Deciding "what" to screen for and "when": The importance of natural history information.

Genomic medicine promises to leverage research on human genetic variation to improve health. As technology improves, our increasing ability to determine an individual's genomic sequence must be matched with increased understanding of underlying mechanisms of disease and how phenotypes arise because of genetic variation. Knowledge about the etiology of rare monogenic conditions can be leveraged for medical and public health purposes through diagnostic testing and predictive screening. However, policy decisions about the use of genetic and genomic analysis in a predictive setting must consider the penetrance and expressivity of each monogenic condition and how these factors influence the timing of genomic screening and its potential benefits and harms. This means that high-quality data are required on the nature of genetic diseases and how they impact human health across populations. The objective of this paper is to address the inherent challenges in determining the onset of symptoms for rare monogenic conditions and underscore the importance of curating natural history data. By elucidating the natural progression of rare monogenic conditions, we can optimize screening strategies and guide clinical decision-making. Detailed information about natural history is critical to understanding the optimal timing of population screening and subsequent intervention for any given condition.