chromosome 7
Humans normally have forty six chromosomes in each cell, divided into twenty three pairs. Two copies of chromosome 7, one copy inherited from each parent, form one of the pairs. Chromosome seven spans about one hundred fifty nine million DNA building blocks (base pairs) and represents more than five 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 seven likely contains nine hundred to 1,000 genes that provide instructions for making proteins. These proteins perform a multitude of different roles in the figure.
Related Information
Health Conditions Related to Chromosomal Switches
The following chromosomal conditions are associated with switches in the structure or number of copies of chromosome 7.
7q11.23 duplication syndrome
7q11.23 duplication syndrome, a condition that can cause a diversity of neurological and behavioral problems as well as other abnormalities, results from 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 different disorder called Williams syndrome (described below), also known as Williams-Beuren syndrome. The region, which is 1.Five to 1.8 million DNA base pairs (Mb) in length, includes twenty six to twenty eight genes.
Extra copies of several of these genes likely contribute to the characteristic features of 7q11.23 duplication syndrome. Researchers are studying genes whose functions suggest that they might be related to particular features.
cancers
Switches in the number or structure of chromosome seven occur frequently in human cancers. These switches are typically somatic, which means they are acquired during a person’s lifetime and are present only in tumor cells. Many forms of cancer are associated with harm to chromosome 7. In particular, switches 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 seven is common in myelodysplastic syndrome, which is a disease of the blood and bone marrow. People with this disorder have an enhanced risk of developing leukemia.
Studies suggest that some genes on chromosome seven 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 tumor. Researchers are working to identify the genes on chromosome seven that are involved in the development and progression of cancer.
FOXP2-related speech and language disorder
Several different switches affecting chromosome seven can result in FOXP2 -related speech and language disorder. These switches involve a region of the long (q) arm of chromosome seven containing the FOXP2 gene. FOXP2 -related speech and language disorder is an uncommon condition that affects the development of speech and language commencing in early childhood. In some affected individuals, problems with speech and language are the only features of the condition. Other individuals also have delayed development of motor abilities such as walking and tying shoelaces, and autism spectrum disorders, which are conditions characterized by impaired communication and social interaction.
All of the genetic switches that underlie FOXP2 -related speech and language disorder disrupt the activity of FOXP2 , a critical gene for normal speech and language development. Some individuals with FOXP2 -related speech and language disorder have a deletion that eliminates a petite segment of chromosome 7, including the FOXP2 gene and several neighboring genes. Other people with this condition have a mutation within the FOXP2 gene itself. Less commonly, FOXP2 -related speech and language disorder results from a rearrangement of the structure of chromosome seven (such as a translocation) or from inheriting two copies of chromosome seven from the mother instead of one from each parent (a phenomenon called maternal uniparental disomy or maternal UPD, which is described in more detail with Russell-Silver syndrome, below). It remains unclear how having two maternal copies of chromosome seven affects the activity of the FOXP2 gene.
Extra features that are sometimes associated with FOXP2 -related speech and language disorder, including delayed motor development and autism spectrum disorders, likely result from switches to other genes on chromosome 7. For example, in affected individuals with a deletion involving chromosome 7, a loss of FOXP2 is thought to disrupt speech and language development, while the loss of nearby genes accounts for other signs and symptoms. People with maternal UPD for chromosome seven have FOXP2 -related speech and language disorder as part of a larger condition called Russell-Silver syndrome (described below).
Greig cephalopolysyndactyly syndrome
Abnormalities of chromosome seven are responsible for some cases of Greig cephalopolysyndactyly syndrome, a disorder that affects development of the limbs, head, and face. These chromosomal switches involve a region of the brief (p) arm of chromosome seven that contains the GLI3 gene. This gene plays an significant 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 inbetween chromosome seven and another chromosome. Other cases are caused by the deletion of several genes, including GLI3 , from the brief arm of chromosome 7. The loss of numerous genes can cause a more severe form of this disorder called Greig cephalopolysyndactyly contiguous gene deletion syndrome. People with this form of the disorder have characteristic developmental problems involving the limbs, head, and face, along with seizures, developmental delay, and intellectual disability.
Russell-Silver syndrome
Abnormalities involving the inheritance of chromosome seven can cause Russell-Silver syndrome, a infrequent condition characterized by slow growth, distinctive facial features, delayed development, speech and language problems, and learning disabilities.
People normally inherit one copy of each chromosome from their mother and one copy from their father. For most genes, both copies are voiced, or “turned on,” in cells. For some genes, however, only the copy inherited from a person’s father (the paternal copy) is voiced. For other genes, only the copy inherited from a person’s mother (the maternal copy) is voiced. These parent-specific differences in gene expression are caused by a phenomenon called genomic imprinting. Chromosome seven contains a group of genes that normally go through genomic imprinting; some of these genes are active only on the maternal copy, while others are active only on the paternal copy.
In seven percent to ten percent of cases of Russell-Silver syndrome, people inherit both copies of chromosome seven from their mother (maternal UPD) instead of one copy from each parent. Maternal UPD causes people to have two active copies of some imprinted genes and no active copies of others. An imbalance in active maternal and paternal genes on chromosome seven underlies the signs and symptoms of the disorder in these cases.
Saethre-Chotzen syndrome
Abnormalities of chromosome seven cause some cases of Saethre-Chotzen syndrome. This uncommon condition is characterized by the premature fusion of certain skull bones (craniosynostosis), which prevents the skull from growing normally and affects the form of the head and face. The chromosomal switches involve a region of the brief (p) arm of chromosome seven that contains the TWIST1 gene. This gene plays an significant role in early development of the head, face, and limbs.
The chromosome abnormalities responsible for Saethre-Chotzen syndrome include translocations of genetic material inbetween chromosome seven and another chromosome, a rearrangement of genetic material within chromosome seven (an inversion), or the formation of an abnormal circular structure called a ring chromosome 7. Ring chromosomes occur when a chromosome violates in two places and the completes of the chromosome arms fuse together to form a circular structure. Each of these chromosomal switches 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 mutation within the TWIST1 gene, affected children are much more likely to have intellectual disability, developmental delay, and learning difficulties. These features are typically not seen in classic cases of Saethre-Chotzen syndrome. Researchers believe that a loss of other genes on the brief arm of chromosome seven may be responsible for these extra features.
Williams syndrome
Williams syndrome is caused by the deletion of genetic material from the Williams-Beuren critical region (described above). Researchers believe that the characteristic features of Williams syndrome, which include mild to moderate intellectual disability or learning problems, unique personality characteristics, distinctive facial features, and heart and blood vessel (cardiovascular) problems, are very likely related to the loss of several of the genes in this region.
While a few of the specific genes related to Williams syndrome have been identified, the relationship inbetween most of the genes in the deleted region and the signs and symptoms of Williams syndrome is under investigation or unknown.
other chromosomal conditions
Other switches in the number or structure of chromosome seven can cause delayed growth and development, intellectual disability, distinctive facial features, skeletal abnormalities, delayed speech, and other medical problems. Switches in chromosome seven 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 DNA building blocks (nucleotides) are abnormally deleted or duplicated in part of chromosome 7. A circular structure called ring chromosome seven is also possible.
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