If a genetically identical twin develops rheumatoid arthritis, which mechanism dictates the likelihood that the other twin also develops the condition, despite identical genomes?

💡 Explanation

Rheumatoid arthritis concordance in identical twins is less than 50% because, although they share the same genome, epigenetic modifications (DNA methylation, histone modification) alter gene expression differently over time. Therefore, one twin can develop the disease while the other does not, rather than a guaranteed expression or solely based on genetic mutations.

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