Your DNA
The genetics of colon cancer
Colon cancer is caused by a combination of genetic and environmental factors. About a third of the risk (35 percent) of colon cancer is considered to be inherited. This calculation is derived from studies of twins. As identical twins have identical sets of genes, any differences that appear between them can be attributed to environmental causes. Other studies demonstrate that possessing certain variants or genetic risk markers can lead to an increased chance of developing colon cancer above the general population.
We test for common variants that meet our standards for having an established association with colon cancer. We do not test for rare hereditary colon cancer syndromes, such as those caused by mutations in single genes. Knowing if you have hereditary predisposition to develop colon cancer can enable you to be alert for symptoms, get screened regularly and make appropriate preventive lifestyle changes.
What we found for colon cancer
We looked at five places on your genome where a one-letter difference in the genetic code affects your odds of colon cancer. At each location, there are two markers, for a total of 10 possible risk markers. You have two of the 10 risk markers we looked for.
Colon cancer
- You:
- 4.1%
- Avg:
- 5%
Your genetic markers
|
Gene or location 
|
Risk marker
|
Your markers
|
Odds ratio
|
Source
|
|---|---|---|---|---|
|
CRAC1
|
T | C C | 1.0 | Nature Genetics, 2008 |
|
8q24
|
G | G T | 1.04 | Nature Genetics, 2007 |
|
EIF3H
|
C | A A | 1.0 | Nature Genetics, 2008 |
|
SMAD7
|
T | C T | 1.16 | Nature Genetics, 2007 |
|
11q23
|
C | A A | 1.0 | Nature Genetics, 2008 |
What it means
Everyone has some chance of developing colon cancer. Each risk marker increases your odds by a different amount — some a little, some a lot. The "odds ratio" column in the chart above shows their relative impact.
About genetic markers
More than 99 percent of our genetic code is identical from person to person. The remainder is unique among individuals and gives rise to our diversity. DNA, the chemical instructions that determine our genetic code, is inherited from our parents and is composed of four biochemical bases that are represented by the DNA alphabet: A, T, G and C.
SNPs, or single nucleotide polymorphisms, are one-letter variations in our DNA. Each SNP (pronounced "snip") consists of two markers or variants, one inherited from each of our parents, and each marker has two possible versions, a risk version and a non-risk version. For example, at a given SNP, the base A may be the risk marker and the base G may be the non-risk marker. At another SNP, G may be the risk marker and T the non-risk marker.
The SNPs included in your Navigenics risk estimate have been reliably shown to be associated with diseases, although it is not known exactly how they contribute to the conditions. The degree of genetic risk you inherit is related, in part, to how many risk markers you have residing at each SNP — none, one (from one parent) or two (one from each parent). Just because you may have one or even two risk markers does not mean that you will definitely develop a given health condition, but it can raise your risk, especially if other lifestyle or environmental risk factors are present.