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Related Concept Videos

Sex-linked Disorders01:43

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 Traits01:19

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 Traits01:19

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 Analysis01:35

Pedigree Analysis

Overview
Sex Linked Disorders01:43

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.
Lethal Alleles02:41

Lethal Alleles

Agouti: A Lethal Allele
Lucien Cuénot discovered lethal alleles in 1905 while studying the inheritance of coat color in mice. The agouti gene is responsible for the color of the coat in mice. This gene codes for an agouti-signaling protein, which is responsible for melanin distribution in mammals. The wild-type allele gives rise to gray-brown coat color in mice, while the mutant allele gives rise to yellow coat color. In addition to coat color, the agouti gene is associated with the yellow...

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Related Experiment Video

Updated: May 11, 2026

In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila
06:41

In Vivo Functional Study of Disease-associated Rare Human Variants Using Drosophila

Published on: August 20, 2019

X-linked mental deficiency.

Vincent des Portes1

  • 1Reference Center for Fragile X and other X-linked Intellectual Disabilities and Department of Pediatric Neurology, Hôpital Femme Mère Enfant, CHU de Lyon, Lyon, France.

Handbook of Clinical Neurology
|April 30, 2013
PubMed
Summary
This summary is machine-generated.

X-linked mental retardation (XLMR) accounts for 10% of male intellectual deficiency cases, with over 200 syndromes identified. Fragile X syndrome is the most common, characterized by specific genetic mutations and associated cognitive and language impairments.

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

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

Area of Science:

  • Genetics
  • Neurology
  • Developmental Biology

Background:

  • X-linked mental retardation (XLMR) represents a significant portion of intellectual deficiency cases in males, with over 200 identified syndromes.
  • Fragile X syndrome, the most prevalent XLMR, results from CGG triplet repeat amplification and is associated with cognitive and language deficits.

Purpose of the Study:

  • To review the genetic causes and clinical spectrum of X-linked mental retardation.
  • To highlight key XLMR syndromes and their associated genes.
  • To discuss the emerging diagnostic strategies for XLMR.

Main Methods:

  • Literature review of genetic and clinical data on X-linked mental retardation.
  • Analysis of identified XLMR genes and associated syndromes.
  • Synthesis of information on phenotypic variability and diagnostic approaches.

Main Results:

  • Over 80 genes are implicated in XLMR, contributing to diverse phenotypes.
  • Specific syndromes like Fragile X, Lowe, ATR-X, Allan-Herndon-Dudley, and those linked to ARX, MECP2, OPHN-1, and PQBP1 genes present with varied intellectual, neurological, and physical characteristics.
  • Clinical expression in females depends on X chromosome inactivation patterns.

Conclusions:

  • XLMR encompasses a wide range of genetic disorders with heterogeneous phenotypes.
  • Despite variability, a structured clinical diagnostic approach for XLMR is becoming increasingly feasible.
  • Understanding the genetic basis of XLMR is crucial for accurate diagnosis and potential therapeutic strategies.