New Serology for Celiac Disease?

A recent study (RS Choung et al. Gastroenterol 156: 582-91) showed that synthetic neoepitopes of the transglutaminase-deamidated gliadin complex are better noninvasive biomarkers for detecting celiac disease and for monitoring mucosal healing.

Link to Graphical Abstract and Abstract: Synthetic Neoepitopes of the Transglutaminase–Deamidated Gliadin Complex as Biomarkers for Diagnosing and Monitoring Celiac Disease

The authors studied the serum samples from 90 patients with Celiac disease (CD) and from 79 healthy controls and developed a fluorescent peptide microarray platform  Then, the authors validated their findings in 82 patients with newly diagnosed CD and 217 controls.

Key findings:

  • 7% of patients with treated (with gluten free diet [GFD]) and healed CD had positive TTG-IgA and 27% of patients treated but unhealed CD mucosa had positive TTG IgA
  • With the synthetic neoepitopes, CD was identified with 99% sensitivity and 100% specificity.  The assay identified patients with CD with healed mucosa with an 84% sensitivity and 95% specificity.

My take: More precise noninvasive markers like these should help identify individuals with celiac disease and those who have responded (or not) to the recommended gluten free diet.

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Unrelated but important —NPR reports on another large study showing that MMR does not cause autism -Link: A Large Study Provides More Evidence That MMR Vaccines Don’t Cause Autism 

Related blog post: “Too many vaccines and autism” debunked

Link to full text of study from Annals of Internal Medicine: Measles, Mumps, Rubella Vaccination and AutismA Nationwide Cohort Study

“To biopsy or not to biopsy” –that is the question (for Celiac disease)

First off -thanks to Ben Gold for the following reference and the blog title as well.

  • CM Trovato et al. Am J Gastroenterol 2015; 110: 1485-89.

In this retrospective study (alluded to in a previous post:Celiac Update September 2015 | gutsandgrowth), the researchers examined whether “biopsy-sparing” protocols for symptomatic children with high titers of serum anti-transglutaminase (anti-TTG) antibody levels (>10 times upper limit of normal [ULN]) would be suitable for asymptomatic patients.

Background: In 2012, the European Society for Pediatric Gastroenterology Hepatology and Nutrition (ESPGHAN) published guidelines that it is possible to omit endoscopic biopsies for celiac disease if patients older than 2 years of age had high anti-TTG titers (>10 times ULN), positivity for EMA, compatible HLA DQ2 or HLA DQ8 and were symptomatic.

Findings:

  • Among 196 patients, the 40 who were asymptomatic had severe Marsh lesions (3a, 3b, or 3c) in 92% compared with 91% of 156 who were symptomatic. In both groups, the remaining patients had either Marsh 1 or 2 lesions.
  • 94.4% of patients had improved serology during followup along with symptomatic improvement (in those with symptoms)

Bottomline:  Whether symptomatic or not, those with high antiTTG titers who meet all of the other ESPGHAN criteria have a very high probability of celiac disease.

Briefly noted: K Marild et al. Am J Gastroenterol 2015; 110: 1475-84. This study, based on a large prospective Norwegian cohort (72,921 children) that frequent infections (>10) in the first 18 months of life increased the risk of celiac disease with an adjusted odds ratio of 1.32 (highest infection quartile compared to lowest infection quartile).  However, alternative explanations, including surveillance bias and reverse causation, cannot be excluded.

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How Likely is Celiac Disease if My TTG Test Is Only a Little Bit Abnormal?

A terrific celiac serology study (Gidrewicz D, et al.Am J Gastroenterol 2015; -advanced online publication doi: 10.1038/ajg.2015.87) helps answer questions about the utility of serology in making diagnostic decisions. (Thanks to corresponding author J Decker Butzner for sharing reference.)

Using consecutive samples in a laboratory database with 17,505 patients, the authors retrospectively examined the performance of the tissue transglutaminase (TTG), endomysial antibody (EMA) tests and the ESPGHAN celiac guidelines for nonbiopsy diagnosis of celiac disease.  Among this large cohort, 775 with positive TTG and 574 with a negative TTG were biopsied.

