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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”.

Pleiotropy

Pleiotropy

Pleiotropy is the phenomenon in which a single gene impacts multiple, seemingly unrelated phenotypic traits. For example, defects in the SOX10 gene cause Waardenburg Syndrome Type 4, or WS4, which can cause defects in pigmentation, hearing impairments, and an absence of intestinal contractions necessary for elimination. This diversity of phenotypes results from the expression pattern of SOX10 in early embryonic and fetal development. SOX10 is found in neural crest cells that form melanocytes,...

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Related Experiment Video

Updated: May 25, 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

Capturing the fragile X premutation phenotypes: a collaborative effort across multiple cohorts.

Jessica Ezzell Hunter¹, Stephanie Sherman, Jim Grigsby

¹Department of Human Genetics, Emory University School of Medicine, Atlanta, GA, USA.

Neuropsychology

|January 19, 2012

Summary

Male carriers of the FMR1 premutation allele without FXTAS show no global executive function deficits. However, some carriers may have impaired inhibitory capacity, unrelated to age or repeat length.

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Area of Science:

Neurogenetics
Cognitive Neuroscience
Fragile X-associated Disorders

Background:

The FMR1 premutation allele (55-200 CGG repeats) is associated with various neurological conditions.
Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder affecting male carriers.
Neuropsychological profiles in male carriers without FXTAS are not fully understood.

Purpose of the Study:

To investigate the neuropsychological profile, specifically executive function, in male carriers of the FMR1 premutation allele who do not meet criteria for FXTAS.
To compare executive function performance between male carriers and non-carriers.

Main Methods:

A multicenter collaboration involving 3 independent cohorts.
100 male carriers of the FMR1 premutation allele and 216 non-carriers participated.
Standardized executive function tests were administered, including the Stroop Color-Word Test, Hayling Sentence Completion Test Part B, and Behavioral Dyscontrol Scale, with statistical models adjusting for cohort, age, and education.

Main Results:

Male carriers scored significantly lower than non-carriers on the Stroop Color-Word Test, Hayling Sentence Completion Test Part B, and Behavioral Dyscontrol Scale.
The Hayling test showed a significant age-related decline in carriers.
No specific age groups or repeat length ranges within the premutation were associated with increased risk for executive function deficits.

Conclusions:

Preliminary findings suggest no global executive function impairment in male FMR1 premutation carriers without FXTAS.
A subset of carriers may exhibit impaired inhibitory capacity.
Risk factors for this potential impairment do not appear to be linked to age or FMR1 repeat length.