English: Clinical phenotyping together with genotyping have led to the division of patients with a primary lymphatic anomaly into five main groups, which are shown here as color-coded sections together with their various clinical sub-types of disease. This demonstrates that primary lymphedema is a complex heterogeneous condition for which several causal genes have been identified. Primary lymphedema is the major clinical feature in the green, pink and purple sections, whilst in the blue section lymphedema is not the dominant phenotypic feature. Phenotypes within the yellow section are thought to be caused by postzygotic mosaic mutations. Gene names (text in red italics) indicate the most likely molecular diagnosis for each subgroup, and in some cases, an alternative diagnosis is offered (gene names to “consider”). Only gene names included in this review are presented in this simplified version of the algorithm, for a comprehensive list of genes check the most current St. George’s classification algorithm in (https://pubmed.ncbi.nlm.nih.gov/32409509/). The indicated genes do not always explain the cause of disease in all patients in each group. For example, only 70% of Milroy disease patients are explained by mutations in FLT4/VEGFR3 (https://pubmed.ncbi.nlm.nih.gov/19002718/). FH, family history; +ve, positive; -ve, negative; y, year. ORPHA, phenotype number from www.orpha.net. (Image “St George’s Classification Algorithm” shared by St George’s Lymphovascular Research Group under the CC BY-SA-4.0 International license; https://commons.wikimedia.org/wiki/File:St_Georges_Classification_Algorithm.jpg).