What is chromosome 17?

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 17, one copy inherited from each parent, form one of the pairs. Chromosome 17 spans about 81 million DNA building blocks (base pairs) and represents between 2.5 and 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 17 likely contains 1,200 to 1,300 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.
Genes on chromosome 17 are among the estimated 20,000 to 25,000 total genes in the human genome.

How are changes in chromosome 17 related to health conditions?

Many genetic conditions are related to changes in particular genes on chromosome 17. This list of disorders associated with genes on chromosome 17 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 17.

acute promyelocytic leukemia

A type of blood cancer known as acute promyelocytic leukemia is caused by a rearrangement (translocation) of genetic material between chromosomes 15 and 17. This translocation, written as t(15;17), fuses part of the PML gene from chromosome 15 with part of the RARA gene from chromosome 17. This mutation is acquired during a person's lifetime and is present only in certain cells. This type of genetic change, called a somatic mutation, is not inherited. The t(15;17) translocation is called a balanced reciprocal translocation because the pieces of chromosome are exchanged with each other (reciprocal) and no genetic material is gained or lost (balanced). The protein produced from this fused gene is known as PML-RARα.
The PML-RARα protein functions differently than the protein products from the normal PML and RARA genes. The RARA gene on chromosome 17 provides instructions for making a transcription factor called the retinoic acid receptor alpha (RARα). A transcription factor is a protein that attaches (binds) to specific regions of DNA and helps control the activity (transcription) of particular genes. Normally, the RARα protein controls the activity of genes important for the maturation (differentiation) of immature white blood cells beyond a particular stage called the promyelocyte. The PML gene on chromosome 15 provides instructions for a protein that acts as a tumor suppressor, which means it prevents cells from growing and dividing too rapidly or in an uncontrolled way. The PML protein blocks cell growth and division (proliferation) and induces self-destruction (apoptosis) in combination with other proteins. The PML-RARα protein interferes with the normal function of both the PML and the RARα proteins. As a result, blood cells are stuck at the promyelocyte stage, and they proliferate abnormally. Excess promyelocytes accumulate in the bone marrow and normal white blood cells cannot form, leading to acute promyelocytic leukemia.

dermatofibrosarcoma protuberans

Translocation of genetic material between chromosomes 17 and 22, written as t(17;22), causes a rare type of skin cancer known as dermatofibrosarcoma protuberans. This translocation fuses part of the COL1A1 gene from chromosome 17 with part of the PDGFB gene from chromosome 22. The translocation is found on one or more extra chromosomes that can be either linear or circular. When circular, the extra chromosomes are known as supernumerary ring chromosomes. This mutation is acquired during a person's lifetime and is present only in certain cells. This type of genetic change, called a somatic mutation, is not inherited.
The fused COL1A1-PDGFB gene provides instructions for making a combined (fusion) protein that researchers believe ultimately functions like the active PDGFB protein. In the translocation, the PDGFB gene loses the part of its DNA that limits its activity, and production of the COL1A1-PDGFB fusion protein is controlled by COL1A1 gene sequences. As a result, the gene fusion leads to the production of a larger amount of active PDGFB protein than normal. Active PDGFB protein signals for cell growth and division (proliferation) and maturation (differentiation). Excess PDGFB protein abnormally stimulates cells to proliferate and differentiate, leading to the tumor formation seen in dermatofibrosarcoma protuberans.

