Note4Students
From UPSC perspective, the following things are important :
Prelims level: Autoimmune Diseases, X Chromosome
Mains level: NA
Why in the News?
The X chromosome influences biological functions and disease susceptibilities, affecting genetic disorders, autoimmune diseases, and Alzheimer’s, with research offering potential new treatments and therapies.
Back2Basics: Chromosomes
Types of Chromosomes:
Functions of Chromosomes
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Genetic Landscape of the X chromosome:
- The human X chromosome encodes around 800 genes, producing proteins.
- Loss of function in these genes can lead to various genetic diseases.
- Diseases influenced by the X chromosome fall into three categories:
- X-linked genetic diseases
- Diseases influenced by XCI (X chromosome inactivation) escape
- Diseases linked to X-chromosome aneuploidy
What is the X chromosome?
- It is one of the two sex chromosomes in humans, the other being the Y chromosome.
- Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
- Significance:
- Encodes around 800 genes that are crucial for various biological processes.
- Plays a significant role in determining sex and influencing many physiological functions.
- Loss of function or mutations in X chromosome genes can lead to several genetic disorders.
What are Autoimmune Diseases?
- Diseases where the immune system mistakenly attacks the body’s own cells and tissues.
- Normally, the immune system defends against infections by targeting harmful pathogens.
- Common Autoimmune Diseases:
- Systemic Lupus Erythematosus (SLE): Chronic inflammation affecting various body parts.
- Rheumatoid Arthritis (RA): Inflammation of joints and surrounding tissues.
- Sjogren’s Syndrome: Affects glands that produce moisture, leading to dry mouth and eyes.
How does the X chromosome cause Autoimmune Diseases?
- X Chromosome Inactivation (XCI):
- In females, one of the two X chromosomes is randomly inactivated during early embryonic development to balance gene expression between males and females.
- This process is crucial to prevent overexpression of X-linked genes.
- XCI Escape:
- Not all genes on the inactive X chromosome are completely silenced.
- Up to a fourth of these genes may escape inactivation and continue to be expressed.
- Link to Autoimmune Diseases:
- Skewed XCI: Uneven inactivation of X chromosomes may lead to an imbalance in gene expression, contributing to autoimmune disorders.
- Incomplete XCI: Reactivation of genes that should be silenced can result in abnormal immune responses.
Studies, such as one published in Science Advances (May 3, 2023), have shown that reactivation of X-linked genes in immune cells can lead to lupus-like symptoms in mice.
Linkage between X chromosome and Alzheimer’s disease
- Sex Bias in Alzheimer’s:
- Women are almost twice as likely as men to develop Alzheimer’s disease.
- Role of X-Linked Genes:
- Researchers have identified a gene called ubiquitin-specific peptidase 11 (USP11) on the X chromosome.
- USP11 Gene: Involved in protein modification processes and thought to influence the accumulation of tau proteins in the brain.
- XCI Escape: USP11 may escape XCI in females, leading to higher expression levels and contributing to Alzheimer’s pathology.
- A study from Case Western Reserve University (Cell, October 2022) highlighted this mechanism, suggesting it as a target for new treatments.
PYQ:[2011] At present, scientists can determine the arrangement or relative positions of genes or DNA sequences on a chromosome. How does this knowledge benefit us?
Which of the statements given above is/are correct? (a) 1 and 2 only (b) 2 only (c) 1 and 3 only (d) 1, 2 and 3 |
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