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Related Concept Videos

X-Inactivation01:58

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The human X chromosome contains over ten times the number of genes as in the Y chromosome. Since males have only one X chromosome, and females have two, one might expect females to produce twice as many of the proteins, with undesirable results.
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Epigenetics is the study of inherited changes in a cell's phenotype without changing the DNA sequences. It provides a form of memory for the differential gene expression pattern to maintain cell lineage, position-effect variegation, dosage compensation, and maintenance of chromatin structures such as telomeres and centromeres. For example, the structure and location of the centromere on chromosomes are epigenetically inherited. Its functionality is not dictated or ensured by the underlying...
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In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.
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Dosage Compensation02:50

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In animals, gender is determined by the number and type of sex chromosome. For example, human females have two X chromosomes, and males have one X and one Y chromosome, whereas C.elegans with one X chromosome is a male, and the one with two X chromosomes is a hermaphrodite.
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In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.  
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Among mammals, the gender of an organism is determined by the sex chromosomes. Humans have two sex chromosomes, X and Y. Every human diploid cell has 22 pairs of autosomes and one pair of sex chromosomes. A human female has two X chromosomes, while a male has one X chromosome and one Y chromosome.
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Updated: Oct 17, 2025

A Non-random Mouse Model for Pharmacological Reactivation of Mecp2 on the Inactive X Chromosome
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Intelligence Quotient Variability in Klinefelter Syndrome Is Associated With GTPBP6 Expression Under Regulation of

Luciane Simonetti1, Lucas G A Ferreira1,2, Angela Cristina Vidi1,2

  • 1Department of Medicine, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil.

Frontiers in Genetics
|October 7, 2021
PubMed
Summary

Klinefelter syndrome (KS) patients with random X-chromosome inactivation (RXI) show higher GTPBP6 gene expression and lower IQ scores. Skewed XCI may protect against cognitive impairment in KS.

Keywords:
GTPBP6Klinefelter syndromeX-chromosome inactivationX-linked genesgene expressionintelligence quotient

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Area of Science:

  • Genetics
  • Neuroscience
  • Endocrinology

Background:

  • Klinefelter syndrome (KS) presents a wide range of clinical symptoms, including neurocognitive deficits.
  • The underlying mechanisms of neurocognitive dysfunction in KS are not fully understood.
  • X-chromosome gene expression imbalance is hypothesized to contribute to KS-related neurocognitive issues.

Purpose of the Study:

  • To investigate the relationship between X-chromosome inactivation (XCI) patterns, X-linked gene expression, and intelligence quotient (IQ) in individuals with KS.
  • To determine if XCI patterns influence neurocognitive performance in KS patients.
  • To identify specific X-linked genes associated with cognitive variability in KS.

Main Methods:

  • Evaluated 11 KS patients and 14 controls using IQ assessments.
  • Analyzed XCI patterns via HUMARA and ZDHHC15 gene assays.
  • Quantified expression of seven neurocognitive-related X-linked genes (GTPBP6, EIF2S3, ITM2A, HUWE1, KDM5C, GDI1, VAMP7) and XIST using blood RT-qPCR.

Main Results:

  • KS patients with random X-inactivation (RXI) exhibited lower average IQ scores compared to those with skewed X-inactivation (SXI).
  • Higher GTPBP6 gene expression was observed in KS patients with RXI compared to controls (p=0.0059).
  • GTPBP6 expression in KS patients with SXI did not differ from controls, suggesting a regulatory role of SXI.

Conclusions:

  • XCI patterns are associated with IQ variability in Klinefelter syndrome.
  • GTPBP6 gene expression is negatively correlated with full-scale IQ in KS, modulated by the XCI pattern.
  • Skewed X-inactivation may mitigate cognitive deficits in KS by regulating GTPBP6 expression, warranting further research.