Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 21, one copy inherited from each parent, form one of the pairs. Chromosome 21 is the smallest human chromosome, spanning about 47 million base pairs (the building blocks of DNA) and representing approximately 1.5 percent of the total DNA in cells.
In 2000, researchers working on the Human Genome Project announced that they had determined the sequence of base pairs that make up this chromosome. Chromosome 21 was the second human chromosome to be fully sequenced.
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. Chromosome 21 likely contains between 300 and 400 genes.
Genes on chromosome 21 are among the estimated 20,000 to 25,000 total genes in the human genome.
At first glance, Down syndrome and Alzheimer's disease, two severe brain abnormalities, may seem to have little in common. Down syndrome is a hereditary disease, the source of which has long been recognized--a triplication of chromosome 21.
Down's syndrome - also known as trisomy 21 - is a genetic disorder caused by an additional third chromosome 21. Although this genetic abnormality is found in one out of 700 births, only 20% of foetuses with trisomy 21 reach full term.
Some scientists call it the "final frontier" of our DNA -- even though it lies at the center of every X-shaped chromosome in nearly every one of our cells.
Research by Jue Wang, MD, at the University of Arizona Cancer Center at Dignity Health St. Joseph's Hospital and Medical Center on "Delay in Diagnosis of Testicular Cancer in a Patient with Down Syndrome" was published in the October issue of Journal of Cancer and Therapeutic Science.
Most living cells have a defined number of chromosomes: Human cells, for example, have 23 pairs. As cells divide, they can make errors that lead to a gain or loss of chromosomes, which is usually very harmful.
A phase 2 clinical trial in young adults with Down syndrome of a drug being investigated for the treatment of Alzheimer's disease supports further investigation of its potential.
Findings from new research led by the Monash Biomedicine Discovery Institute and University College London may finally resolve, and potentially provide answers, as to why older women have higher incidences of miscarriage and have babies with chromosomal abnormalities.
Ayahuasca is a beverage that has been used for centuries by Native South-Americans. Studies suggest that it exhibits anxiolytic and antidepressant effects in humans.
For women in their 30s and beyond, the probability of a pregnancy that results in a miscarriage or a Down syndrome pregnancy is staggering with the risk increasing to 1 in 3 by the time a woman reaches her early 40s due to the "maternal age effect," the high incidence of mistakes in chromosome segregation that occur during the cell division process of meiosis, which gives rise to the egg.
GENETICISTS have identified an enzyme which regulates the production of sperm and egg cells in human reproduction.
Biomarkers play an important role in modern cancer medicine. They are used as tools to diagnose cancers more precisely and to better predict the course of the disease.
RESEARCHERS have identified the gene they believe is responsible for the onset of type 2 diabetes, sparking hope for treatments to prevent and possibly reverse the progressive condition.
Abnormal cells in the early embryo are not necessarily a sign that a baby will be born with a birth defect such as Down's syndrome, suggests new research carried out in mice at the University of Cambridge. In a study published today in the journal Nature Communications, scientists show that abnormal cells are eliminated and replaced by healthy cells, repairing - and in many cases completely fixing - the embryo.
Scientists at the University of Cambridge have for the first time shown that it is possible to derive from a human embryo so-called 'naïve' pluripotent stem cells - one of the most flexible types of stem cell, which can develop into all human tissue other than the placenta.
While most Down syndrome research has focused on the brain, a new report by Johns Hopkins University biologists uncovers how the disorder hampers a separate part of the nervous system that plays a key role in health and longevity.
There is increasing evidence that the brain changes of Alzheimer's disease begin decades before memory and thinking problems occur, prompting the need for better methods of early detection for this progressive, fatal brain disease. Consequently, there is a growing school of thought that the most effective future Alzheimer's drug therapies will be administered to those who are at high risk of the disease before cognitive symptoms appear.
Pediatric researchers have developed the first set of growth charts for U.S. children with Down syndrome since 1988. These new charts provide an important tool for pediatricians to evaluate growth milestones for children and adolescents with this condition. With these new charts, pediatricians will be able to compare each patient's growth patterns with peers of the same age and sex who have Down syndrome.
For people with Down syndrome, news from Elixirgen, LLC may brighten their day. The biotechnology company, located in the Science + Technology Park at Johns Hopkins, has outlined one of the best potential therapies yet for people with Down syndrome and other chromosome disorders in a paper entitled, "Correction of Down syndrome and Edwards syndrome aneuploidies in human cell cultures," published in the journal DNA Research.
The term intellectual disability covers a large number of clinical entities, some with known cause and others of uncertain origin. For example Down syndrome is due to an extra copy of chromosome 21 and Rett syndrome is in part caused by a mutation in the control switch gene called MeCP2.
Researchers at the University of Kentucky's Sanders-Brown Center on Aging have completed a study that revealed differences in the way brain inflammation -- considered a key component of AD-- is expressed in different subsets of patients, in particular people with Down syndrome (DS) and AD.