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Related Concept Videos

Pedigree Analysis

Pedigree Analysis

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”.

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 and Y Chromosomes

X and Y Chromosomes

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.
The germline cells such as egg and sperm cells carry only half the number of chromosomes, i.e., 22 autosomes and one sex chromosome. All eggs have an X chromosome, while sperm cells can carry an X or...

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”.

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.

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A Non-random Mouse Model for Pharmacological Reactivation of Mecp2 on the Inactive X Chromosome

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X-linked mental retardation syndrome with characteristic "coarse" facial appearance, brachydactyly, and short stature

N J Carpenter¹, Y Qu, M Curtis

¹H.A. Chapman Institute of Medical Genetics, Tulsa, Oklahoma 74135, USA.

American Journal of Medical Genetics

|July 9, 1999

Summary

This study identifies a novel X-linked mental retardation (XLMR) syndrome linked to the XNP gene, characterized by distinct facial anomalies and brachydactyly in affected males. Carrier females show skewed X-inactivation patterns.

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Published on: September 16, 2019

Area of Science:

Human Genetics
Medical Genetics
Molecular Biology

Background:

X-linked mental retardation (XLMR) encompasses a heterogeneous group of genetic disorders.
A three-generation family presented with XLMR, minor facial anomalies, and brachydactyly.

Purpose of the Study:

To identify the genetic locus and candidate gene responsible for XLMR in the described family.
To investigate the inheritance pattern and phenotypic characteristics of the syndrome.

Main Methods:

Microsatellite linkage analysis was performed using 16 loci across the X chromosome.
Recombination events were used to narrow down the disease locus.
X-inactivation studies were conducted on carrier females.
Phenotypic analysis of affected males and carrier females was performed.

Main Results:

Significant linkage was established to markers in the Xp11.3-Xq23 region.
The disease locus was localized between Xp11.3 and Xq23.
The XNP gene, associated with alpha-thalassemia/mental retardation syndrome (ATR-X), was identified as a strong candidate gene.
Carrier females exhibited completely skewed X-inactivation patterns.

Conclusions:

The findings suggest that mutations in the XNP gene are responsible for the XLMR syndrome in this family.
The syndrome presents with a distinct phenotype including coarse facial features, brachydactyly, short stature, and moderate mental retardation.
Skewed X-inactivation in carriers is a key indicator for XNP gene involvement.