Anti-Tissue Transglutaminase IgG

Celiac disease is characterized by chronic inflammation of
the intestinal mucosa and flattening of the epithelium
(positive villous atrophy). The origin of the celiac disease is
the intolerance to gluten, the protein of wheat, rye and
barley. The main symptoms are diarrhea, gastrointestinal
problems, anemia, fatigue, psychiatric problems and other
diverse side effects. In some cases patients may be
asymptomatic.
Clinical and mucosal recovery after institution of a gluten
free diet is objective evidence that the enteropathy is
gluten induced.
Diagnosis of celiac disease is confirmed by abnormal
findings on the small bowel biopsy and later verified by the
clinical response to a gluten-free diet, i.e. the avoidance of
wheat, barley, rye, oats and triticale.
Left untreated patients suffering from celiac disease have
an increased risk of lymphoma or gastrointestinal
neoplasm. Furthermore, even if clinically silent,
longstanding untreated celiac disease predisposes for
other autoimmune diseases, like Diabetes mellitus,
rheumatoid diseases, autoimmune hepatitis or thyroiditis.
The European Society for Pediatric Gastroenterology and
Nutrition (ESPGAN) draw the guidelines for the celiac
disease diagnosis, including: a) an initial positive gut
biopsy, b) 6 months on a gluten-free diet, c) a negative
second gut biopsy, d) a gluten challenge for 6 months e) a
positive third gut biopsy.
Recently, the development of serum tests for three
different antibodies of the IgA isotype made it possible to
modify these guidelines for celiac disease. These revised
ESPGAN criteria include: a) a single positive gut biopsy
and b) the demonstration of at least two of the three IgA
class antibodies against gliadin, endomysium or
transglutaminase.
The enzyme tissue Transglutaminase (tTG) has been
reported to be the main, if not sole, target for endomysial
antibodies. These antibodies fall once a gluten-free diet
has begun, thus facilitating monitoring of dietary compli- ance. Anti-tTG IgG are a highly sensitive marker for celiac
disease with 95-100%, and have a specificity of 90 to 97%.
SInce two years the human tTG antigen has been
produced by recombinant technology. This new antigen
allows certain advantages compared with the traditional
guinea pig liver antigen.
There is a percentage of patients that don’t produce any
IgA and probably they represent the single largest
contributor to a false negative serological result in biopsy
confirmed celiac patients. To correctly evaluate this group
of patients, many laboratories perform IgG determinations
of several samples tested for the presence of antibodies
against celiac disease. Most IgA deficient celiac patients
are found to be positive for IgG class, reticulin and gliadin.
Several studies on the use of IgG against t-TG to find
patients not producing IgA demonstrated that test
sensitivity was increased from 91.5% for IgA antibody
alone to 98.5% when both IgA and IgG results were
considered.