X CHROMOSOME - SCI &
TECH
News: X chromosome revival in older
women increases autoimmune disease risk
What's in the news?
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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.
X Chromosome:
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It is one of the two sex chromosomes in humans, the other being the Y chromosome.
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Females have two X chromosomes (XX), while males have one X and one Y chromosome
(XY).
Genetic Landscape of the
X Chromosome:
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The human X chromosome encodes around 800 genes, producing proteins.
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Loss of function in these genes can lead to various
genetic diseases.
Diseases:
Diseases influenced by the X chromosome fall into three categories such as
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X-linked genetic diseases.
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Diseases influenced by XCI (X chromosome
inactivation) escape.
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Diseases linked to X-chromosome aneuploidy.
Significance:
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Encodes around 800 genes that are crucial for
various biological processes.
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Plays a significant role in determining sex and
influencing many physiological functions.
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Loss of function or mutations in X chromosome genes can lead to several
genetic disorders.
Autoimmune Diseases:
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Diseases where the immune system mistakenly attacks the body’s own cells and tissues.
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Normally, the immune system defends against
infections by targeting harmful pathogens.
Common Autoimmune
Diseases:
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Systemic Lupus Erythematosus (SLE) - Chronic inflammation
affecting various body parts.
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Rheumatoid Arthritis (RA) - Inflammation of
joints and surrounding tissues.
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Sjogren’s Syndrome - Affects glands that produce
moisture, leading to dry mouth and eyes.
How does the X
chromosome cause Autoimmune Diseases?
1. X Chromosome
Inactivation (XCI):
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In females, one of the two X chromosomes is
randomly inactivated during early
embryonic development to balance gene expression between males and females.
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This process is crucial to prevent overexpression
of X-linked genes.
2. XCI Escape:
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Not all genes on the inactive X chromosome are
completely silenced.
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Up to a fourth of these genes may escape
inactivation and continue to be expressed.
Link to Autoimmune
Diseases:
1. Skewed XCI:
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Uneven inactivation of X chromosomes may lead to an
imbalance in gene expression, contributing to autoimmune disorders.
2. Incomplete XCI:
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Reactivation of genes that should be silenced can
result in abnormal immune responses.
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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:
1. Sex Bias in Alzheimer’s:
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Women are almost twice as likely as men to develop
Alzheimer’s disease.
2. Role of X-Linked
Genes:
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Researchers have identified a gene called ubiquitin-specific peptidase 11 (USP11)
on the X chromosome.
3. USP11 Gene:
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Involved in protein
modification processes and thought to influence the accumulation of tau
proteins in the brain.
4. XCI Escape:
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USP11 may escape XCI in females, leading to higher expression levels and contributing
to Alzheimer’s pathology.
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A study from Case Western Reserve University (Cell,
October 2022) highlighted this mechanism, suggesting it as a target for new
treatments.
Go back to basics:
Chromosomes:
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Chromosomes are fundamental components of cells
that play a vital role in storing and
transmitting genetic information.
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These structures contain genes, which carry
instructions for the development, functioning, and inheritance of traits.
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Chromosomes consist of tightly coiled DNA molecules wrapped around proteins called
histones, forming chromatin.
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Before cell division, chromosomes replicate into
identical sister chromatids held together at the centromere.
Types of Chromosomes:
1. Autosomes:
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Non-sex chromosomes (22 pairs in humans) determine
most traits.
2. Sex Chromosomes:
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Determine biological sex (XX for females, XY for
males).
Functions of
Chromosomes:
1. Genetic Information
Storage:
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Genes on chromosomes encode instructions for
protein production and cellular processes.
2. Inheritance:
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Chromosomes transmit genetic information during
sexual reproduction through meiosis, ensuring genetic diversity in offspring.
3. Gene Expression
Regulation:
● Chromosomes control gene activation or silencing, crucial for development and cell functioning.