Gliadin antibody (GA) tests used in screening for coeliac disease (CD) frequently yield positive GA results without accompanying CD in cases of
diabetes mellitus type 1 (DM-1). To enlighten this phenomenon we screened 848 DM-1 patients for
IgA- and
IgG-GA. Subsequently, 16 out of 19 high titre GA patients (6 with CD) were compared with 37 low titre DM-1 patients matched for sex, age and disease duration, for autoimmune and immunogenetic markers.
Chronic thyroiditis and
thyroid peroxidase (TPO) antibody positivity were more frequent in the GA-positive than in the GA-negative sub-group (38 vs. 2.7%, p = 0.003, and 69 vs. 27%, p < 0.00, respectively). The
tissue transglutaminase (tTg)
IgA titres correlated with CD but not with GA. tTg
IgG titres were lower in GA-positive individuals (p = 0.0012). GA-positivity correlated with a higher titre of
factor XIII IgA antibodies (p < 0.001). GA-positive DM-I patients were characterised by a distinct immunogenetic profile; the risk of
HLA DQB1*02 was lower among GA-positive patients than among GA-negatives (OR 0.4, preventive fraction 0.43). All CD patients were
HLA DRB1*03-DQB1* 02-positive, but none of the five patients with normal biopsies. GA-positive patients instead had
HLA DRB1*13 in 37.5% as compared to 8.6% in GA-negative (OR 6.4, etiologic fraction 0.32). Thus, the occurrence of positive GA in DM-1 is correlated to TPO antibody positivity,
thyroiditis and
factor XIII IgA antibodies, but inversely correlated to tTg
IgG, and seems to be associated with another HLA haplotype than that previously found to be associated with CD.