FOXC2 and Distichiasis: FOXC2 encodes a regulatory transcription factor and plays a role in the development of the mesodermal mesenchyme.[22], [23] Mice with heterozygous Foxc2 deficiency uniformly display distichiasis and also exhibit hyperplasia, as well as incomplete valve formation in their lymphatic vessels.[24] Heterozygous FOXC2 loss-of-function mutations like those in our subjects have been found in a number of LDS subjects.[17], [25]-[31] These findings indicate that FOXC2 haploinsufficiency is the disease-causing mechanism of LDS.