From Genetic Counseling in Individuals to Cascade Screening in Populations: An Emerging Role for Public Health Practice

There are more than 2500 diseases for which genetic testing is currently available. Most of these diseases are individually rare conditions but collectively affect millions of individuals and families worldwide. Genetic diseases are usually caused by mutations in one or a few genes that may confer a high risk of illness, disability and early death. Immediate relatives of affected people can be at highest risk for these diseases.   Rapid advances in genomics, including whole genome sequencing, are leading to more accurate diagnosis, early detection and carrier testing for these diseases.  Genetic counseling provides information for decision making by affected people and their families. 

In 2012, the CDC Office of Public Health Genomics developed a three tier evidence-based classification schema for genomic applications in public health and clinical settings. Our online table is intended to promote conversation and stimulate input from providers, public health practitioners and consumers alike.  The schema takes a population perspective for an emerging role  for public health programs to supplement clinical practice. Tier 1 includes applications supported by recommendations from evidence panels that used systematic reviews to assess the balance of benefits and harms from testing and interventions. In addition to newborn screening, which is the largest public health genetics program in the world, we highlight three tier 1 diseases-hereditary breast and ovarian cancer, Lynch syndrome and familial hypercholesterolemia as candidates for existing public health programs to identify people at increased genetic risk for disease through  “cascade genetic screening.”

Cascade screening is an active process to find relatives of persons affected with certain genetic conditions, for which interventions exist that that can save lives.  In the recent video, “Cascade genetic screening and public health practice: an idea whose time has come”, the case was made that 2 million people in the United States are affected with one of the three genetic conditions mentioned above. Existing public health programs at the federal and state levels (notably cancer and heart disease programs) can partner with clinical medicine and other stakeholders to develop policy, educational and surveillance-based interventions for these conditions. Since 2011, public health programs in hereditary breast and ovarian cancer have been under way in Michigan, Oregon and Georgia.

What about the role of public health for the vast majority of other genetic conditions, where cascade screening is not a tier 1 application?  For many individual rare disorders, there may never be sufficient evidence to meet the highest evidentiary criteria of major guideline-producing organizations using traditional evaluation methods.  Clearly, unbiased, accessible information about genetic conditions is important for affected individuals and their relatives. For example, CDC has developed and sponsored educational and informational programs around selected genetic conditions, such as Duchenne Muscular Dystrophy, Fragile X Syndrome, and Primary Immune Deficiency Disorders. Many community programs exist both within and outside the US, a field sometimes referred as Community Genetics.  Information could be  collected through the use of population based registries that could show impact of these programs at the individual, family and population levels.

We will continue to monitor the evolving scientific evidence to include more genetic conditions in tier 1 applications for population and/or family-based cascade screening programs. We invite our readers’ comments and input on what public health practice can do for individuals and families affected with genetic diseases.