AsianScientist (Dec. 26, 2017) – Scientists in Japan have demonstrated that autoimmune diseases affect identical twins differently due to epigenetics. They published their findings in Thyroid.
It does not matter if they are raised the same, fed the same, or dressed the same, identical twins have the same genes but they differ in the regulation and expression of those genes. This difference is caused by epigenetics—changes in gene function that are not encoded by the DNA sequence. Epigenetics also make twins different in their susceptibility to disease, including autoimmune diseases.
The thyroid is one of the critical centers for hormone production in the body. It has a fundamental role in the body’s metabolism and other functions, such as sleep and menstruation. Abnormalities in the thyroid are associated with autoimmune thyroid diseases, such as Grave’s disease and Hashimoto’s disease, wherein the body produces anti-thryoglobulin autoantibodies that cause the immune system to attack the patient.
In this study, a team of researchers led by Associate Professor Watanabe at the Center for Twin Research at Osaka University, Japan, has studied the epigenome of identical twins. They focused on gene polymorphisms, which are changes in the DNA bases, and the methylation of CpG sites, which is the chemical modification of DNA bases.
“We hypothesized that there are differences in the methylation of CpG sites. The methylation of CpG sites regulates gene expressions. Some diseases like type 1 diabetes show abnormal methylation patterns,” said Watanabe.
The researchers found that twin pairs with differing expression of anti-thryoglobulin autoantibodies (discordant pairs) bore 155 polymorphisms. Interestingly, none of these polymorphisms were located on chromosome 6, which contains human leukocyte antigen genes that are associated to autoimmunity.
For some of these polymorphisms, the researchers identified four CpG sites that were significantly different between discordant pairs. This suggests that autoimmune diseases in identical twin pairs are regulated by both genetic and epigenetic factors.
“Looking at only the genes is not enough. We need to study the genetics and epigenetics to determine the risk,” said Watanabe.
The article can be found at: Watanabe et al. (2017) Genotype-based Epigenetic Differences in Monozygotic Twins Discordant for Positive Anti-thyroglobulin Autoantibodies.
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Source: Osaka University; Photo: Pexels.
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