Presymptomatic testing

Genetic testing in some late onset autosomal dominant
disorders can be used to predict the future health of a well
individual, sometimes many decades in advance of onset of
symptoms. For some conditions, such as Huntington disease,
having this knowledge does not currently alter medical
management or prognosis, whereas for others, such as familial
breast cancer, there are preventative options available. For adult
onset disorders, testing is usually offered to individuals above
the age of 18. For conditions where symptoms or preventative
options occur in late childhood, such as familial adenomatous
polyposis, children are involved in the testing decision.
Presymptomatic testing is most commonly done for individuals
at 50% risk of an autosomal dominant condition. Testing
someone at 25% is avoided wherever possible, as this could
disclose the status of the parent at 50% risk who may not want
to have this information. There are clear guidelines for
provision of genetic counselling for presymptomatic testing,
which include full discussion of the potential drawbacks of
testing (psychological, impact on the family and financial), with
ample opportunity for an individual to withdraw from testing
right up until disclosure of results, and a clear plan for follow up.