Diabetes Genes

Overview (Predictive Testing)

There is little guidance for professionals requested to conduct predictive genetic tests for MODY, where diabetes may present in childhood and preventing or delaying the condition is not yet possible. However, the benefit of learning about genetic results early on, allowing time to adapt to the news, has been demonstrated for some individuals (Fanos, 1997; Shepherd, 2000). Each MODY family requesting predictive testing should be considered individually with insight into their personal experience of diabetes and motivation for testing. At present, we recommend that families requesting predictive tests are referred to clinical genetics services for counselling to discuss the issues involved. This may be achieved most effectively in the context of joint clinics involving both clinical genetics and diabetes teams. Families should be able to decide whether or not predictive testing is appropriate for them after appropriate counselling. If an adult wishes to have a predictive 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 predictive 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. The following issues should be discussed during genetic counselling prior to a predictive test:

  • The dominant inheritance of MODY; this should be discussed simply and illustrated by use of a pictorial family tree
  • The penetrance of MODY: i.e. we are unable to identify the age at which the diabetes will develop if the affected gene has been inherited. Although it would mean a 99.3% lifetime risk of developing diabetes, it is possible that the child could reach adulthood knowing they had inherited the affected gene but not yet have developed diabetes
  • The implications of a positive result including: possible concerns about ‘labelling’ or treating the child differently, possible effects on an individual’s self image, issues of blame relating to the affected parent, and the means and frequency of monitoring for the development of diabetes in the future
  • The implications of a negative result including: possible survivor effects, feelings of separation from other family members with diabetes, the fact that diabetes screening is no longer necessary, and whether they would feel confident to stop any diabetes monitoring
  • Possible future implications for insurance and job prospects
  • Motivation for predictive genetic testing, for example, wishing to reduce uncertainty and allow more time to adapt to the news
  • Families individual concerns or questions should be discussed
  • Families should be reassured that they could postpone a predictive test if they wished to and that diabetes screening could be arranged annually, as opposed to having a predictive test, if they preferred
  • Once they had the predictive test result it would be impossible to return to a status of ‘not knowing’
  • Consideration of whether the child, when older, may regret that the decision to have a predictive test had been taken for them.

These recommendations have been developed as a result of a PhD thesis investigating attitudes of patients and professionals to genetic testing in MODY and provide professionals with the first guidelines relating to the provision of genetic testing in MODY (Shepherd, 2000). Discussion of the areas outlined allow clarification of issues which are important to families whilst providing professionals with specific details regarding the possible implications of genetic tests in diabetes. If these guidelines are followed the possible negative consequences of genetic testing in MODY should be minimised.