Abstract
Genomic ascertainment is the inversion of the traditional phenotype-first approach; with a "genome-first" approach, a cohort linked to electronic health records (EHR) undergoes germline sequencing (array, panel, exome, and genome) and deleterious variation of interest in a gene (or set of genes) are identified. Phenotype is then queried from the linked EHR and from call-back investigation and estimates of variant prevalence, disease penetrance, and phenotype can be determined. This should permit a better estimate of the full phenotypic spectrum, severity, and penetrance linked to a deleterious variant. For now, given the modest size, limited EHR, and age of participants in sequenced cohorts, genomic ascertainment approaches to investigate cancer in children and young adults will likely be restricted to descriptive studies and complement traditional phenotype-first work. Another issue is the ascertainment of the cohort itself: Participants need to survive long enough to enroll. Not accounting for this may lead to bias and incorrect estimates of variant prevalence. Adult-focused cohorts with EHR extending back into childhood, linked to cancer registries, and/or studies that permit recontact with participants may facilitate genomic ascertainment in pediatric cancer research. In summary, genomic ascertainment in pediatric primary brain cancer research remains largely untapped and merits further investigation.