What are genes and how do they work?
A gene is a sequence of DNA that codes for a specific protein. Cells in our body have enzymes that read genes from the DNA and make all of the proteins the cell needs. DNA is like a cookbook, and all cells have the same cookbook. A gene is like a recipe, and the protein that the gene codes for is like the cooked meal. Different types of cells all contain the same DNA but use that DNA to make different types of proteins. For example, liver cells use genes to make proteins for bile production, while neurons in the brain use different genes in the same DNA to make neurotransmitters.
Some genes make proteins that tell cells when to divide and when to stop dividing. These are often the genes that are affected in cancer. In an adult, certain cells divide quickly and often, while other cells stop dividing. Skin cells, for example, continue to divide throughout life. Neurons, on the other hand, stop dividing or divide very slowly.
When a gene involved in cell division is disrupted – a mutation in the DNA – cells may begin to divide even when they shouldn’t. If an important cell division gene has a mutation, or if mutations in enough genes happen, cells can divide and grow unchecked. This is how cancer develops.
What is a genetic syndrome?
A genetic syndrome is a disease caused by a gene mutation. Genetic mutations may run in families, or they can happen in a person as a new, "de novo" mutation. DNA is inherited (passed down) from both parents, carried on twenty-three chromosomes from each parent, for a total of forty-six chromosomes. Two chromosomes are sex chromosomes, or "allosomes" – XX for women or XY for men. The remaining chromosomes are called "autosomes."
A genetic syndrome with a mutation in the DNA on an autosome is passed on in either an "autosomal dominant" or "autosomal recessive" pattern. An autosomal dominant syndrome needs only one parent's copy of the gene to harbor a mutation – that mutated gene is "dominant" over the normal gene. An example of this is the BRCA1 mutation causing breast cancer – if a woman inherited a BRCA1 mutation from her parent, she is at higher risk for breast cancer herself. Because only one copy of the mutated gene is needed, autosomal dominant genetic syndromes often affect many people in a given family.
On the other hand, an autosomal recessive syndrome requires both parents' DNA to have the mutated gene. If a person inherits the mutated gene from both parents, he/she is at risk of developing the syndrome. Because two copies of the mutated gene must be inherited, autosomal recessive diseases affect fewer members of a given family.
How does a genetic syndrome relate to cancer?
While there are many genetic syndromes, only a few genetic syndromes are linked to increased cancer risk. Most cancers are not related to genetic syndromes. Most cancers arise later in life, after decades of DNA damage that mutates critical genes over time.
Cancer-related genetic syndromes, on the other hand, affect a critical gene from the very beginning of life. These syndromes may then lead to cancer at a much earlier age. While many families have members with cancer in old age, families with cancer-related genetic syndromes have a pattern of cancer in children and/or younger adults.
The genes affected in these syndromes tend to play a role in cell division, cell growth, DNA damage recognition, and DNA damage repair. Many of these genes produce "tumor suppressor" proteins, whose normal function is to prevent uncontrolled division and growth. When tumor suppressor genes are damaged, cells gain the ability to divide unchecked, potentially forming tumors or cancer.
Genetic Syndromes Related to Cancer
Autosomal dominant syndromes
Gene: Associated Cancer(s)
Hereditary breast and ovarian cancer
Hereditary prostate cancer
Lynch syndrome/hereditary nonpolyposis colorectal cancer
Familial adenomatous polyposis
Von Hippel-Lindau syndrome
Costello syndrome/faciocutaeneoskeletal syndrome
Multiple Endocrine Neoplasias (autosomal dominant)
Gene: Associated Cancer(s)
Multiple Endocrine Neoplasia (MEN) 1
(for all MEN subtypes, see http://ghr.nlm.nih.gov/condition/multiple-endocrine-neoplasia)
Multiple Endocrine Neoplasia 2A
Multiple Endocrine Neoplasia 2B
Familial Medullary Thyroid Carcinoma
Multiple Endocrine Neoplasia 4
Autosomal Recessive Syndromes
Gene: Associated Cancer(s)
This table shows the most common genetic syndromes related to cancer. The National Institute of Health's Genetics Information page has lots of information about each syndrome mentioned above.
Resources for more information
Learn about genetic counseling and genetic testing.
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