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URL of this page: https://medlineplus.gov/genetics/chromosome/7/

Chromosome 7

Description

Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 7, one copy inherited from each parent, form one of the pairs. Chromosome 7 spans about 159 million DNA building blocks (base pairs) and represents more than 5 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 7 likely contains 900 to 1,000 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.

Health Conditions Related to Chromosomal Changes

The following chromosomal conditions are associated with changes in the structure or number of copies of chromosome 7.

7q11.23 duplication syndrome

7q11.23 duplication syndrome, a condition that can cause a variety of neurological and behavioral problems, is a result of an extra copy of a region on the long (q) arm of chromosome 7. This region is called the Williams-Beuren syndrome critical region (WBSCR) because its deletion causes a disorder called Williams syndrome (described below), also known as Williams-Beuren syndrome. The region, which is 1.5 to 1.8 million DNA base pairs (Mb) in length, includes 25 to 27 genes.

Extra copies of several genes in this region likely contribute to the characteristic features of 7q11.23 duplication syndrome.

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Greig cephalopolysyndactyly syndrome

Abnormalities of chromosome 7 are responsible for some cases of Greig cephalopolysyndactyly syndrome, a disorder that affects the development of the arms, legs, head, and face. These chromosomal changes involve a region of the short (p) arm of chromosome 7 that contains the GLI3 gene. This gene plays an important role in the development of many tissues and organs before birth.

In some cases, Greig cephalopolysyndactyly syndrome results from a rearrangement (translocation) of genetic material between chromosome 7 and another chromosome. Other cases are caused by the deletion of several genes, including GLI3, from the short arm of chromosome 7. The loss of multiple genes can cause a more severe form of this disorder called Greig cephalopolysyndactyly contiguous gene deletion syndrome. In addition to the characteristic features of the disorder, people with this form have seizures, developmental delays, and intellectual disabilities.

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Silver-Russell syndrome

Abnormalities of chromosome 7 can cause Silver-Russell syndrome, a rare condition that is characterized by slow growth before and after birth.

People normally receive one copy of chromosome 7 from each parent. For most genes on chromosome 7, both copies are expressed, or "turned on," in cells. For some genes on chromosome 7, however, only the gene derived from the sperm cell is expressed. For other genes, only the copy derived from the egg cell is expressed. These parent-specific differences in gene expression are known as genomic imprinting. 

In 7 percent to 10 percent of people with Silver-Russell syndrome, both copies of chromosome 7 come from the egg cell. This is known as uniparental disomy (UPD). UPD can cause people to have two active copies of some imprinted genes and no active copies of others. This imbalance in the activity of imprinted genes on chromosome 7 can cause the signs and symptoms of Silver-Russell syndrome.

Some people with Silver-Russell syndrome have a rearrangement, duplication, or deletion of genetic material on chromosome 7. These changes can also disrupt the normal activity of genes on chromosome 7, causing the signs and symptoms of Silver-Russell syndrome.

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Saethre-Chotzen syndrome

Abnormalities of chromosome 7 cause some cases of Saethre-Chotzen syndrome. This rare condition is characterized by the premature fusion of certain skull bones (craniosynostosis), which prevents the skull from growing normally and affects the shape of the head and face. The chromosomal changes involve a region of the short arm of chromosome 7 that contains the TWIST1 gene. This gene plays an important role in the early development of the head, face, arms, and legs.

The chromosome abnormalities responsible for Saethre-Chotzen syndrome include translocations of genetic material between chromosome 7 and another chromosome, a rearrangement of genetic material within chromosome 7 (an inversion), or the deletion of a segment of chromosome 7. Each of these chromosomal changes alters or deletes the TWIST1 gene and may also affect nearby genes.

When Saethre-Chotzen syndrome is caused by a chromosomal deletion instead of a variant within the TWIST1 gene, affected children are much more likely to have intellectual disabilities, developmental delays, and learning difficulties. These features are typically not seen when Saethre-Chotzen syndrome is caused by TWIST1 gene variants. Researchers believe that a loss of other genes on the short arm of chromosome 7 may be responsible for these additional features.

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Williams syndrome

The deletion of genetic material from the Williams-Beuren syndrome critical region at 7q11.23 causes Williams syndrome.  Features of this condition include mild to moderate intellectual disabilities or learning problems, unique personality characteristics, distinctive facial features, and heart and blood vessel (cardiovascular) problems. Researchers believe that the loss of several of the genes in this region cause the signs and symptoms of Williams syndrome.

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Other chromosomal conditions

Other changes in the structure or number of copies of chromosome 7 can cause delayed growth and development, intellectual disabilities, distinctive facial features, skeletal abnormalities, delayed speech, and other health problems. Changes in chromosome 7 include an extra copy of some genetic material from this chromosome in each cell (partial trisomy 7) or a missing segment of the chromosome in each cell (partial monosomy 7). In some cases, several base pairs are abnormally deleted or duplicated in part of chromosome 7. A circular structure called ring chromosome 7 is also possible. Ring chromosomes occur when a chromosome breaks in two places and the ends of the chromosome arms fuse together to form a circular structure.

Cancers

Changes in chromosome 7 occur frequently in different types of cancers.  These changes are typically somatic, which means they are acquired during a person's lifetime and are present only in cancer cells.  Many forms of cancer are associated with damage to chromosome 7.  In particular, changes in this chromosome have been identified in cancers of blood-forming tissue (leukemias) and cancers of immune system cells (lymphomas).  A loss of part or all of one copy of chromosome 7 is common in people with myelodysplastic syndrome, which is a disease of the blood and bone marrow. People with this disorder have an increased risk of developing leukemia.

Studies suggest that some genes on chromosome 7 may play critical roles in controlling the growth and division of cells.  Without these genes, cells could grow and divide too quickly or in an uncontrolled way, resulting in a cancerous growth.  Researchers are working to identify the genes on chromosome 7 that are involved in the development and progression of cancer.

Additional Information & Resources

Additional NIH Resources

Scientific Articles on PubMed

References

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