Key findings:

  • If the TTG >10-fold the upper limit of normal (ULN) along with a positive EMA and symptoms were present, 98.2% had biopsies consistent with celiac disease.
  • If the TTG was 3-10-fold-ULN along with positive EMA, then 75.7% had biopsies consistent with celiac disease.  The histology of celiac disease (CD) was present in only 40% of the TTG 3-10-fold ULN if EMA was negative.
  • If the TTG was 1-3-fold-ULN along with positive EMA, 52.2% had CD-positive histology, whereas CD-positive histology was evident in only 13.3% of TTG 1-3-ULN if EMA was negative.
  • IgA deficiency is common in CD (“1in 60 vs 1 in 700” in general population)

Implications & Take-home points:

  • The researchers note that the positive predictive value of TTG drops when the prevalence of CD in the testing population is lower.  Thus, in their population and most clinical practice where the prevalence is below 35-40%, the PPV of the TTG-based tests drops to <80%.
  • While TTG-based tests have high specificity, there are multiple medical conditions that can cause a false positive (additional reference below), including autoimmune diseases like diabetes mellitus, inflammatory bowel diseases as well as infections, and liver disorders.
  • Asymptomatic patients with low TTG titers and negative EMA may benefit from following celiac serology rather than proceeding immediately to intestinal biopsy.
  • Using ESPGHAN nonbiopsy criteria (symptomatic child, TTG ≥10 ULN, positive EMA, positive HLA typing), there were four patients whose initial biopsies were not consistent with CD.  Thus these criteria identified 98.2% accurately who did not need an intestinal biopsy.  One of these four developed CD subsequently.  To achieve 100% PPV for non biopsy, the authors note that one would need an EMA titer ≥1:80.
  • Study limitations: retrospective study, lack of standardization between TTG assays

Bottomline: EMA improves the PPV of TTG testing, especially when low titer elevations are noted.  TTG alone is a highly sensitive test “with a 99.4% negative predictive value” in this study.

Related study: “Serum Anti-Tissue Transglutaminase Antibodies Detected during Febrile Illness May Not be Produced by the Intestinal Mucosa” J Pediatr 2015; 166: 761-3.  This case report describes two children with abnormal TTG (one more than 20-fold ULN)) both were EMA-negative. No mucosal anti-TTG was identified using two immunoassays.

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Elevated Celiac Serology Associated with Reduced Infant Birth Weights

Using a population-based study of 7046 singleton pregnancies (from the Netherlands), the authors of a recent study have shown an inverse relationship between levels of anti-tissue transglutaminase IgA (TTG) antibodies and fetal growth (Gastroenterol 2013; 144: 726-35).

Results:

  • Newborns of positive TTG (>6 U/mL) weighed 159 g less at birth than newborns of mothers who tested negative for TTG.  In addition, newborns with mothers who had intermediate TTG levels ( 0.8 U/mL to 6 U/mL) had growth restriction of 53 g.
  • Among the intermediate TTG group, the results were more pronounced (2-fold greater) in those carrying the HLA risk molecules for celiac disease.
  • These birth weight changes were not associated with maternal nutritional status or deficiencies related to hemoglobin, iron, folate, or vitamin B12 deficiency.
  • Gestational age was not affected by TTG titers.

In the discussion, the authors note that other studies have shown that undiagnosed celiac disease increases the risk for intrauterine growth retardation; this risk can be eliminated by treating celiac disease.  The latter is a risk factor for lower neuropsychological performance.  This study was the first that took into effect the different TTG titers and correlated with additional nutritional parameters.

The authors speculate that celiac disease could have direct effects on the placenta.  In addition, other nutritional parameters could play a role such as vitamin D and calcium which were not included in this study.  Another important consideration is that celiac disease can result in increased miscarriages.  As a result, the “true” effect on newborn growth may be underestimated due to a “survivor bias.”

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Nuance in Celiac Serology Interpretation

A recent study adds additional nuance to the interpretation of celiac serology (Clin Gastroenterol Hepatol 2013; 11: 398-403).

In this study the authors analyzed anti-TTG IgA levels from 104 consecutive pediatric and adult patients who were not IgA deficient.  The study took place between 2000-2009.  In addition, samples from 537 consecutive controls were available for comparison.

