Frailty in mouse ageing: A conceptual approach.

Human life expectancy has increased dramatically in the last century and as a result also the prevalence of a variety of age-related diseases and syndromes. One such syndrome is frailty, which is defined as a combination of organ dysfunctions leading to increased vulnerability to adverse health outcomes. In humans, frailty is associated with various biomarkers of ageing and predicts relevant outcomes such as responses to therapies and progression of health status and mortality. Moreover, it is relatively easy to assess. To foster translation of mechanistic understanding of the ageing process and, importantly, of interventions that may extend healthy lifespan, frailty scales have been reverse translated into mice in recent years. We will review these approaches with a view to identify what is known and what is not known at present about their validity, reproducibility and reliability with a focus on the potential for further improvement.