTS using strict diagnostic criteria for MCAS. They didn't find one.
The gap between these findings comes down to diagnosis. MCAS has specific lab-based diagnostic criteria, including elevated tryptase during a symptomatic episode, and many people carrying an MCAS label in patient communities and even in some clinical settings haven't been confirmed against those criteria. Self-reported or clinically assumed MCAS is not the same data point as lab-confirmed MCAS, and the survey above didn't distinguish between the two.
So Is the Trifecta Real or Not?
These two findings sit in real tension, and we're not going to paper over that: a survey found MCAS reported by roughly a third of people with hEDS/HSD, while a separate multicenter review using strict diagnostic criteria found no confirmed association between MCAS and hEDS/POTS at all. The diagnostic-criteria gap described above is one possible explanation, but it's an explanation, not a resolution. The disagreement between what gets reported and what strict testing confirms is still open. "Trifecta" describes a symptom pattern people frequently report together. Whether it describes a proven mechanism is a separate, unsettled question.
What to do with this
If you have hEDS and symptoms that suggest POTS or MCAS, the useful next step is a proper diagnostic workup for each condition on its own terms, not an assumption that having one means you have all three. A cardiologist or autonomic specialist can evaluate for POTS with objective testing like a tilt-table study.
For MCAS specifically, that means seeing an allergist or immunologist who can test against the recognized diagnostic criteria, rather than accepting the label from symptom overlap alone. If a confirmed diagnosis doesn't hold up, that's useful information too. It means your symptoms need a different explanation, not that they're being dismissed.
Sources referenced on this page
- 012025 survey, n=84 women with HSD/hEDS: POTS and MCAS co-occurrence rates (link not yet sourced)
- 02Multicenter retrospective review, Journal of Allergy and Clinical Immunology (2025) (link not yet sourced)
- 03Mayo Clinic cohort study (2025): MCAS diagnostic criteria in hEDS/POTS patients (link not yet sourced)