Considerations in genetic testing

 

  1. Genetic testing has distinct advantages, disadvantages and limitations and should only be used after the person being tested has given full consideration to the relevant issues.
  2. Genetic conditions by their nature run in families, so that a diagnosis in one member has implications for other family members.
  3. Testing may benefit individuals and families in a number of ways but it may also create dilemmas which need sensitive management, making genetic counselling an essential element of genetic testing.
  4. All testing should be carried out with the informed consent of the person being tested.
  5. It is important for health professionals requesting tests and potential test users to become familiar with the context in which the tests are used.
  6. Mutation searching can be an expensive and lengthy process. The results can be complex and hard to interpret.
  7. A positive genetic test result means that a mutation has been found in the gene being tested. This result may confirm a diagnosis, confer a higher risk of developing a disease, or be an indication for further testing
  8. A negative genetic test result means that no mutation was found. However, the result is uninformative as it is possible that the genetic testing may not be sensitive enough to identify all the disease causing genetic mutations in that gene. This may occur in, for example, familial cancer mutation searching (not predictive testing for familial cancers) or where there are multiple different mutations in a gene such as in genetic testing for cystic fibrosis
  9. The test may find a gene change of unknown significance. This may be referred to in the laboratory report as ‘unclassified variant’, a ‘variant of unknown significance’ or a polymorphism. The test result is considered uninformative
  10. Predictive genetic testing involves testing for the known family-specific genetic mutation, so it usually results in a definitive positive or negative result for that mutation. It is less expensive and can be done in much less time than mutation searching.
  11. Pre-symptomatic testing of triplet repeat conditions can be done without the genetic testing of other family members.
  12. Genetic test results that are uninformative cannot confirm or rule out a diagnosis, or give any indication as to whether the individual has an increase risk of the condition (see Interpreting genetic test results).
  13. For example, in a condition such as Huntington disease where the result is provided as the number of triplet repeats detected in a specific part of the gene (see Neurological conditions), there is an intermediate range in the number of repeats where it is unclear if the person will develop the condition or not
  14. Residual risk may be present when no mutation is found (a ‘normal’ test result) where there are multiple known mutations in a gene if the panel of mutations tested for in that gene is limited, for example cystic fibrosis genetic testing in newborn screening (see Newborn screening)
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Pre- and post-test genetic counselling

  1. Testing should be accompanied by pre- and post-test genetic counselling that addresses:
  2. The genetic condition being tested including, where appropriate, clinical features, age of onset, pattern of inheritance, availability of treatment, genetic risk assessment
  3. Features or limitations of the laboratory test
  4. Details of the test, testing process, length of time to obtain test results
  5. Interpretation of results
  6. Implications of positive and negative results
  7. Options available on the outcome of testing
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