Incidental findings in genetic testing

When a medical test is performed in a patient for a particular purpose, it is possible that the test will identify an unexpected abnormality that is not related to the initial reason for doing the test. Such findings can be surprising to both patient and doctor. Such unexpected findings are sometimes called “incidental findings” because the outcome of the test is not related to the initial purpose for which the test was done.

Incidental findings are not new. They have always been a feature of medicine. For example, when a doctor examines a child with appendicitis, she may unexpectedly find that the child has a large liver which then requires further assessment.

Incidental findings in genetics

Incidental findings in genetics are particularly challenging because

• A mutation in one gene can result in a variety of diseases that are different from that in the index patient.
• A particular disorder may be caused by a mutation in any one of a number of different genes.
• Genetic tests often involve the analysis of a number of genes, and the consequence of an incidental finding may be different for each gene tested.
• Genetic tests for inherited mutations can identify the risk of developing disease in the future, either for the patient being tested or for relatives.

The potential significance of incidental findings will vary with different patients, doctors, tests, and situations. The possibility of incidental findings is best discussed by patient and doctor before a genetic test is done.

Incidental findings when testing one gene

If a genetic test involves just one gene, the discussion is usually straightforward. For each single-gene test listed on the Sonic Genetics website, we have provided links which provide further information about the gene and associated diseases which can inform such discussions.

Incidental findings when testing many genes

If a genetic test involves multiple genes (a “gene panel” test), it gets more complex as the significance of an incidental finding may vary with each gene.

On this website, you will find information about each gene included in our panels and the diseases it can cause. We have identified genes in which mutations can cause disease elsewhere in the body i.e. problems that are not obviously related to the reason the index patient was tested.

Incidental findings can carry implications for relatives and children, and so we have also indicated whether these “unexpected” diseases typically start in childhood or adulthood, and the part of the body that may be affected.

Please note that, even if a mutation is identified in a specific gene, an associated disorder is not necessarily likely to occur or to be untreatable.

We provide this supplementary information in good faith, but recognise that our list is not comprehensive; we have included links to further information should this be sought. Clinicians should not rely solely on the summary we have provided.

Incidental findings when examining every gene

It is now possible to examine all of a patient’s genes or the entire genome. This is referred to as “whole exome sequencing” (analysing all the protein-coding sequences in the patient’s genome) or “whole genome sequencing” (analysing all the coding and non-coding sequences in the patient’s genome). These large-scale analyses have an established role in research. They are also being used in some diagnostic work because it can be cheaper to analyse everything rather than analyse a subset of genes. However, such analyses are more likely to make incidental findings because thousands of genes have been analysed.