A Gene by Any Other Name
Inherited diseases run in families, but the pattern they show can vary widely. The utility of genetic testing reflects those differences.
What is meant by “inherited disease”?
Many common diseases, like diabetes, heart disease, cancer, and dementia, have genetic components. Most people with these diseases have a form caused by both genetic and lifestyle (or environmental) factors, called multifactorial inheritance.
There are other forms of inherited disease that are caused by single genes. Single-gene diseases have patterns of inheritance like dominant and recessive that may be recognizable from high school biology classes. Examples are conditions like sickle cell anemia, cystic fibrosis, or Huntington disease.
To make things more complex, sometimes even a subset of patients with common disease have a form that shows single gene inheritance; an example is maturity-onset diabetes of the young, or MODY.
Is there genetic testing for common diseases?
Most commercial genetic tests for conditions with multifactorial inheritance include one or a small number of genetic factors. These may sometimes even be important risk factors, just like having male gender is an important risk factor for heart disease. However, just as there are many other factors that influence a man’s risk for heart disease, there are many other genetic risk factors for common disease. Patients and their physicians need to be cautious about relying too much on this limited data because there may be other factors that science has not yet identified.
Advances with genetic testing are emerging because of computing technology to allow polygenic risk scores (PRS.) The idea behind a PRS is to take a more comprehensive approach to the interpretation of the genetic risk factors. Caution is important because many of these PRSs have not been validated in the general population.
Does that mean genetic testing is not useful?
No, absolutely not, many genetic tests for single-gene disorders provide very clear information about who in a family is at risk and who is not. It’s important to assess the inheritance pattern for the disease of interest before ordering genetic testing, Also, some PRSs have been validated, and a physician might use this risk information in forming a patient care plan.