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X chromosome & Autoimmune Disease Risk
Context
In mammals, including humans, the X chromosome plays a crucial role beyond determining sex. However, recent genomic studies have shown that the X chromosome influences various biological processes and affects susceptibility to certain diseases.
Genes and Diseases
- The human X chromosome encodes around 800 genes, which produce proteins essential for various bodily functions. When these genes malfunction, they can cause numerous genetic diseases.
- Diseases influenced by the X chromosome can be grouped into three types:
- X-linked Genetic Diseases There are over 500 known X-linked genetic diseases, predominantly affecting males. Common examples include: Red-green colour blindness, Duchenne muscular dystrophy, Agammaglobulinemia (immunodeficiency disorder)
- Diseases linked to X-chromosome aneuploidy: Aneuploidies are numerical abnormalities of the X chromosome, such as:
- Klinefelter syndrome: Characterized by an extra X chromosome (XXY).
- Turner’s syndrome: Characterized by the loss of one X chromosome in females (X instead of XX).
- Diseases influenced by X chromosome inactivation (XCI) escape: In 1961, geneticist Mary Frances Lyon discovered that one of the X chromosomes in females is randomly inactivated during early embryonic development to prevent overexpression of X-linked genes. This process, called X chromosome inactivation (XCI), involves epigenetic changes that silence most genes on one X chromosome.
- Autoimmune Diseases: Autoimmune diseases, where the body's immune system attacks its own tissues, are more common in females. Examples include systemic lupus erythematosus, rheumatoid arthritis, and Sjögren’s syndrome. Altering XCI can lead to the reactivation of previously inactive genes, contributing to these diseases.
- Alzheimer’s Disease: Alzheimer’s disease, which affects more women than men, is also linked to the X chromosome.
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