Pre-symptomatic testing in this context is where a genetic test is offered to an individual not known to have the condition (in this case diabetes) where another family member has previously been confirmed by molecular genetic testing to have a single genetic change causing their condition.
In the past there was little guidance for professionals regarding pre-symptomatic genetic tests for MODY, where diabetes may present in childhood. However, the benefit of learning about genetic results early on, allowing time to adapt to the news, has been demonstrated for some individuals. Each MODY family requesting pre-symptomatic testing should be considered individually with insight into their personal experience of diabetes and motivation for testing. At present, we recommend that families requesting pre-symptomatic tests are referred for genetic counselling to discuss the issues involved. This may be achieved most effectively by a trained Genetic Diabetes Nurse or in joint clinics involving both clinical genetics and diabetes teams. Families should be able to decide whether or not pre-symptomatic testing is appropriate for them after appropriate counselling.
If an adult wishes to have a pre-symptomatic test, the ethical issues are less complicated as they will be making an informed choice about their own health status. If they have reached adulthood without developing diabetes their chances of having a negative result are increased. If parents wish to have a pre-symptomatic test for their child the issues are more involved as the wishes of the parents need to be considered as well as the rights of the child. There are a number of issues which should be discussed during genetic counselling prior to a pre-symptomatic test and these can be found on our Diabetes Genes website.
There are other non genetic tests relating to specific types of MODY which may also be helpful for example individuals with a change in their HNF1A gene are likely to have a low renal threshold for glucose and some families may choose to dipstick urine for glucose as an alternative and if positive then progress for genetic testing at this point.
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