Chronic hepatitis B infection and autoimmune thyroiditis in Down syndrome

Although it is well known that viral hepatitis can be complicated by autoimmune phenomena, the evidence for a pathogenetic role of viral hepatitis in the etiology of autoimmune thyroiditis is unclear. Because both hepatitis B and autoimmune thyroiditis occur frequently in Down syndrome, we decided to determine whether a cause-and-effect relationship might exist. Such a relationship might provide insight into basic mechanisms that could generalize to other populations. Accordingly, the frequency of hepatitis B surface antigen (HBsAg) positivity and thyroiditis was determined in 57 adults with Down syndrome and compared with frequencies in 450 age-, sex-, and environmentally matched mentally retarded patients without Down syndrome. We found no relationship of HBsAg positivity and thyroiditis in those mentally retarded patients without Down syndrome. On the other hand, the frequency of thyroiditis in those Down syndrome patients who were also carriers of HBsAg was threefold higher than the frequency of thyroid disease in those patients with Down syndrome who were not carriers of HBsAg (65% vs. 23%, p < 0.01). This relationship of hepatitis B and thyroid disease in Down syndrome might be explained by cytokine and/or cellular immune abnormalities linked to extra genetic material in trisomy 21. Clinically, patients with Down syndrome who are also hepatitis B carriers should be closely monitored for development of thyroid disease.