| Brix and Hegedüs, Odense, Denmark, investigated the possible occurrence of genetic anticipation (i.e. a decrease in the age of onset as disease is passed through generations) in autoimmune thyroid disease (AITD). Seventy-four parent-child pairs with AITD from 57 multiple affected families were studied. Twenty-seven and 26 pairs were concordant for Graves' disease and Hashimoto's thyroiditis respectively. In the remaining 21 pairs, the clinical phenotype differed between parents and their offspring. Overall, mean age at diagnosis of AITD was 51.5 (range 16-78) years in the parents and 32.3 (range 16-60) years in the offspring (p < 0.001). Essentially similar results were obtained after subdividing the pairs into those concordant for Graves' disease and for Hashimoto's thyroiditis. Controlling for gender and smoking habits did not change the results. (Comment: Genetic anticipation has already been described for rheumatoid arthritis and chronic inflammatory bowel disease. This phenomenon has been linked to unstable expanded trinucleotide repeat sequences and the authors suggest to investigate this aspect as well in AITD.) Tait et al., Birmingham, UK, looked for coexistent AITD in the type I diabetes Warren Repository, being a DNA resource of 507 families for the identification of type 1 diabetes genetic determinants. In this repository they now looked for coexistent autoimmune disease and found this to be present in 72% of families. In 50% of these, the autoimmune disease was present in a first degree relative. The commonest coexisting disease was thyroid disease present in 34% of families. The distribution of type I diabetes over the gender of siblings was equal while autoimmune thyroid disease was 3 times more frequent in female siblings. Furthermore type I diabetes in a parent was 3 times more common in males but autoimmune thyroid disease about 2.5 times more frequent in mothers. The authors conclude that the high degree of clustering of different autoimmune diseases supports a common etiological mechanism. (Comment: The fact that distribution of type I diabetes is different over the sexes as compared to autoimmune thyroid disease suggests, apart from a common genetic susceptibility to autoimmune disease in general (see above), also the presence of different (other) etiological factors for both conditions.) |