Koolen-de Vries syndrome

Deletion of a small amount of genetic material (a microdeletion) on chromosome 17 can cause Koolen-de Vries syndrome. This disorder is characterized by developmental delay, intellectual disability, a cheerful and sociable disposition, and a variety of physical abnormalities.
Most people with Koolen-de Vries syndrome are missing a sequence of about 500,000 base pairs, also written as 500 kilobases (kb), at position q21.31 on chromosome 17. The exact size of the deletion varies among affected individuals, but it contains at least six genes including KANSL1. This deletion affects one of the two copies of chromosome 17 in each cell.
Because mutations in the KANSL1 gene cause the same signs and symptoms as the deletion, researchers have concluded that the loss of this gene accounts for the features of Koolen-de Vries syndrome. The protein produced from the KANSL1 gene is involved in controlling the activity of other genes and plays an important role in the development and function of many parts of the body. Although the loss of this gene impairs normal development and function, its relationship to the specific features of Koolen-de Vries syndrome is unclear.
While Koolen-de Vries syndrome is usually not inherited, most individuals with the condition caused by a deletion have had at least one parent with a common variant of the 17q21.31 region of chromosome 17 called the H2 lineage. This variant is found in 20 percent of people of European and Middle Eastern descent, although it is rare in other populations. In the H2 lineage, a 900 kb segment of DNA, which includes the region deleted in most cases of Koolen-de Vries syndrome, has undergone an inversion. An inversion involves two breaks in a chromosome; the resulting piece of DNA is reversed and reinserted into the chromosome.
People with the H2 lineage have no health problems related to the inversion. However, genetic material can be lost or duplicated when the inversion is passed to the next generation. Researchers believe that a parental inversion is probably necessary for a child to have the 17q21.31 microdeletion most often associated with Koolen-de Vries syndrome, but other, unknown factors are also thought to play a role. So while the inversion is very common, only an extremely small percentage of parents with the inversion have a child affected by Koolen-de Vries syndrome.

Miller-Dieker syndrome

Miller-Dieker syndrome is caused by a deletion of genetic material near the end of the short (p) arm of chromosome 17. The signs and symptoms of Miller-Dieker syndrome are related to the loss of multiple genes in this region. The size of the deletion varies among affected individuals. The loss of a particular gene on chromosome 17, called PAFAH1B1, is responsible for the syndrome's characteristic sign of lissencephaly, a problem with brain development in which the surface of the brain is abnormally smooth. The loss of another gene, called YWHAE, in the same region of chromosome 17 increases the severity of lissencephaly in people with Miller-Dieker syndrome. Additional genes in the deleted region contribute to the varied features of Miller-Dieker syndrome.

Smith-Magenis syndrome

Most people with Smith-Magenis syndrome have a deletion of genetic material from a specific part of chromosome 17 called the Smith-Magenis syndrome critical region. This region is located on the short (p) arm of chromosome 17 at position 11.2 (written as 17p11.2). Although this region contains multiple genes, researchers believe that the loss of one particular gene, RAI1, in each cell is responsible for most of the physical, mental, and behavioral features of Smith-Magenis syndrome. The loss of other genes in the deleted region may help explain why the signs and symptoms of this condition vary among affected individuals.

other cancers

Changes in chromosome 17 have been identified in several additional types of human cancer. These genetic changes are somatic, which means they are acquired during a person's lifetime and are present only in certain cells. A particular chromosomal abnormality called an isochromosome 17q occurs frequently in some cancers. This abnormal version of chromosome 17 has two long (q) arms instead of one long arm and one short (p) arm. As a result, the chromosome has an extra copy of some genes and is missing copies of other genes.
An isochromosome 17q is commonly found in a cancer of blood-forming tissue called chronic myeloid leukemia (CML). It also has been identified in certain solid tumors, including a type of brain tumor called a medulloblastoma and tumors of the brain and spinal cord known as primitive neuroectodermal tumors. Although an isochromosome 17q probably plays a role in both the development and progression of these cancers, the specific genetic changes related to cancer growth are unknown.

other chromosomal conditions

Other changes in the number or structure of chromosome 17 can have a variety of effects, including intellectual disability, delayed development, characteristic facial features, weak muscle tone (hypotonia), and short stature. These changes include an extra piece of chromosome 17 in each cell (partial trisomy 17), a missing segment of the chromosome in each cell (partial monosomy 17), and a circular structure called a ring chromosome 17. Ring chromosomes occur when a chromosome breaks in two places and the ends of the chromosome arms fuse together to form a circular structure.

Is there a standard way to diagram chromosome 17?

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.

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.

cancers

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.