Why does cystic fibrosis show that genes do not completely determine a person’s health?

Cystic fibrosis (CF) serves as a clear example that genes do not completely determine a person’s health, challenging the rigid perspective of biological determinism. While CF is a recessive disorder caused by mutations in the CFTR gene, individuals with the exact same genotype often exhibit remarkably different phenotypes.1

The manifestation of the disease varies significantly between patients: some experience early onset while others experience later onset, and the severity of symptoms—such as the degree of lung or kidney affliction—can range from mild to severe. These differences indicate that an individual's health is shaped by a complex interplay between their genetic background and environmental factors, such as diet.1

Ultimately, this demonstrates that genes are not destiny. Even when the genetic basis of a condition is well understood, the observable health outcomes are not fixed, reinforcing the ethical principle that human potential and well-being should not be restricted by deterministic assumptions about genetic inheritance.1