sábado, 17 de agosto de 2013

Chromosome 16 - Genetics Home Reference

Chromosome 16 - Genetics Home Reference

Genetics Home Reference: your guide to understanding genetic conditions
Chromosome 16
Reviewed May 2010

What is chromosome 16?

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 16, one copy inherited from each parent, form one of the pairs. Chromosome 16 spans more than 90 million DNA building blocks (base pairs) and represents almost 3 percent of the total DNA in cells.
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 16 likely contains 800 to 900 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.
Genes on chromosome 16 are among the estimated 20,000 to 25,000 total genes in the human genome.

How are changes in chromosome 16 related to health conditions?

Many genetic conditions are related to changes in particular genes on chromosome 16. This list of disorders associated with genes on chromosome 16 provides links to additional information.
Changes in the structure or number of copies of a chromosome can also cause problems with health and development. The following chromosomal conditions are associated with such changes in chromosome 16.
alveolar capillary dysplasia with misalignment of pulmonary veins
Alveolar capillary dysplasia with misalignment of pulmonary veins (ACD/MPV) is a disorder that affects the development of blood vessels in the lungs. It can be caused by a deletion of genetic material on chromosome 16 in a region known as 16q24.1. This region includes several genes, including the FOXF1 gene. The protein produced from the FOXF1 gene is a transcription factor, which means that it attaches (binds) to specific regions of DNA and helps control the activity of many other genes. The FOXF1 protein helps regulate the development of the lungs and the gastrointestinal tract. Genetic changes that result in a nonfunctional FOX1 protein interfere with the development of pulmonary blood vessels and cause ACD/MPV. Affected infants may also have gastrointestinal abnormalities. Researchers suggest that deletions resulting in the loss of other genes in this region of chromosome 16 probably cause the additional abnormalities seen in some infants with this disorder. Like FOXF1, these genes also provide instructions for making transcription factors that regulate development of various body systems before birth.
Changes in the structure of chromosome 16 are associated with several types of cancer. These genetic changes are somatic, which means they are acquired during a person's lifetime and are present only in certain cells. In some cases, chromosomal rearrangements called translocations disrupt the region of chromosome 16 that contains the CREBBP gene. The protein produced from this gene normally plays a role in regulating cell growth and division, which helps prevent the development of cancers. Researchers have found a translocation between chromosome 8 and chromosome 16 that disrupts the CREBBP gene in some people with a cancer of blood-forming cells called acute myeloid leukemia (AML). Another translocation involving the CREBBP gene, which rearranges pieces of chromosomes 11 and 16, has been found in some people who have undergone cancer treatment. This chromosomal change is associated with the later development of AML and two other cancers of blood-forming tissues (chronic myelogenous leukemia and myelodysplastic syndrome). These are sometimes described as treatment-related cancers because the translocation between chromosomes 11 and 16 occurs following chemotherapy for other forms of cancer. A chromosomal rearrangement called an inversion has been identified in rare cases of AML. This inversion involves the breakage of chromosome 16 in two places; the resulting piece of DNA is reversed and re-inserted into the chromosome. This form of AML is characterized by a high rate of remission and a favorable outcome. Unlike the somatic changes described earlier, this chromosomal rearrangement may be inherited from a parent.
16p11.2 deletion syndrome
16p11.2 deletion syndrome is caused by a deletion of about 600,000 DNA building blocks (base pairs), also written as 600 kilobases (kb), at position 11.2 on the short (p) arm of chromosome 16. This deletion affects one of the two copies of chromosome 16 in each cell. The 600 kb region contains at least 25 genes, and in many cases little is known about their function. Researchers are working to determine the missing genes that contribute to the features of 16p11.2 deletion syndrome, which include delayed development, intellectual disability, and developmental disorders that affect communication and social interaction (autism spectrum disorders). Having a 16p11.2 deletion does not always lead to autism spectrum disorders or intellectual disability. Most people with the deletion have some of these symptoms, but others do not. Although some people have this deletion without serious consequences, they can still pass it to their children, who may be more severely affected.
Rubinstein-Taybi syndrome
Some cases of severe Rubinstein-Taybi syndrome (also known as chromosome 16p13.3 deletion syndrome) have resulted from a deletion of genetic material from the short (p) arm of chromosome 16. When this deletion is present in all of the body's cells, it can cause serious complications such as a failure to gain weight and grow at the expected rate (failure to thrive) and an increased risk of life-threatening infections. Affected individuals also have many of the typical features of Rubinstein-Taybi syndrome, including intellectual disability, distinctive facial features, and broad thumbs and first toes. Infants born with the severe form of this disorder usually survive only into early childhood. Several genes are missing as a result of the deletion in the short arm of chromosome 16. The deleted region includes the CREBBP gene, which is often mutated or missing in people with the typical features of Rubinstein-Taybi syndrome. Researchers believe that the loss of additional genes in this region probably accounts for the serious complications associated with severe Rubinstein-Taybi syndrome.
other chromosomal conditions
Trisomy 16 occurs when cells have three copies of chromosome 16 instead of the usual two copies. Full trisomy 16, which occurs when all of the body's cells contain an extra copy of chromosome 16, is not compatible with life. A similar but less severe condition called mosaic trisomy 16 occurs when only some of the body's cells have an extra copy of chromosome 16. The signs and symptoms of mosaic trisomy 16 vary widely and can include slow growth before birth (intrauterine growth retardation), delayed development, and heart defects. Duplication of the same 600 kb segment of chromosome 16 that is missing in 16p11.2 deletion syndrome may result in similar symptoms as the deletion in some individuals. People with this duplication may have developmental problems including autism spectrum disorder, language delay, and learning disability. The duplication appears to have a milder effect than the deletion, with a higher proportion of individuals with this chromosomal change showing no apparent disability. These individuals can still pass along the duplication to their children, who may have symptoms of this condition. Other changes in the number or structure of chromosome 16 can have a variety of effects. Intellectual disability, delayed growth and development, distinctive facial features, weak muscle tone (hypotonia), heart defects, and other medical problems are common. Frequent changes to chromosome 16 include an extra segment of the short (p) or long (q) arm of the chromosome in each cell (partial trisomy 16p or 16q) and a missing segment of the long arm of the chromosome in each cell (partial monosomy 16q).

Is there a standard way to diagram chromosome 16?

Geneticists use diagrams called ideograms as a standard representation for chromosomes. Ideograms show a chromosome's relative size and its banding pattern. A banding pattern is the characteristic pattern of dark and light bands that appears when a chromosome is stained with a chemical solution and then viewed under a microscope. These bands are used to describe the location of genes on each chromosome.

Where can I find additional information about chromosome 16?

You may find the following resources about chromosome 16 helpful. These materials are written for the general public.
You may also be interested in these resources, which are designed for genetics professionals and researchers.

Where can I find general information about chromosomes?

The Handbook provides basic information about genetics in clear language.
These links provide additional genetics resources that may be useful.

What glossary definitions help with understanding chromosome 16?

References (18 links)

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

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