Objectives Associations between autoimmune thyroid disease and antigens of
the major histocompatibility complex (MHC) have long been recognized. Grave
s' disease (GD) is associated with the histocompatibility leucocyte antigen
(HLA) haplotype A*01-B*0801-DRB1*0301-DQA1*0501-DQB1*0201 (or B8/DR3) wher
eas autoimmune hypothyroidism (AIH) has been weakly associated with HLA DRB
1*03, *04 and *11/*12 alleles (or DR3, DR4 and DR5). However, the presence
of important immunoregulatory genes within the HLA Class II and III regions
raises the possibility that these genes harbour the primary susceptibility
locus. This study examines genetic variation across the MHC in UK Caucasoi
d subjects with autoimmune thyroid disease.
Patients and Methods DNA extracted from venous blood samples from 215 patie
nts with autoimmune thyroid disease (GD 135, AIH 77) and 267 control subjec
ts was analysed. Genotyping was performed using polymerase chain reaction a
nd sequence specific primers for HLA Class I and II alleles and polymorphis
ms within the TAP1, TAP2, tumour necrosis factor (TNF), lymphotoxin alpha (
LT alpha), heat shock protein (HSP)70-1, HSP70-2 and HSP70-Hom genes.
Results For GD, the strongest association was with DRB1*03 [56% patients po
sitive vs. 24% controls, P = 2 x 10(-10), odds ratio (OR) 4.0]. Positive as
sociations were also seen for DRB1*03 linked alleles, B*0801, DRB3*01/02, D
QA1*05, DQB1*02 and DPB1*0101 (OR 2.3-3.4). Specific TNF and LT alpha allel
es were strongly associated with GD (P-c = 3 x 10(-5) and 0.001) and weak a
ssociations were seen for HSP70-1 + 190C and HSP70-2 + 1267G polymorphisms
(P-c = 0.05 and 0.01). These associations were not significant when DRB1*03
status was considered. Patients with AIH showed only a weak association wi
th DQB1*03 (P = 0.02).
Conclusions These results show that, of the polymorphisms tested within the
MHC, GD is most strongly associated with DRB1*03, and associations with ot
her immunoregulatory genes previously described in Caucasian subjects most
likely reflect linkage disequilibrium. AIH differs from GD, being less infl
uenced by the MHC region.