Chromosome X News and Research

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The X chromosome is one of the two sex chromosomes in humans (the other is the Y chromosome). The sex chromosomes form one of the 23 pairs of human chromosomes in each cell. The X chromosome spans about 155 million base pairs (the building blocks of DNA) and represents approximately 5 percent of the total DNA in cells.

Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes, while males have one X and one Y chromosome. Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in somatic cells (cells other than egg and sperm cells). This phenomenon is called X-inactivation or Lyonization. X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell. Because X-inactivation is random, in normal females the X chromosome inherited from the mother is active in some cells, and the X chromosome inherited from the father is active in other cells.

Some genes on the X chromosome escape X-inactivation. These genes are located at the tip of the short (p) arm of the X chromosome in an area known as the pseudoautosomal region. Although many genes are unique to the X or Y chromosome, genes in the pseudoautosomal region are present on both chromosomes. As a result, men and women each have two functional copies of these genes. Many genes in the pseudoautosomal region are essential for normal development.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. The X chromosome likely contains between 900 and 1,400 genes.

Genes on the X chromosome are among the estimated 20,000 to 25,000 total genes in the human genome.

Fragile X and Down syndrome appear to share common genetic cause

The two most prevalent forms of genetic mental retardation, Fragile X and Down syndromes, may share a common cause, according to researchers at Stanford University School of Medicine.

11 Apr 2007

Male births on the decline in the U.S. and Japan

A study published in this week's online edition of Environmental Health Perspectives reports that during the past thirty years, the number of male births has decreased each year in the U.S. and Japan.

10 Apr 2007

Lack of Olig1 protein in lung tumors may increase risk of death

A study of human lung tumors indicates that lung cancer patients who lack a particular protein may do more poorly than those with normal levels of that same protein.

2 Apr 2007

People who are pre-diabetic or who have Type 2 diabetes have much shorter telomeres

New genetic markers may be able to predict whether a person is likely to have coronary heart disease (CAD) in the future.

2 Apr 2007

Multiple genetic risk factors for prostate cancer found

A study led by researchers at the Keck School of Medicine of the University of Southern California (USC) and Harvard Medical School has identified seven genetic risk factors DNA sequences carried by some people but not others that predict risk for prostate cancer.

2 Apr 2007

Researchers identify gene for osteoporosis

Researchers report the identification of a gene that may play a role in susceptibility to osteoporosis, the crippling disease that leads to bone fractures, especially of the hip and spine.

31 Mar 2007

Genetic culprits of idiopathic pulmonary fibrosis

Scientists at Johns Hopkins have identified the genetic culprits that trigger a hereditary form of a fatal lung disease.

30 Mar 2007

Gene and a region of a chromosome identified that may lead to autism in children

Yale School of Medicine autism experts Fred Volkmar, M.D. and Ami Klin are part of a global research consortium from 19 countries to identify a gene and a region of a chromosome that may lead to autism in children.

13 Mar 2007

Old drug pentylenetetrazole may improve learning and memory in Down syndrome victims

Researchers in the United States have discovered that an old drug once used to study epilepsy substantially improved learning and memory in mice with Down syndrome symptoms.

26 Feb 2007

microRNA directly regulates a gene implicated in human cancers

MicroRNAs are tiny snippets of RNA that can repress activity of a gene by targeting the gene's messenger RNA (which copies DNA information and starts the process of protein production).

22 Feb 2007

Genetic tendency toward suicide linked to genome on chromosome 2

A Johns Hopkins-led study has found evidence that a genetic tendency toward suicide has been linked to a particular area of the genome on chromosome 2 that has been implicated in two additional recent studies of attempted suicide.

20 Feb 2007

Results of largest ever genome study of autism released

The genomes of the largest collection of families with multiple cases of autism ever assembled have been scanned and the preliminary results published in Nature Genetics. They provide new insights into the genetic basis of autism.

From The University of Manchester 19 Feb 2007

At last the culprit in Autism is revealed

An international team of scientists have discovered two new genetic links that may predispose children to develop autism.

19 Feb 2007

Largest collection of autism DNA

Preliminary findings from the largest genome scan ever completed in the history of autism research are being published in Nature Genetics. University of Pittsburgh researchers with a consortium of scientists from across the world contributed to this landmark research endeavor through the Autism Genome Project.

18 Feb 2007

Shortening chromosomes cause for earlier cancer onset in families with Li-Fraumeni syndrome

In families with a high incidence of Li-Fraumeni syndrome, the ends of individuals' chromosomes act somewhat like a lit fuse, according to researchers at The Hospital for Sick Children in Toronto. Their findings detail how telomeres, the ends of the chromosomes, shorten with every successive generation, leading to more severe cancers at an earlier age.

15 Feb 2007

Researchers discover master switch for a tumor suppressive network

A decades-old cancer mystery has been solved by researchers at Cold Spring Harbor Laboratory (CSHL). "We not only found a critical tumor suppressor gene, but have revealed a master switch for a tumor suppressive network that means more targeted and effective cancer therapy in the future," said CSHL Associate Professor Alea Mills, Ph.D.

11 Feb 2007

Horse genome sequence assembled

The first draft of the horse genome sequence has been deposited in public databases and is freely available for use by biomedical and veterinary researchers around the globe, leaders of the international Horse Genome Sequencing Project announced today.

7 Feb 2007

Scientists step closer to understanding the relationship between aging and cancer

Wielding a palette of chromosome paints, scientists at the Salk Institute for Biological Studies have taken a step closer to understanding the relationship between aging and cancer by visualizing chromosomes of cells from patients with a heritable premature aging disease known as Werner Syndrome.

6 Feb 2007

Gene found for Cornelia deLange syndrome

Studying mutations that give rise to a rare genetic disease, genetics researchers have identified a novel biological pathway that may have a broader role during human development, potentially in cases of mental retardation and autism.

5 Feb 2007

RNA used to turn on genes to alleviate disease

A new technique that employs RNA, a tiny chemical cousin of DNA, to turn on genes could lead to therapeutics for conditions in which nudging a gene awake would help alleviate disease, researchers at UT Southwestern Medical Center say.

28 Jan 2007