Coeliac disease appears to be multifactorial, both in that more than one genetic factor can cause the disease and in that more than one factor is necessary for the disease to manifest in a person. Almost all people (95%) with coeliac disease have either the variant HLA-DQ2 allele or (less commonly) the HLA-DQ8 allele. However, about 20–30% of people without coeliac disease have also inherited either of these alleles
Severe coeliac disease leads to the characteristic symptoms of pale, loose, and greasy stool (steatorrhoea) and weight loss or failure to gain weight (in young children). People with milder coeliac disease may have symptoms that are much more subtle and occur in organs other than the bowel itself. It is also possible to have coeliac disease without any symptoms whatsoever. Many adults with subtle disease only have fatigue or anaemia.
Combining findings into a prediction rule to guide use of endoscopic biopsy reported a sensitivity of 100% (it would identify all the cases) in a population of subjects with a high index of suspicion for coeliac disease, with a concomitant specificity of 61% (a false positive rate of 39%). The prediction rule recommends that people with high-risk symptoms or positive serology should undergo endoscopic biopsy of the second part of the duodenum. The study defined high-risk symptoms as weight loss, anaemia (haemoglobin less than 120 g/L in females or less than 130 g/L in males), or diarrhoea (more than three loose stools per day).
More than 330,000 Canadians are believed to be affected by celiac disease with only approximately 110,000 diagnosed. Each year, families affected by celiac disease spend $150 million to obtain gluten-free foodstuffs; the primary therapeutic option for the disease.