Reviewed February 2007
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 79 million base pairs (the building blocks of DNA) and represents between 2.5 percent 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 between 1,200 and 1,500 genes.
Genes on chromosome 17 are among the estimated 20,000 to 25,000 total genes in the human genome.
There are many genetic conditions related to genes on chromosome 17.
What chromosomal conditions are related to chromosome 17?
The following conditions are caused by changes in the structure or number of copies of chromosome 17.
Changes in chromosome 17 have been identified in several 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 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.
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 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.
A condition called Miller-Dieker syndrome results from a deletion of genetic material from a specific region of the short arm of chromosome 17 (written as 17p13.3) in each cell. Miller-Dieker syndrome is characterized by a problem with brain development in which the surface of the brain is abnormally smooth. This abnormality, called lissencephaly, leads to severe intellectual disability, significant developmental problems, and seizures. People with Miller-Dieker syndrome also have distinctive facial features, including a prominent forehead; a small, upturned nose; a long, thick upper lip; low-set and abnormally shaped ears; and widely spaced eyes. The loss of several genes on the short arm of chromosome 17, including the LIS1 gene, is likely responsible for the features of Miller-Dieker syndrome. Researchers are working to identify and characterize these genes.
A deletion of genetic material from the 17p13.3 region also has been found in some cases of isolated lissencephaly, which occurs without the other features of Miller-Dieker syndrome. Studies suggest that the deletion responsible for isolated lissencephaly tends to be smaller and include fewer genes than the deletion that causes Miller-Dieker syndrome. Both disorders involve a deletion of the LIS1 gene, however.
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.
Where can I find additional information about chromosome 17?
You may find the following resources about chromosome 17 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 17?
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
See How can I find a genetics professional in my area? in the Handbook.