Coeliac disease is an autoimmune disease which, due to its ability to masquerade itself, is often underdiagnosed.
It affects around 1 in 100 people and increased awareness among clinicians and patients has improved disease detection.
Women are affected more than men and there is an increased risk in those with Down's syndrome, Turner's syndrome and type-1 diabetes mellitus.
In addition, patients with coeliac disease are more likely to have other autoimmune diseases.
Coeliac disease does not occur in those without alleles that code for HLA-DQ2 or HLA-DQ8 proteins.
The twin concordance rate, however, is less than 50 per cent and the presence of HLA proteins does not have a 100 per cent positive predictive value for coeliac disease suggesting there are other aetiological factors involved.
Studies have shown the protective nature of breast feeding. Premature exposure to gluten before four months of age confers an increased risk of developing coeliac disease.
2. Signs and symptoms
Coeliac disease manifests when the gut is exposed to gluten, a protein found in wheat, rye and barley. Gluten is poorly digested and contains gliadin, which is the main dietary culprit in coeliac disease.
In susceptible people, exposure to gliadin promotes an inflammatory reaction involving many components of the immune system. The consequences of this are variable and may be serious.
Classic symptoms of coeliac disease include failure to thrive, diarrhoea and abdominal pain or bloating. However, vague and non-specific symptoms may also manifest such as fatigue, weight loss, irritability, constipation and vomiting.
Patients with evidence of malabsorption, such as anaemia or hypoalbuminaemia, dermatitis herpetiformis, osteoporosis or short stature may eventually be diagnosed with coeliac disease.
Concern about a diagnosis of coeliac disease should prompt serological testing in the first instance, which is often performed in primary care.
NICE suggests that testing may also be offered in the presence of Addison's disease, amenorrhoea, mouth ulcers, autoimmune liver disease, autoimmune myocarditis, chronic thrombocytopenia purpura, depression, bipolar disease, epilepsy, low-trauma fracture, Down's syndrome, Turner's syndrome, lymphoma, rickets/osteomalacia, unexplained persistent constipation, unexplained raised LFTs, recurrent miscarriage and infertility, sarcoid, Sjogren's syndrome and unexplained alopecia.
IgA antibodies are the most sensitive antibody class when screening for coeliac disease. IgA deficiency is not uncommon in the general population (1 in 400), and is 10 times more prevalent among coeliac patients. Those with IgA deficiency require testing with IgG rather than IgA antibodies.
A number of different serological tests are available including anti-tissue transglutaminase (TGG), anti-gliadin, anti-reticulin and anti-endomysial antibodies. Anti-TTG antibodies should be requested first line as the test offers a sensitivity in excess of 90 per cent.
In addition, titres correlate to disease severity. Anti-endomysial antibodies should be requested with an equivocal anti-TTG antibody result.
HLA alleles may be tested for, although this is not recommended in primary care. Those without alleles coding for HLA-DQ2 or HLA-DQ8 are highly unlikely to have the disease with a negative predictive value of approximately 100 per cent.
The gold standard for diagnosing coeliac disease is duodenal biopsy. This should be performed in patients where coeliac disease is clinically suspected but with negative serologuy, or to confirm positive serology.
Serology and biopsies can be falsely reassuring if a patient is adhering to a gluten-free diet and patients will be required to have a gluten diet for at least six weeks prior to testing.
FBC, ferritin, B12 and folate are also useful tests. LFTs may be abnormal and testing for other autoimmune diseases such as thyroid disease is often performed.
The treatment of coeliac disease is essentially adherence to a gluten-free diet. Many gluten-free products are available on an FP10 prescription.
Malabsorption, particularly of the B vitamins, may occur with this diet although one would need to exclude pernicious anaemia. Many physicians advise vitamin and calcium supplements to their patients, and referral to a dietician is often required. Some centres offer recombinant enzyme therapy to eliminate gliadin from the bowel.
Some patients fail to improve despite treatment. The most common cause for this is poor adherence to a gluten-free diet. Misdiagnosis may also explain poor response to treatment and there are other causes of villous atrophy which may be mistaken for coeliac disease on biopsy specimens, including giardia and immune deficiency.
Many patients may find information from organisations such as Coeliac UK highly informative in managing their condition.
Except for malabsorption, serious consequences of coeliac disease include adenocarcinoma and T-cell lymphoma of the bowel, hence the need for regular surveillance.
There is data that suggests that a gluten-free diet reduces risk of malignancy to that of the greater population. Other reported cancers include pancreatic and hepatobiliary.
Coeliac disease should certainly be considered where the diagnosis is otherwise unclear.
- Dr Thakkar is a GP in Wooburn Green, Buckinghamshire
- NICE. Recognition and assessment of coeliac disease. CG86. London, NICE, 2009. Available from http://guidance.nice.org.uk/CG86
- Coeliac UK www.coeliac.org.uk
- Green P and Cellier C. Celiac disease. N Engl J Med 2007; 357: 1,731-43