What are the gluten-dependent diseases?
Gluten-dependent diseases primarily include coeliac disease, which is an autoimmune disease. Other gluten-dependent autoimmune diseases include dermatitis herpetiformis (a.k.a. Duhring’s disease) and the cerebellar form of coeliac disease, gluten-dependent ataxia.
The second group of conditions that depend primarily on wheat proteins are allergic diseases. In this group, we distinguish between the most common wheat food allergy and baker’s inhalation allergy. Contact urticaria or wheat-dependent post-exercise anaphylaxis must also be added to the list.
In the case of allergies, unlike coeliac disease, gluten is not always the causative agent. Admittedly, 80% of allergic symptoms are induced by this ingredient. However, in some patients, other proteins contained in wheat flour, such as albumin or globulins, i.e. water-soluble proteins, may be the cause. Recently, we have further distinguished a third group of gluten-dependent diseases, the so-called non-coeliac gluten hypersensitivity, and in fact we now emphasise that it is rather a wheat hypersensitivity. The pathomechanism of this disease is not yet fully understood.
What do we know about gluten?
Gluten is the conventional and common name for the mixture of proteins found in cereal grains. These are proteins that are not soluble in water. Gluten that comes from wheat is gliadin, from barley is hordein, and from rye is secalin.
Myths about coeliac disease
When it comes to celiac disease, there are countless myths. The main ones are:
– Coeliac disease is a childhood disease – we often hear this statement, but it is not true. Both children and adults suffer from coeliac disease. Furthermore, approximately 60% of newly diagnosed cases are now in adults, including those over 60 years of age.
- It is also a myth to say that there is no coeliac disease without diarrhoea. Presently, non-classical forms predominate, often with symptoms from outside the gastrointestinal tract. In patients from the gastrointestinal side, in addition to diarrhoea, there may be constipation, abdominal pain or flatulence. On the other hand, symptoms from outside the gastrointestinal tract include anaemia, growth disorders, joint pain, osteoporosis/osteopenia, skin lesions, excessive fatigue, hypersensitivity, headaches, a tendency to depression, delayed sexual maturation in children, and infertility in adults.
- A patient with coeliac disease is characterised by weight deficiency. This is another myth. In Poland, only one-third of children with coeliac disease are underweight, while 10% are found to be overweight or obese. Among adults, the percentage of overweight or obese patients is even higher.
- Some people believe that once the symptoms of coeliac disease have subsided, a gluten-free diet can be discontinued. This is utterly wrong. The only treatment for celiac disease is a restrictive gluten-free diet that must be followed for life.
Food allergy versus coeliac disease – illnesses with many faces
The symptoms of both allergy and coeliac disease are highly variable, although they can be similar. Gastrointestinal symptoms such as diarrhoea, abdominal pain, flatulence, nausea, vomiting, reduced appetite or constipation are observed in both coeliac disease and food allergy.
Itchy skin lesions are slightly more common in allergy. However, they can also be present in coeliac disease (e.g. in the cutaneous form of coeliac disease, i.e. Duhring’s disease). Anaemia may be present in both diseases. It may be more common in coeliac disease, but this does not mean that it is not present in allergy. A large group of symptoms are related to disposition, difficulty concentrating, a low mood or chronic fatigue. These can occur in both diseases. The main differentiating symptoms between coeliac disease and allergy are respiratory symptoms (dyspnoea) and anaphylactic shock, which only occur in allergy.
Does coeliac disease co-occur with allergies?
Coeliac disease often co-occurs with many autoimmune diseases. But the question also arises, can it occur with allergies? Our research shows that 13% of patients with coeliac disease claim to have an allergy, primarily atopic dermatitis (AD).[1] Studies show that in children with AD, coeliac disease is four times more common than in the rest of the population. However, it should be emphasised that some skin lesions that are initially diagnosed as AD can be a symptom of coeliac disease. This is evidenced by the case of our patient who was treated for AD for almost seven years. However, it was only when the tests for coeliac disease were performed that it was coeliac disease. The introduction of a gluten-free diet resulted in the disappearance of the lesions.
How do we diagnose allergy and how coeliac disease?
Tools for the diagnosis of IgE-dependent allergy are very well developed. We have tests to assess the concentration of specific serum IgE antibodies to allergen extracts or components (molecular component diagnostics), as well as spot skin tests. For IgE-independent allergy, we currently do not have serological tests. Patch tests are useful in diagnosis.
The elimination of the allergen from the diet and a challenge test are considered the gold standard for the diagnosis of food allergy. These are carried out after approximately 6-12 months of an elimination diet. And this is where the problems begin. Why? The elimination of gluten from the diet prevents us from diagnosing celiac disease. Therefore, before we take gluten out of the diet, it is important to check whether the patient has celiac disease. The diagnosis of coeliac disease is based on highly sensitive and specific serological tests.
Standards in the diagnosis of coeliac disease
From 2020, new standards for the diagnosis of this disease in children and adolescents are in use [2]. According to the guidelines of the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN recommendations), a determination of antibodies to tissue transglutaminase class IgA (TTG-IgA) and a determination of total IgA should be performed first. The determination of total IgA is important because, on average, one in ten patients with coeliac disease is deficient in these antibodies. If a patient is deficient in total IgA, we then perform tests to assess the concentration of antibodies in the IgG class (TTG-IgG). In children whose TTG-IgA concentration is more than ten times the upper limit of normal for a given test, we do not need to perform a small bowel biopsy and genetic testing to make a diagnosis. A high concentration of antibodies to TTG-IgA is sufficient to diagnose coeliac disease in a paediatric patient.
In adults, the gold standard for the diagnosis of coeliac disease is still a small bowel biopsy and evaluation of lesions. However, it should be stressed that lesions considered typical of coeliac disease are also found in other diseases, including food allergy. Therefore, serological testing for specific antibodies is also recommended in adults before biopsy.
Diagnosis of coeliac disease in Poland is still a problem
Despite established guidelines and having sensitive and specific serological tests, the diagnosis of coeliac disease in Poland is still very challenging, especially in adults. The survey we conducted among more than 900 patients shows that, on average, coeliac disease is diagnosed in our country more than 7 years after the first symptoms appear. In children, the diagnosis is made sooner, after about three years. Adults, on the other hand, wait more than 9 years from the first symptoms to be diagnosed [1].
Summary:
- The symptoms of coeliac disease and wheat allergy are varied with a similar nature
- The basis for differential diagnosis (coeliac disease vs. allergy) is a serological test for specific antibodies to coeliac disease
- The most sensitive and specific antibodies for diagnosing coeliac disease are antibodies to tissue transglutaminase, in the IgA class.
- Evaluation of their concentration must be performed on a normal diet (without gluten elimination).
- The gold standard for the diagnosis of food allergy is the elimination and allergen challenge test.
