Genetic Syndromes

What are genes and how do they work?

Genes are made of DNA and inherited (passed down) from parents to their children. The study of genes is called “genetics.” It is thought that humans have about 20,000 to 25,000 genes. Some genes make proteins that tell cells when to divide and when to stop dividing. These genes are often the ones that are affected by cancer.

The different cells in our body can use DNA in different ways. For example, liver cells use genes to make proteins that make bile, while cells in the brain (called neurons) use different genes in the same DNA to make neurotransmitters (chemical messengers in your body).

When a gene that helps with cell division is damaged (called a mutation in the DNA), cells may begin to divide even when they shouldn’t. This kind of mutation causes cells to divide and grow unchecked and out of control, causing cancer.

What is a genetic syndrome?

A genetic syndrome is a disease or group of diseases caused by a gene mutation. Genetic mutations can be found in members of a family, or they can happen in a person as a new, "de novo" mutation. DNA is inherited from both parents, carried on 23 chromosomes from each parent, for a total of 46 chromosomes. Two chromosomes are sex chromosomes, or "allosomes" (XX for women or XY for men). All the other chromosomes are called "autosomes."

A genetic syndrome that has a mutation in the DNA on an autosome is passed down in either an "autosomal dominant" or "autosomal recessive" pattern.

• An autosomal dominant syndrome needs only one parent's DNA to have the mutated gene. This mutated gene is "dominant" over the normal gene.
  • An example of this is the BRCA1 mutation causing breast cancer. If you inherited a BRCA1 mutation from your parent, you are at higher risk for breast cancer. Because only one copy of the mutated gene is needed, autosomal dominant genetic syndromes often affect many people in the family.
• An autosomal recessive syndrome needs the DNA of both parents to have the mutated gene. If you inherit the mutated gene from both of your parents, you are at risk of having 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 affect my cancer risk?

There are many types of genetic syndromes, but only a few are linked to a higher cancer risk. Most cancers are not related to genetic syndromes. Most cancers happen later in life, after years of DNA damage that mutates genes over time.

Genetic syndromes that cause cancer affect that gene from the beginning of life. These syndromes may then lead to cancer at a much younger 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 make "tumor suppressor" proteins, whose normal job is to keep cells from dividing and growing out of control. When tumor suppressor genes are damaged, cells have the chance to divide and grow out of control, possibly forming tumors or cancer.

Genetic Syndromes Related to Cancer

(Table adapted from 1 Weitzel et al.)

Autosomal Dominant syndromes

Multiple Endocrine Neoplasias (autosomal dominant)

Autosomal Recessive Syndromes

This table shows the most common genetic syndromes related to cancer. The National Institute of Health's Genetics Information page has information about each syndrome mentioned above.

Resources for more information

Learn about genetic counseling and genetic testing.