We were able to identify the KRAS c.35G>A, p.(Gly12Asp) variant in plasma as the molecular cause of the clinically confirmed overgrowth syndrome in a ten-year old girl, which could not be detected in the analysis of skin fibroblasts using our tissue workflow, which may be due to heterogeneity not depicted in the resected specimen. The gene discussed is KRAS; the disease is overgrowth syndrome.