Sharing of susceptibility loci between autoimmune diseases: lack of association of the insulin gene region with Graves' disease

Genetic insights into disease mechanisms of autoimmunity

Educating the immune system to distinguish between self and non-self is critical to ensure that an immune response is mounted against foreign antigens and not against self. A breakdown in these mechanisms can lead to the onset of autoimmune disease. Clinical and molecular data suggest that shared immunogenetic mechanisms lead to the autoimmune process. The most studied genes and molecules are the human leukocyte antigen (HLA) region and the cytotoxic T-lymphocyte-associated 4 molecule (CTLA-4). Recently progress has been achieved in narrowing down the primary variants within both gene regions, but further work is needed to determine the function and extent of the aetiological variant(s) present. Recent exciting results also suggest a role for the newly discovered lymphoid-specific phosphatase (LYP) protein. As well as these general mechanisms, disease-specific mechanisms are beginning to be elucidated, for example the role of autoimmune regulatory element 1 (AIRE1) in autoimmune polyendocrinopathy-candidiasis ectodermal dystrophy (APECED). Taken together, these data suggest that both general and disease-specific mechanisms lead to the clinical outcome of autoimmune disease and that increased understanding of these mechanisms will improve our knowledge of how autoimmune disease occurs, eventually leading to the development of novel therapeutic agents.

Searching for the autoimmune thyroid disease susceptibility genes: from gene mapping to gene function

The autoimmune thyroid diseases (AITD) are complex diseases that are caused by an interaction between susceptibility genes and environmental triggers. Genetic susceptibility, in combination with external factors (e.g., dietary iodine), is believed to initiate the autoimmune response to thyroid antigens. Abundant epidemiological data, including family and twin studies, point to a strong genetic influence on the development of AITD. Various techniques have been used to identify the genes contributing to the etiology of AITD, including candidate gene analysis and whole genome screening. These studies have enabled the identification of several loci (genetic regions) that are linked with AITD, and in some of these loci putative AITD susceptibility genes have been identified. Some of these genes/loci are unique to Graves' disease (GD) and Hashimoto's thyroiditis (HT), and some are common to both diseases, indicating that there is a shared genetic susceptibility to GD and HT. The putative GD and HT susceptibility genes include both immune modifying genes (e.g., human leukocyte antigen, cytotoxic T lymphocyte antigen-4) and thyroid-specific genes (e.g., TSH receptor, thyroglobulin). Most likely these loci interact, and their interactions may influence disease phenotype and severity. It is hoped that in the near future additional AITD susceptibility genes will be identified and the mechanisms by which they induce AITD will be unraveled.

The genetics of autoimmune endocrine disease

The common autoimmune endocrinopathies result from an interaction between environmental factors and genetic predisposition. Several chromosomal gene regions have been shown to contribute to more than one disease, supporting the clinical observation that the autoimmune endocrine diseases cluster within individuals and families. Genetic studies have implicated the major histocompatability complex (MHC)-human leucocyte antigen (HLA) genes on chromosome 6p21, although this chromosomal region does not explain all of the genetic contribution to the various disorders. Non-MHC-HLA genes, including disease-specific loci, are beginning to be identified and the publication of the draft sequence of the human genome will undoubtedly expediate future discoveries. Combined with the establishment of large cohorts of subjects with disease and the development of technology capable of performing high-throughput genotyping, genetic studies are likely to impact on the future treatment and prevention of the common autoimmune endocrine diseases.

The genetics of Graves' disease

Graves' disease is a complex autoimmune disorder in which several genetic susceptibility loci and environmental factors are likely to contribute to the development of disease. HLA and the CTLA-4 gene region have been established as susceptibility loci, although the magnitude of their contributions seems to vary between data sets and geographic populations. Genome-wide searches are beginning to identify new loci, including GD-1, GD-2, and GD-3, although these loci have only been found in one data set. Additional loci are likely to be identified via a combination of genome-wide linkage analysis and allelic association analysis of candidate genes.