This review explores the proposal that vulnerability to psychological symptoms, particularly anxiety, originates in constitutional differences in the control of bodily state, exemplified by a set of conditions that include
Joint Hypermobility,
Postural Tachycardia Syndrome and
Vasovagal Syncope. Research is revealing how brain-body mechanisms underlie individual differences in psychophysiological reactivity that can be important for predicting, stratifying and treating individuals with
anxiety disorders and related conditions. One common constitutional difference is
Joint Hypermobility, in which there is an increased range of joint movement as a result of a variant of
collagen.
Joint hypermobility is over-represented in people with anxiety, mood and
neurodevelopmental disorders. It is also linked to stress-sensitive medical conditions such as
irritable bowel syndrome,
chronic fatigue syndrome and
fibromyalgia. Structural differences in "emotional" brain regions are reported in hypermobile individuals, and many people with
joint hypermobility manifest autonomic abnormalities, typically
Postural Tachycardia Syndrome. Enhanced heart rate reactivity during postural change and as recently recognized factors causing vasodilatation (as noted post-prandially, post-exertion and with heat) is characteristic of
Postural Tachycardia Syndrome, and there is a phenomenological overlap with
anxiety disorders, which may be partially accounted for by exaggerated neural reactivity within ventromedial prefrontal cortex. People who experience
Vasovagal Syncope, a heritable tendency to
fainting induced by emotional challenges (and needle/blood
phobia), are also more vulnerable to
anxiety disorders. Neuroimaging implicates brainstem differences in vulnerability to faints, yet the structural integrity of the caudate nucleus appears important for the control of
fainting frequency in relation to parasympathetic tone and anxiety. Together there is clinical and neuroanatomical evidence to show that common constitutional differences affecting autonomic responsivity are linked to psychiatric symptoms, notably anxiety.