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66 CB 1.3 GENETIC VARIATION
USING KNOWLEDGE OF GENETICS
Genetic Screening
Genetic screening can be used to prevent the onset of diseases, or to assure their early detection
and treatment.
Stomach cancer is the fifth most common form of cancer worldwide, and the third most common
cause of cancer deaths. One in 110 people will be diagnosed with stomach cancer during their
lifetime.
In New Zealand, Māori have rates of stomach cancer three times higher than that of patients of
European descent. This is caused by a mutation in the gene CDH1. Carriers of this mutated gene
have a 70% lifetime risk of developing stomach cancer, and female carriers have an additional
30-40% risk of developing breast cancer. The discovery of a mutation in the CDH1 gene by New
Zealand researchers in 1998 began with the McLeod whānau who had a significant history of
familial gastric cancer. It has been estimated that from 1950 until the research team’s discovery,
up to 50 members of the McLeod whānau had died from the disease.
Genetic testing for CDH1 mutations involves analysing a blood or saliva sample to detect changes
in the DNA sequence of the gene. This type of testing is recommended for all individuals with a
family history of stomach cancer. If a CDH1 mutation is identified, individuals may be advised to
undergo regular surveillance to monitor for the development of stomach cancer, or may choose
to undergo preventative surgery to remove the stomach before cancer develops.
Since the discovery of the mutation in 1998, and the development of genetic screening, testing
and resulting stomach-removal surgery, only two members of the McLeod whānau have died from
stomach cancer. Wider screening throughout the Māori community has identified 25 additional
whānau that carry the mutated CDH1 gene in New Zealand.
G G G
C C C C C C
C C C C C
C
C
T T T T
T
T
T T
A A
A A A A A
A
A
G G G
C C C C C C
C C ? C C
C
C
T T T T
T
T
T T
A A
A A A A A
A
A
Sequence Chromatogram of CDH1
Normal sequence
Mutated sequence
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