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Sex-linked Disorders

Sex-linked Disorders

Like autosomes, sex chromosomes contain a variety of genes necessary for normal body function. When a mutation in one of these genes results in biological deficits, the disorder is considered sex-linked.

X-linked Traits

X-linked Traits

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”.

X-linked Traits

X-linked Traits

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”.

Pedigree Analysis

Pedigree Analysis

X-Inactivation

X-Inactivation

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.

X-inactivation

X-inactivation

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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Related Experiment Video

Updated: Jul 6, 2026

A Robust Polymerase Chain Reaction-based Assay for Quantifying Cytosine-guanine-guanine Trinucleotide Repeats in Fragile X Mental Retardation-1 Gene

A Robust Polymerase Chain Reaction-based Assay for Quantifying Cytosine-guanine-guanine Trinucleotide Repeats in Fragile X Mental Retardation-1 Gene

Published on: September 16, 2019

Fragile X syndrome.

Kathryn B Garber¹, Jeannie Visootsak, Stephen T Warren

¹Department of Human Genetics, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322, USA.

European Journal of Human Genetics : EJHG

|April 10, 2008

Summary

This summary is machine-generated.

Fragile X syndrome stems from the FMR1 gene's silencing, leading to abnormal protein synthesis and synaptic dysfunction. This results in intellectual and emotional disabilities, including autism.

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Generation and Characterization of Human Induced Pluripotent Stem Cell-derived Astrocytes Lacking Fragile X Messenger Ribonucleoprotein

Generation and Characterization of Human Induced Pluripotent Stem Cell-derived Astrocytes Lacking Fragile X Messenger Ribonucleoprotein

Published on: June 6, 2025

Area of Science:

Neurogenetics
Molecular Biology
Developmental Disorders

Background:

Fragile X syndrome is an X-linked dominant disorder causing intellectual and emotional disabilities.
It results from the silencing of the FMR1 gene, often due to expanded CGG repeats.
The FMR1 gene product, FMRP, regulates protein synthesis in neuronal dendrites.

Purpose of the Study:

To elucidate the molecular mechanisms underlying Fragile X syndrome.
To understand the role of FMRP in neuronal development and function.

Main Methods:

Analysis of FMR1 gene expression and CGG repeat expansion.
Investigation of FMRP's RNA-binding properties.
Study of protein synthesis regulation in neuronal dendrites.
Examination of AMPA receptor trafficking and synaptic strength.

Main Results:

Transcriptional silencing of FMR1 due to CGG repeat expansion.
Absence of FMRP leads to dysregulated protein synthesis.
Over-translation of specific transcripts in FMRP-deficient neurons.
Abnormal AMPA receptor trafficking and reduced synaptic strength.

Conclusions:

FMR1 gene silencing and FMRP deficiency are central to Fragile X syndrome pathogenesis.
Dysregulated protein synthesis and synaptic abnormalities contribute to the fragile X phenotype.
Targeting FMRP function or downstream pathways may offer therapeutic strategies.