Of the 227 patients seen in 2016, 17% (n=39) had lymphoedema associated with vascular malformations and/or segmental overgrowth (or undergrowth) (figure 2, pie chart) in comparison with 15% in 2010.8 It has been shown that postzygotic, gain of function mutations in PIK3CA may be responsible for many of the mosaic segmental overgrowth spectrum disorders.11 Postzygotic mutations are rarely identified in blood samples and therefore require a skin biopsy of the affected region. The gene discussed is PIK3CA; the disease is vascular malformation.