Identification of eight novel VEGFR-3 mutations in families with primary congenital lymphoedema.

P rimary lymphoedema is oedema that occurs as a consequence of a failure of lymph drainage and arises from an intrinsic abnormality of the lymphatic system. Familial lymphoedema usually segregates as an autosomal dominant trait with reported variable expression and reduced penetrance. 3 Primary lymphoedema can be classified according to age of onset, at birth as primary congenital lymphoedema (PCL) or Milroy disease (MIM 153100) or, more commonly, after puberty as Meige disease (MIM 153200). Lymphoedema may occur as part of a well recognised syndrome, where the genetic defect may or may not be known, for example in Turner or Noonan syndrome (MIM 163950). Lymphoedema can also occur in association with other clinical features—for example, pubertal onset autosomal dominant lymphoedema with distichiasis (LD; MIM 153400), which has been linked to 16q24.3. 6 The gene for LD has recently been identified as FOXC2 (MFH-1) (MIM 602402), a member of the forkhead/winged-helix family of transcription factors, and mutations within this gene have been identified in families with LD. We have previously reported linkage to 5q35.3 in one large American family and four British families with PCL. This has also been shown independently by two other groups. 12 Subsequent mutations were reported in the gene encoding the vascular endothelial growth factor receptor 3 (VEGFR-3, also known as FLT4; MIM 136352; GenBank X68203 and S66407), which resulted in defective VEGFR-3 tyrosine kinase activity and signalling, suggesting this was the cause of primary lymphoedema. 13 The VEGFR-3 gene is expressed in the lymphatic endothelium of adult tissues. Targeted disruption of Vegfr-3 in mice leads to embryonic death at day 9.5 owing to defective development of large blood vessels and cardiovascular failure. Moreover, cutaneous overexpression of its ligand, vascular endothelial growth factor C (VEGF-C), induces selective hyperplasia of the lymphatic vasculature. This prompted the suggestion that lymphatic growth may be induced by VEGF-C and mediated through VEGFR-3. In this report we describe 12 PCL families consistent with linkage to the 5q35.3 region and report eight novel mutations (G854S, A915P, C916W, G933R, R1041W, R1041Q, del F 1108, and P1137L), two of which each occur in two separate families. Seven of the mutations are missense mutations, as is the type of mutation found previously, and one is a deletion mutation, which has not so far been reported. 13 We have also found eight polymorphic variations (N149D, 507 G.T, T494A, Q890H, P954S, P1008L, R1146H, and R1324L). Because, as with all previously reported mutations, the eight mutations identified in this study lie in the region of VEGFR-3 encoding the tyrosine kinase domain, they are predicted to interfere with VEGFR-3 signalling.