Postzygotic activating PIK3CA variants cause several phenotypes within the PIK3CA-related overgrowth spectrum (PROS). Variant strength, mosaicism level, specific tissue involvement, and overlapping disorders are responsible for disease heterogeneity. Our comprehensive systematic review of more than 1,000 cases with PROS and PROS-like conditions shows that defining clear-cut genotype/phenotype correlations for all PROS entities is not possible. Few genotype/ phenotype are feasible, including by variants/domains interested, variant allele frequency. The application of a ten hotspots tailored first-tier approach will diagnose 70% of cases, reducing analytic costs, the subsequent molecular approach should include genes associated with vascular phenotypes to increase the diagnostic yield. Our findings will help guide clinicians in the challenging process of patients’ diagnosis and stratification. (By Professor Nicoletta Resta, https://jmg.bmj.com/content/early/2022/03/06/jmedgenet-2021-108093 )