Objective: Abnormalities of immune function, including thyroid autoimmunity, are common features of Down's syndrome, and the genetic associations of autoimmune thyroiditis have been extensively studied in otherwise normal patients with thyroid disease. In this study we have examined the HLA associations of autoimmune thyroid diseases in a cohort of adult subjects with Down's syndrome, to see whether they differed from those found in other populations.
Design and measurements: Restriction fragment length polymorphism analysis was carried out in 41 subjects whose thyroid status was assessed by measuring thyroid function and autoantibody titres. The genotypes of subjects with and without hypothyroid autoimmune diseases were compared.
Subjects: Forty-one older subjects with Down's syndrome and an average age of 46.6 years under review by the Maudsley Hospital.
Results: Hypothyroid autoimmune disease in this study group was clearly associated with a 5.5-kb Taq1 DQA restriction fragment length polymorphism (Pc = 0.013) corresponding to the major histocompatibility (MHC) class II DQA 0301 allele.
Conclusions: In contrast to Hashimoto's thyroiditis and atrophic thyroiditis, there is a strong association between class II genotypes and hypothyroid autoimmune disease in Down's syndrome. This implies a role for a gene or genes on chromosome 21 in the development of autoimmune thyroid disease.