Celiac disease (CD) is a gluten-dependent immune-mediated enteropathy characterized by a typical but not unique lesion of the small intestinal mucosa, permanent intolerance to gluten, and full recovery with a gluten-free diet (1,2). The prevalence of CD, based on screening populations with serological markers, ranges between 0.5% and 1.3% (3), and is significantly higher in the presence of several genetic conditions, such as Down syndrome (DS) (3).
Down syndrome, also known as trisomy 21, has been associated with several gastrointestinal disorders (eg, duodenal atresia, Hirschsprung disease) and immune disorders (eg, insulin-dependent diabetes mellitus, autoimmune thyroiditis, Sjogren syndrome). Since 1975, several studies have reported a significantly high prevalence of CD in patients with DS (4). Depending on the screening strategy, CD has been reported in 4% to 17% of children with DS (5–11).
CD is prevalent in Arab populations (12,13) and is underdiagnosed in high-risk groups (14). The prevalence of serological markers for CD in Arab children with DS was found to be higher than 10% in 1 study (15), but only 1 of the 27 patients described underwent intestinal biopsy. Our study aims were to examine the prevalence of CD in Arab children diagnosed with DS compared with healthy Arab control subjects and to evaluate the contribution of immunoglobulin (Ig) IgA and IgG anti-gliadin antibodies (AGA), IgA and IgG tissue transglutaminase (TTG) antibodies, and IgA anti-endomysial antibodies (EMA) to screening for CD in children with DS.
PATIENTS AND METHODS
The study population included 52 Arab children with DS and 52 healthy Arab children who were recruited as control subjects. The local ethics committee approved the study protocol, and informed consent from children's parents or legal guardians was obtained before they were included in the study. Demographic and clinical data collected from each child included age, weight, height, gastrointestinal symptoms, and the presence of anemia or endocrine disorders.
In addition, 5 mL of venous blood was drawn for further analyses. The samples were centrifuged and stored at −80°C until testing. All of the samples were tested for IgA and IgG AGA, IgA and IgG TTG, and IgA EMA as described previously (16).
Immunoglobulin A and IgG antibodies against TTG were measured using a commercial enzyme-linked immunosorbent assay (Orgentec Diagnostika, Mainz, Germany) based on recombinant human TTG as an antigen. Values >15 U/mL were considered positive as established by the manufacturer.
Parents of children with positive TTG (IgA or IgG) were informed of these results and were advised to have their child undergo upper endoscopy with multiple duodenal biopsies. At that time, 5 mL of blood was drawn for DQ2 and DQ8 human leukocyte antigen (HLA) testing. In short, DNA typing was done to identify HLA DQB1*02 or DQB1*0302. Every case that was negative for both of these alleles was tested for DQA1*05.
The diagnosis of CD was established according to the current criteria published by the European Society of Pediatric Gastroenterology, Hepatology and Nutrition (17).
Differences between groups were evaluated with a 2-tailed Student t test. For single parameters, the Fisher exact test was used. P ≤ 0.05 was considered statistically significant.
The demographic, anthropometric, and clinical data of the study participants are presented in Table 1. Overall, gastrointestinal symptoms were present in 8 children with DS and 2 healthy control subjects (P = 0.09, not significant). Anemia (P = 0.06, not significant) and thyroid disorders (P = 0.11, not significant) were present only in children with DS.
The prevalence of positive AGA (IgA or IgG) was significantly higher in patients with DS compared with healthy control subjects (Table 1). TTG antibodies (IgG or IgA) were detected only in patients with DS, whereas IgA EMA was negative in all of the children (Table 1).
Children with DS who had positive TTG serology findings (n = 6) were 11 ± 5.4 years of age and had normal nutritional status (body mass index, 19.3 ± 3). Two reported symptoms of abdominal pain, 1 had anemia, and 1 had hyperthyroidism. Their serological results, HLA status, and histological findings are presented in Table 2. Only 5 of the 6 patients with DS underwent endoscopy with duodenal biopsies and HLA testing. Two of the 5 patients tested had typical CD histology (3.8%), 1 was HLA DQ2–positive, and the other tested negative for DQ2 and DQ8.
This study investigated the value of different serological markers in the diagnosis of CD in children with DS. The main findings of this study are that IgA TTG is a useful marker when screening for CD in patients with DS. In addition, the prevalence of CD in Arab patients with DS (3.8%) was 3 to 4 times higher than the prevalence of CD among the general population, and was in the lower range of CD prevalence in patients with DS reported in the literature (5–11).
