Celiac disease or gluten-sensitive enteropathy is an immune-
mediated disorder that primarily affects the gastrointestinal tract 
and is characterized by chronic inflammation of the small intestine 
mucosa, which may result in atrophy of intestinal villi, malabsorption 
and a variety of clinical manifestations. It is caused by a 
pathological intolerance to gliadin, the alcohol-soluble fraction of 
gluten in wheat, rye and barley. Celiac disease manifests at any age 
with a peak onset in early childhood. Recent studies now suggest that 
its prevalence is in the range of 0.5 to 1.0% of the U.S. population 
with certain populations having an increased prevalence of celiac 
disease. Celiac disease is also associated with selective IgA 
deficiency and autoimmune disorders.  The US incidence rate is 1:130, 
which is similar to European countries.

Diagnosis of celiac disease is based on a combination of clinical 
symptoms and the following factors:
   IgA and/or IgG antibodies to tissue transglutaminase (TTG)
   IgA and/or IgG antibodies to deamidated gliadin
   Endomysial IgA and/or IgG antibodies
   Human leukocyte antigen (HLA)-DQ2 or DQ8 genotypes
   Biopsy of the small intestine (demonstrating flat mucosa)
   Or a patient's satisfactory response to a gluten-free diet (GFD).

IgA deficiency is more common in the celiac disease (2-3%) versus the 
average population (0.1-0.2%).  Therefore, it is recommended that IgG 
antibodies to deamidated gliadin be determined if there is total IgA 
deficiency. Current guidelines indicate that DGP IgG may be useful in
children less than 2 years old.  Except for children less than 2 years
old, deamidated gliadin IgG generally has lower sensitivity and
specificity than deamidated gliadin IgA in patients without total IgA
deficiency.

References:
1. The National Institutes of Health (NIH) Consensus Development
   Conference on Celiac Disease, NIH Consensus Development Conference
   Statement, June 28-30, 2004. 
2. van der Windt, et al. Diagnostic Testing for Celiac Disease Among
   Patients with Abdominal Symptoms: a Systematic Review. JAMA May
   2010, 303(17);1738-46. 
3. G. Holmes, C. Catassi, A. Fasano. Fast Facts: Celiac Disease. 2nd
   Edition; August 2009, 57-63. 
4. Rashtak S., Ettore M., Homberger H., Murray J. Comparative
   Usefulness of Deamidated Gliadin Antibodies in the Diagnosis of
   Celiac Disease. Clin Gastroenterol Hepatol April 2008, 6(4); 426-
32. 
5. Green, P.H., Jones. R. Celiac Disease: A Hidden Epidemic. 2006,
   45-48. 
6. Van Meensel B, Hiele M, Hoffman I, et al. 2004. Diagnostic accuracy
   of ten second-generation (human) tissue transglutaminase antibody
   assays in celiac disease. Clin Chem. 50: 2125-35.