Coeliac disease

Alternative names

Non-tropical sprue, gluten-induced enteropathy, coeliac sprue

Definition

This is a chronic disorder caused by an intolerance to gluten, which is a protein found in wheat and wheat products.

Coeliac disease leads to damage of the small intestinal lining. This can result in impairment in absorption of fats and other nutrients into the bloodstream.

Causes

Gluten and a substance related to gluten called gliadin are heavy proteins. They are found particularly in wheat and rye and to a lesser extent in barley and oats. These proteins are harmful to people who have coeliac disease. The exact mechanism for this effect is not known, but two alternative theories have been proposed to explain how this harm comes about: the toxic theory and the immune theory.

According to the toxic theory, people with coeliac disease lack a particular enzyme which is normally found on the mucous membranes (mucosa) which line the small intestine. The function of this enzyme is to break gluten and gliadin down into smaller particles which are then able to pass through the wall of the intestine into the bloodstream. So, according to this theory, if a person with coeliac disease eats food containing gluten and gliadin, the lack of this enzyme will lead to an accumulation of gluten and gliadin on the mucous membranes of the small intestine. It is suggested that this accumulated gluten and gliadin has a toxic effect on the mucosa.

Alternatively, the immune theory claims that gluten or the breakdown products of gluten (metabolites) start an immunological reaction in the mucosa of the small intestine which causes structural abnormalities to develop in the mucosa. Evidence for this is not clear.

Who gets it?

There are no accurate estimates of the incidence of coeliac disease in our local population. The disease tends to affect individuals of European descent. Estimated incidence in the UK is 1:100.

The disease is more common in women, with a female: male ratio of 2:1.

The disease affects all age groups, including infants and children.

The severity of the disease varies widely between individuals. Surprisingly, it has been found that some people who have the small intestinal abnormalities characteristic of the disease do not suffer any symptoms at all.

There appears to be a hereditary component to the disease since the incidence among siblings is higher than in the general population. However, the cause of Coeliac disease is complex and multifactorial. It is not regarded as purely an inherited disease.

People with coeliac disease have a higher frequency of what are called serum histocompatibility antigens – HLA antigens. The HLA system is part of the immune system, and is a series of four gene families, which provide the coding for a particular protein present on the surface of cells. When two individuals have identical HLA types, they are said to be histocompatible. HLA-DQ2 has been found in 90% of people with coeliac disease as compared with 20 to 25% in the normal population. This indicates the nature of the hereditary component of the disease.

Symptoms and signs

Most people with coeliac disease will have symptoms of malabsorption of food such as weight loss and diarrhoea. They may also show abnormal results on laboratory tests that measure how effectively the small intestine absorbs food.

Some people may suffer from abdominal discomfort and bloating as well. Other unusual manifestations include skin lesions and neurological disturbances such as difficulty walking and imbalance.

If the malabsorption is sufficiently severe anaemia may develop in both adults and children. This may be due to malabsorption of essential vitamins such as folatic acid and vitamin B12, as well as iron.

Diagnosis

People with Coeliac disease may complain of the symptoms mentioned above or show signs that suggest the diagnosis.

Laboratory tests will aid in confirming the diagnosis. Laboratory studies may show characteristic types of anaemia, as described above.

The blood may be low in albumin (a form of protein). Tests of intestinal absorption are often abnormal and there may be an abnormal amount of fat in the stool.

Certain antibody blood tests may aid in the diagnosis. An antibody known as anti-endomysial antibody is found in 95% of patients with coeliac disease and can be used to screen for the disease in relatives of affected patients or in patients suspected of having the disease.

To confirm the diagnosis of coeliac disease a biopsy must be obtained. This entails a small piece of the small intestine being snipped off under guidance through an endoscopic tube (a tube that allows the doctor to see inside the body), and examined under a microscope. In patients with coeliac disease the surface of the small intestine shows several highly suggestive abnormalities. Normally, the internal surface of the small intestine is covered in tiny finger-like projections called villi. These villi greatly increase the surface area of the bowel, thereby increasing the rate at which digested food particles can be absorbed into the bloodstream.

When a person has coeliac disease, these villi are destroyed so that the surface of the bowel looks flat when viewed under magnification. It is this loss of villi called villous atrophy that leads to the impairment of nutrient absorption from the small intestine.

The symptoms of the disease should improve once the patient has been placed on a gluten-free diet, and this, too, should aid in the diagnosis of the disease. A definite diagnosis of coeliac disease can be made if there is improvement of villous atrophy on repeat biopsy performed when the patient is on a gluten-free diet.

Treatment

The treatment consists of complete avoidance of gluten in the diet.

In moderate to severe cases of the disease, supplementary vitamins, minerals and iron are given, according to the degree of deficiency. In mild cases, such supplementation is usually unnecessary.

Gluten is widely used in foods, so patients need to consult a dietician to obtain a detailed list of foods to avoid.

Outcome

Avoiding gluten usually allows the person to live a normal life. Very rarely patients do not respond to a gluten-free diet alone and may require other treatments such as corticosteroids.

In severe cases, however, even after eliminating gluten from the diet, there is some mortality from the disease, mainly among adults. An important cause of death is the development of intestinal lymphoma. A strict gluten-free diet has been shown to protect against this malignancy.

When to see your doctor

If you or any member of your family develops symptoms similar to those listed above after eating wheat products, then see your doctor.

This is particularly true if an immediate relative suffers from the disease.

Reviewed by Dr G Watermeyer MBChB FCP(SA), Cert Gastoenterology(SA), Consultant GIT Clinic Groote Schuur Hospital