Various serological markers and strategies have been used to diagnose CD in patients with DS, including AGA, EMA, and TTG antibodies. Historically, AGAs were the first used for screening of CD, but these antibodies were found in a large percentage of patients with DS with normal mucosal histology (9,18,19). In our cohort 23% of patients with DS and 5% of control subjects were IgA AGA–positive, whereas 80% of patients with DS and 50% of control subjects were IgG AGA–positive. The existence of these antibodies in patients with DS with normal duodenal biopsy findings is probably the result of a general increase in immunoglobulin levels in these patients (20,21) related to an altered immune response or nonspecific mucosal anomalies resulting in gluten permeability (18,19). As a result of the high incidence of these antibodies in the general population and in patients with DS and because of the low specificity and sensitivity of these antibodies, intestinal biopsy based on screening with these antibodies is not recommended (19,22,23).
Tissue transglutaminase antibodies have been widely used in the last few years as a screening tool in the diagnosis of CD in the general population and in patients with DS because they are highly sensitive, inexpensive, and are easy to perform. In our study IgA TTG were positive in 9.6% of DS patients (5/52), whereas only 2 of these patients were diagnosed with CD (40%). Because the TTG-positive patients with normal histology were not available for follow-up, the true prevalence of CD in this cohort cannot be determined. Another obstacle to establishing the true prevalence of CD is that children with negative serological markers did not undergo biopsy. Because of this limitation, we could not calculate the sensitivity and specificity of the markers, but both had been reported to be high (24,25). Hansson et al had tested 52 DS patients and reported 98% sensitivity for IgA TTG, and similar results were found by Rumbo and colleagues (9,26). Recently, however, it was suggested that performance of TTG may be lower than previously reported and varies between laboratories (27). In that report sensitivity range was 40% to 86% and specificity was in the range of 42% to 100%. This may explain differences in the detection rate of patients with histological abnormalities between the various cohorts of DS patients.
Immunoglobulin G TTG was positive only in 1 patient with DS who had normal intestinal biopsy findings (but was HLA DQ2–positive), suggesting that IgG TTG is not useful in CD screening in patients with DS. These findings are in agreement with other investigators that showed these antibodies to be of low value in screening patients with DS as a result of low sensitivity and specificity (9,18,19). Rumbo et al found that 11 of 56 patients with DS were IgG TTG–positive but only 2 of 56 were IgA TTG–positive and were diagnosed with CD, indicating a high false-positive rate with these antibodies (9).
The prevalence of IgA deficiency among patients with CD is estimated to be 5% (2). Therefore, in our study design we elected to measure IgG AGA and IgG TTG rather than measure IgA levels as suggested by others (28,29). In addition, we performed these measurements (ie, total IgA) only in IgG AGA–positive or TTG-positive patients. The high prevalence of IgG AGA in both study groups and the low value of IgG TTG demonstrate such an algorithm to be impractical.
In this study IgA EMA was negative in patients with DS and control subjects. Thus, in our cohort, the use of EMA as the only screening marker would have missed the diagnosis of CD in the 2 patients who were IgA TTG–positive. EMAs are highly sensitive and specific serological markers for CD and have been used for screening in patients with DS and in the general population (5,19,23). However, several investigators have reported on patients diagnosed with CD with negative EMA, including a recent article that tested the prevalence of CD in Israel (16). We believe that the low sensitivity of EMA in our cohort is not a result of technical difficulties because in a cohort of infertile women treated by the same laboratory personnel and with the same equipment, EMA was more sensitive than TTG in the diagnosis of CD (14). Nevertheless, the possibility that the EMA-negative, IgA TTG–positive cases do not represent true CD cannot be ruled out.
More than 90% of patients with CD carry a variant of HLA-DQ2 and the rest carry HLA-DQ8. In patients who are positive for these HLA haplotypes, repeated serological marker testing is recommended (18,19,30–33), and it has been suggested that follow-up of patients with DS may be based on HLA testing (30). In our cohort 1 patient with DS diagnosed with CD did not have a classical HLA allotype, suggesting that such a strategy may miss patients with DS and CD. In agreement with our observation, it was recently reported that patients with DS may have typical histological findings without the typical HLA DQ allotype (34). However, in that study, only HLA-DQA1*0501 and DQB1*0201 were examined.
In summary, our study shows that IgA TTG is useful in diagnosing patients with CD and DS and that, similar to the findings of previous studies, there is a high prevalence of positive CD serology with compatible histology in these patients.
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