Wendy Kohlmann,
M.S.
Genetics is frequently in the news
on television and radio and in magazines and newspapers.Researchers
are identifying new genes and learning more about how they work
and function. This research can provide many benefits to individuals
and families at risk for inherited diseases. However, keeping up
with these new developments and understanding what they mean for
you can be a bit overwhelming. To help you become more knowledgeable,
we present the first article of a 4-part series reviewing genes,
their roles in cancer, their inheritance, and genetic testing.
Genes are the set of instructions inside our cells that tell our
bodies how to grow and develop. Each of our estimated 50,000 to
80,000 genes is a recipe for a specific protein that our body ne
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eds. Our genes are organized into
larger structures called chromosomes. Each cell has 46 chromosomes
that are organized into pairs. One chromosome in each pair is inherited
from our Mom, the other is inherited from our Dad. Because we have
two copies of each chromosome, we also have two copies of each gene.
Our genetic material is made up of
DNA which is made up of a series of chemicals, called bases, arranged
in different sequences. Scientists abbreviate these chemicals as
A, T, G, and C. These letters make up the alphabet that spells out
the instructions in our genes. Different combinations of A, T, G,
and Cs will specify different proteins to be made by different genes.
Sometimes a change, or mutation, in the sequence
of the bases in a gene causes the gene to stop functioning properly.
Some mutations may be caused by factors in the environment; other
mutations happen by chance. The cause of a mutation cannot usually
be determined.
A mutation can affect the function
of a gene in the same way a misspelling can affect the meaning of
a sentence. Here is an example:
GENE: ATTAGCACTG
SENTENCE: It is raining, so please wear your coat.
GENE: ATTATCACTG
SENTENCE: It is raining, so please wear your goat.
In the same way changing letters can cause a sentence to no longer
make sense, changes in the sequence of a gene will cause the instruction
it encodes to not make sense in our bodies.
About 5-10% of colon cancers are caused by an inherited mutation.
One, such condition, if familial adenomatous polyposis (FAP). This
is associated with the development of numerous polyps, called adenomas,
in the colon. These polyps are benign, but there is a high risk
for these adenomas to become malignant. People with FAP may also
develop polyps in other parts of the digestive system, such as in
the stomach. Hereditary non-polyposis colon cancer (HNPCC) is another
genetic condition that is associated with an increased risk for
colon cancer. Though HNPCC is not associated with the development
of many colon polyps, people who have HNPCC have an increased risk
for colon and other cancers including those of the endometrium (lining
of the uterus), ovaries, small intestine, upper urinary tract and
stomach. Peutz-Jeghers syndrome (PJS) is a condition associated
with polyps called hamartomas. These are different from the polyps
that occur with FAP. For people with PJS, the hamartomas most commonly
develop in the small intestine, and they are less likely to become
cancerous, but sometimes they can cause obstructions and other problems
in the digestive system. Juvenile polyposis (JP) is another condition
associated with the development of polyps at a young age. More details
about PJS and JP are included in some of the other articles in this
issue of the newsletter.
These conditions and some other rare conditions
are all caused by genetic changes that put people at risk for
colon cancer or the development of polyps. In part 2 of this series
we will talk about the specific genes that cause these conditions
and how changes in these genes may increase cancer risk.
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