The study determined the likelihood of having celiac disease based on antibody level from four different companies and pre-test clinical factors.  The general population pretest probability was 1%; the pretest probability for their population was 6% if their were gastrointestinal complaints, 14% if weight loss/small stature was present, 11% for patients with anemia/iron deficiency, and 9% for patients with malabsorption.

Key findings:

Even in those with high antibody titers (>10-fold normal), if they were asymptomatic, only 53%-75% had celiac disease (depending on the individual assay).  That is, >10-fold elevation with some commercial assays did not correspond to >10-fold elevation in all of the assays leading to variable probabilities.

In patients with low level elevations (1-3 fold times the cut-off level), the probability of having celiac disease in asymptomatic individuals varied from 1% to 7%.  Thus, mild elevations in TTG IgA are not highly predictive in this asymptomatic population.  However, in those with pretest probability of 14%, the frequency of celiac disease varied among the four assays from 14% to 56%.

Take home message:  Not all assays for celiac disease are comparable.  While very high serology levels (>10 fold) are associated with celiac disease, in asymptomatic patients as few as 53% may have celiac disease.

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Expert review: Celiac disease

A recent article gives a concise expert update on Celiac disease (NEJM 2012; 367: 2419-26).

As this is an area that has been covered several times by this blog and is familiar to most of the followers, I will comment on a few issues that were particularly interesting to me.  Though, the review is thorough and a helpful reference on most aspects of celiac disease..

What is the gluten threshold?  In patients with celiac disease, a minimal degree of gluten contamination is difficult to avoid.  “The lowest amount of daily gluten that causes damage to the celiac intestinal mucosa over (the gluten threshold) is 10 to 50 mg per day (a 25-g slice of bread contains approximately 1.6 g of gluten).”  New regulations propose that foods which are labeled as gluten free have less than 20 ppm of gluten contamination.

When are intraepithelial lymphocytes increased in the duodenum?  The abnormal threshold is considered >25 per 100 enterocytes.

What proportion of celiac disease patients have been diagnosed?  According to a recent European study, only a small proportion (21%) of celiac patients are clinically recognized.

Best screening test currently? Anti-tissue transglutaminase (TTG) IgA antibody –both sensitivity and specificity are >95%.  Consider TTG IgG in patients with IgA deficieny or possibly deamidated gliadin IgG.

Potential complications of untreated celiac disease? Osteoporosis, impaired splenic function, neurologic disorders, infertility or recurrent abortion, ulcerative jejunoileitis, and cancer.

Biopsy needed? Usually, “although recent guidelines suggest that biopsy may not be necessary in selected children with strong clinical and serologic evidence of celiac disease.”

Population-based screening or case-finding?  At this time, population-based screening is not recommended.  Case-finding based on symptoms and screening of at-risk groups is recommended though this is likely to miss >50% of cases.

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False-positive serology for Celiac disease

It is prudent to exercise caution in establishing a diagnosis of Celiac disease (CD) in young asymptomatic children who are identified with screening serology (J Pediatr 2012; 161: 980-14).

In this Italian study, a nationwide, multicenter, prospective intervention trial was established to assess the role of age at gluten introduction on development of CD.  Subjects were recruited at birth who were at increased risk for CD; they had at least one first-degree relative with CD.

In their cohort, 96 children were identified.  In addition to having an affected first-degree relative, all children had positive serology (21 with positive tissue transglutaminase IgA antibody [tTG] and 1 with IgA deficiency/positive gliadin IgG antibody) and results of a small intestinal antibody.

While 72 had definitive CD, 24 were considered potential CD (serology positive/Marsh 0-1 histology) and asymptomatic.  The fascinating part of this study was the followup of the potential CD cases –21/24 continued on a regular diet.  Only 1 developed overt CD. 18 (86%) developed normal serology and 2/21 had fluctuating antibody levels after two years.

Based on their findings as well as consensus guidelines, the authors propose that asymptomatic young patients with abnormal serology should be followed for at least 3-6 months as long as tTG < 11 times ULN.

Other findings:

  1. Breastfeeding may have a protective role; individuals with overt CD had a shorter mean duration of breastfeeding than the potential CD group (4.2 months compared with 5.1 months).
  2. Gluten introduction at age 6 months did not increase risk of overt CD (compared to potential CD) relative to introduction at 12 months.

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