Joint hypermobility

The most unexpected item in Bonaz et al. (2021), and the one that best earns the review’s central architectural claim. A heritable variation in connective tissue — not in brain, not in nerve — turns out to be associated with a specific interoceptive, autonomic and psychiatric phenotype. If the interoceptive system really is one bidirectional hierarchy, this is what a disturbance entering at the bottom should look like.

The phenotype

Variant connective tissue underlies a set of rheumatological conditions related to Ehlers-Danlos syndrome, visibly characterized by hypermobile joints. The associated findings the review reports:

• Higher interoceptive sensitivity in hypermobile individuals, and heightened reactivity of the “interoceptive” insula in brain imaging (Mallorquí-Bagué et al. 2014).
• Anxiety symptoms as the characteristic psychological manifestation — the review frames interoception as implicated specifically in the nonarticular psychological and physical manifestations of hypermobility.
• Dysautonomia, notably postural orthostatic tachycardia syndrome (PoTS), as a common comorbidity “that also mediates affective symptoms.”
• Symptom expression across the cardiovascular, gastrointestinal, respiratory and pelvic systems, and as fibromyalgia (chronic-pain).
• Hypermobility and PoTS “increasingly recognized” in neurodevelopmental disorders, including autism and ADHD (Sinibaldi et al. 2015).

That last item is the one to watch. The wiki holds autism’s interoceptive profile through Quadt et al. as a representational story — low accuracy, high sensibility, an enlarged ITPE, aberrant sensory precision. Bonaz et al. raise the possibility that some of the autism-interoception-anxiety association travels through connective tissue and autonomic reactivity instead. Neither source engages the other and the wiki has no way to adjudicate; recorded as a live alternative reading, not a correction.

Bottom-up, and why that matters here

Most of the wiki’s clinical material runs top-down: a belief, a prior, a precision setting goes wrong and the body follows. Hypermobility runs the other way. The proposed chain is that variant connective tissue produces genuinely different mechanical and autonomic behaviour — vessels, gut, joints — which produces genuinely different afferent traffic, which the interoceptive system must then represent and act on. The anxiety is not a misreading of a normal body; it may be an accurate reading of an unusual one.

This makes hypermobility a useful test case for is-more-interoceptive-awareness-better. Here higher interoceptive sensitivity co-occurs with worse affective outcomes — but not because the signal is being over-attended. The signal is different. Neither “raise awareness” nor “lower it” is obviously the right prescription when the thing being sensed has actually changed.

The stress interaction, and the unexplained minority

The review’s most interesting unresolved observation:

Interaction between psychosocial stress and intrinsic physiological vulnerability might account for why a minority of people with hypermobility become symptomatic.

Hypermobility is common; the full syndromic presentation is not. The proposed moderator is stress, acting two ways: early life trauma and biological stress altering peripheral and central interoception, and — more unusually — the action of stress and sex hormones on the biomechanical functioning of connective tissue itself, contributing to organ and system-level dysfunction. So the hpa-axis is proposed here as acting not only on the brain’s handling of bodily signals but on the mechanical properties of the tissue generating them.

The closing claim is speculative and flagged as such by its own hedging: the effects of stress hormones on brain circuitry “may further crystallize unpredictable, poorly regulated, interoceptive representations into enduring dyshomeostatic patterns of ill-health.” That is a diathesis-stress model with an interoceptive middle term, stated as a hypothesis with one citation (Schulz & Vögele 2015).

Status

Held at one remove and thinly evidenced — a review section by the researcher whose line it is, with no primary source in raw/ and no longitudinal or interventional data. But it is the wiki’s only case of a heritable peripheral tissue variant with a documented interoceptive phenotype, and for that reason it should not be dropped for being small. If an Eccles/Critchley hypermobility paper reaches the queue, this page should be rewritten first-hand. See hugo-critchley.