Celiac disease (CD) is an inflammatory disease that affects the small intestine. It is caused by the consumption of gluten in genetically predisposed people. Gluten is a protein found in various grains, including rye, wheat, and barley, as well as in products that contain it. Chronic inflammation of the small intestine changes the structure of the intestinal lining and leads to poor absorption of nutrients.
The prevalence of CD is estimated at 1% among the global population. The disease is mainly seen in people of Caucasian descent and affects about twice as many women as men. Some people are at greater risk of developing CD. This is particularly the case for first-degree relatives (mother, father, brother, sister, child) and people with another disease such as Down syndrome or type 1 diabetes.
The development of CD requires the ingestion of gluten as well as a genetic predisposition . In people with CD, ingestion of gluten triggers the immune system to produce antibodies. These antibodies damage the inner lining of the small intestine by causing atrophy (shortening) of the villi, the tiny hairs responsible for absorbing nutrients. The absence of villi reduces the absorption surface of the intestine and leads to poor absorption of nutrients. Because CD is an inherited disease, people with it must carry certain genes, HLA-DQ2 and / or HLA-DQ8. However, people who carry these genes do not always develop the disease.
Symptoms of CD can appear at any age and can vary widely. The severity of symptoms seen depends on the proportion of the small intestine affected by the disease. In children, symptoms usually include abdominal bloating, stunted growth, and diarrhea. There may also be other symptoms such as anorexia, vomiting, and anemia. In adults, many people are asymptomatic and have no digestive symptoms. Otherwise, symptoms can include diarrhea, undernutrition, and weight loss. There may also be anemia, osteoporosis, abdominal pain, abdominal bloating and reduced fertility. In addition, about 10% of people with CD have dermatitis herpetiformis, a painful rash.
The diagnosis of CD is based on the presence of the above symptoms, blood tests, biopsies of the small intestine and response to a gluten-free diet. Doctors may also use genetic tests to make their diagnosis.
Blood tests are used to measure the antibodies against gluten. They should be performed in individuals who consume gluten . The dosage of the antibodies is proportional to the degree of villous atrophy. If the tests are positive, the individual should undergo an intestinal biopsy to make the diagnosis. If the tests are negative, CD is unlikely.
Small intestine biopsy
A small intestine biopsy involves removing a small piece of tissue from the intestinal lining in order to observe its structure under a microscope. It should be performed in individuals whose diet contains gluten. In the majority of people with CD, a biopsy of the intestinal lining shows villous atrophy. However, the absence of villi is not specific to CD, which is why blood tests are also needed to make the diagnosis.
Response to a gluten-free diet
A positive response to a gluten-free diet also supports the diagnosis of CD. A response is positive if there is resolution of symptoms, a decrease in the levels of antibodies against gluten and a normalization of the surface of the small intestine following the initiation of a gluten-free diet.
In some cases, the diagnosis may also include genetic tests, especially when the blood tests and the biopsy do not match. Genetic testing can be used to find out if a person has genes associated with CD. If the genes are absent, CD is excluded. However, their presence is not diagnostic of CD, as carriers may never develop the disease.
CD affects the absorption of nutrients in the small intestine. The severity of malabsorption and its consequences depend on the extent of the villous atrophy. The larger the area of the intestine affected by the disease, the greater the malabsorption and its consequences. The nature of the malabsorbed nutrients can also vary depending on the portion affected by the disease. For example, if the affected portion is the duodenum and the proximal jejunum, the malabsorption particularly concerns iron, folate and calcium which are mainly absorbed from this height of the intestine. The consequences include macrocytic anemia and loss of bone mass. If the entire small intestine is affected, then all macronutrients (carbohydrates, fats, and proteins) and micronutrients (vitamins and minerals) may be poorly absorbed. Carbohydrate malabsorption can cause diarrhea, gas, and bloating. Protein malabsorption can cause edema and loss of muscle mass. There may also be signs of vitamin and mineral deficiencies such as iron deficiency anemia and loss of bone mass. Many adults with CD have low bone mass (osteopenia, osteoporosis) and are at greater risk for fractures than the general population.
Currently, the only treatment for CD is to follow agluten free diet for life. Complete exclusion of gluten from the diet is required, as even small amounts can cause symptoms. The gluten-free diet excludes rye, oats (pure, uncontaminated oats are allowed), wheat (including kamut and spelled), barley and triticale (a hybrid between rye and wheat) . Due to the ubiquity of gluten in the North American diet, such a diet can be complex to follow. It is therefore recommended to consult a dietitian in order to carry out a nutritional assessment, to receive education on the gluten-free diet and to ensure follow-up. In more severe forms of the disease, doctors may also prescribe vitamin and mineral supplements. It is important to remember that the diagnosis of CD must be made before the gluten-free diet is started.
The gluten-free diet helps with symptoms, antibody levels and villous atrophy. Usually, symptom improvement occurs about 2 weeks after starting the gluten-free diet. Then, blood tests show a decrease in antibody levels between 6 to 12 months after starting the diet. Finally, a few months to two years after removing gluten from the diet, the small intestine usually returns to its usual structure (presence of villi) and resumes its normal absorption functions.
In the absence of improvements following the initiation of the diet, the diagnosis should be rechecked and compliance with the diet verified. If the diagnosis is correct and the diet is followed, other causes such as cancer of the small intestine, lactose or fructose intolerance or other food allergies should be ruled out. It is also possible that the CD is returned to the refractory stage. In this case, individuals continue to have gastrointestinal symptoms and present with villous atrophy despite adherence to a gluten-free diet. For refractory CD, doctors may prescribe corticosteroids to control symptoms.
Individuals with undiagnosed CD and those with poor adherence to the gluten-free diet have higher mortality than the general population. However, fatal outcomes are rare and the majority of people live normally on a gluten-free diet. People with CD are also at greater risk of developing certain cancers of the digestive tract, including lymphoma of the small intestine. Adherence to a gluten-free diet significantly reduces the risk of cancer.
The only treatment available for CD today is to have a gluten-free diet for life. However, this diet can be difficult to follow and some people continue to have symptoms despite adherence to it. There is therefore a need for the development of non-food treatments. Different mechanisms involved in the functioning of CD have been identified during clinical trials as potential avenues for developing non-food treatments. Potential treatments include enzymatic breakdown of gluten, sequestration of gliadin (the toxic moiety of gluten), protection of gut cells against gliadin with a probiotic, gluten tolerance with a vaccine, and treatments targeting immune cells. At this time, there are no approved non-food treatments and more studies are needed to develop an alternative treatment for CD.
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