Not really:
IBS has now been shown to involve certain antibodies, and so may be an autoimmune disease.
Interstitial cystitis and
overactive bladder are linked to dysgunction of the GAG layer in the bladder.
Raynaud's disease is involves problems in regulation of blood vessel dilation, and involves an overreaction by the sympathetic nervous system (which contracts blood vessels).
Allergies are related to autoimmunity, and involve immune dysfunction.
Attention deficit hyperactivity disorder,
depression,
generalized anxiety disorder and
eating disorders are mental health conditions which will involve the brain.
Low T3 syndrome is an endocrine disorder, and may be autoimmune.
Hashimoto's disease is an autoimmune disorder.
Prolapsed mitral valve involves connective tissue, since this heart valve is made from connective tissue. But studies have found viral infections in the heart valve of such patients, and we know that infections can trigger the release of MMP enzymes which weaken connective tissue.
Metabolic syndrome involves abdominal obesity, high blood pressure, high blood sugar, etc.
Sjögren's syndrome is an autoimmune disease linked to saliva gland infection of coxsackievirus B4.
Increasing evidence indicates
POTS is autoimmune, at least in some subsets.
I cannot see any major role that connective tissue disorders are playing in the above diseases.
However, if you have Ehlers-Danlos syndrome (EDS), then
one study found
ALL diseases were significantly more common in EDS patients.
So if you have EDS, it seems you are more prone to getting diseases of all sorts.
The reason EDS patients are more susceptible to all diseases may not be directly due to connective tissue dysfunction, but might conceivably involve the
immune weakness found in EDS.
People like Paul Ewald think that nearly all chronic diseases and cancers will turn out to be caused by persistent infectious pathogens in the body. And it is certainly a fact that most diseases have been linked to persistent infections.
So if it is true that pathogens are the hidden cause of most diseases, then the immune weakness of EDS patients may explain why they are more prone to chronic disease.