1. SECTIONS:
2. preface & acknowledgements
3. genetics at a glance
4. contacts, support & testing
5. testing & pregnancy
6. newborn screening
7. cancer in the family
8. cardiovascular conditions
9. chromosomal conditions
10. clotting & bleeding conditions
11. cystic fibrosis
12. diabetes
13. fragile X syndrome and other causes of developmental delay
14. haemoglobinopathies
15. hereditary haemochromatosis
16. neurofibromatosis
17. neurological conditions
18. psychiatric conditions
19. genetics in practice
20. emerging genetic technologies
21. glossary

Familial colorectal cancer

 

The following information has been taken from the Australian Cancer Network (2006), Familial aspects
of bowel cancer: a guide for health professionals. http://www.cancer.org.au/healthprofessionals/
PrimaryCareResources.htm

 

1. The lifetime risk of colorectal cancer to age 75 years in the general population is 1 in 17 for men and
   1 in 26 for women.
2. Although colorectal cancer mainly affects people over the age of 50 years, it can occur at any age.
   There are about 12,600 new cases and 4,700 deaths each year.

 

Genetics

1. The causes of colorectal cancer are complex and involve interactions between environmental and genetic factors. Cancer develops as the result of a multi-step process involving genetic mutations in cells lining the colorectal wall. Most colorectal cancers arise from adenomatous polyps.
2. Between 2 to 5% of patients with colorectal cancer have inherited a mutated gene that predisposes them to colorectal cancer.
3. The types of colorectal cancer known to involve genetic susceptibility are familial adenomatous polyposis (FAP) including MUTYL–associated polyposis (MAP), and hereditary non-polyposis colorectal cancer (HNPCC). Table 1 summarises the genes known to be involved in genetic susceptibility to colorectal cancer.
4. Mutation searching for familial colorectal cancer gene mutation is an expensive and often lengthy process that can potentially produce `uninformative’ results (see Contacts, support and testing).
5. Sometimes a causative mutation cannot be found in a person with FAP or HNPCC. In this case, it cannot be presumed that a mutation is not present. Therefore 1° relatives should be considered to be at 50% (or 1 in 2) risk of having inherited a mutation and participate in a screening and prevention
   program according to national guidelines (see ‘Category 3 (potentially high risk)’)
6. Asymptomatic family members shown not to have the mutation causing cancer in the family on
   predictive testing, still have an average risk of developing colorectal cancer based on their age and should follow recommendations for population screening. However, they can be spared the intensive
   screening needed by someone who has/may have the mutation

 

Table 1

Genes in which mutations are known to be associated with an inherited predisposition to colorectal cancer and other sites

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