Gastrointestinal
Gastrointestinal symptoms may include any of the following: abdominal pain, bloating, bowel habit abnormalities (either diarrhea or constipation), nausea, aerophagia, flatulence, gastroesophageal reflux disease, and aphthous stomatitis. Extraintestinal
NCGS can cause a wide range of extraintestinal symptoms, which can be the only manifestation of NCGS in absence of gastrointestinal symptoms. These include any of the following: headache, migraine, "foggy mind", fatigue, fibromyalgia, joint and muscle pain, leg or arm numbness, tingling of the extremities, dermatitis (eczema or skin rash), atopic disorders such as asthma, rhinitis, other allergies, depression, anxiety, iron-deficiency anemia, folate deficiency, or autoimmune diseases. NCGS is also linked to a wide spectrum of neurological and psychiatric disorders, including  ataxia, schizophrenia, epilepsy, peripheral neuropathy, encephalopathy, vascular dementia, eating disorders, autism, attention deficit hyperactivity disorder (ADHD), hallucinations (so-called "gluten psychosis"),  and various movement disorders (restless legs syndrome, chorea, parkinsonism, Tourette syndrome, palatal tremor,  myoclonus, dystonia, opsoclonus myoclonus syndrome, paroxysms, dyskinesia, myorhythmia, myokymia).Above 20% of people with NCGS have IgE-mediated allergy to one or more inhalants, foods, or metals, among which most common are mites, graminaceae, parietaria, cat or dog hair, shellfish, and nickel. Approximately 35% of patients suffer other food intolerances, mainly lactose intolerance. Causes
The pathogenesis of NCGS is not yet well understood, but the activation of the innate immune system, the direct cytotoxic effects of gluten, and probably the cytotoxicity of other wheat molecules are implicated. Besides gluten, other components in wheat, rye, barley, and their derivatives, including amylasetrypsin inhibitors (ATIs) and FODMAPs, may  cause symptoms.
More complete is an open system, namely, in its simplest form,

  
    
      
        R
        
          
            →
            
          
        
        A
        
          
            →
            
               
               
              p
              (
              S
              )
               
               
            
          
        
        B
        
          
            →
            
               
               
              q
               
               
            
          
        
        ,
      
    
    {\displaystyle R{\xrightarrow {}}A{\xrightarrow {\ \ p(S)\ \ }}B{\xrightarrow {\ \ q\ \ }},}
  
where R stands for the rate of production of A, p(S) is the activation rate coefficient explicitly expressing its dependence on the stimulus intensity S and q represents the rate coefficient of removal from the state B.