Lymphatic malformation-1 (LMPHM1, OMIM #153100), also known as primary congenital lymphedema, is usually caused by heterozygous mutations in FLT4. In an LMPHM1 patient, Ghalamkarpour et al. reported a homozygous missense mutation (c.2563G.A; p.A855T) in FLT4 [81]. Here, FLT4 is linked to lymphatic malformation 1.