This project focuses on primary lymphoedema (PL). PL is a chronic, debilitating pathology characterised by swelling, most commonly of the limbs, due to lymph accumulation. It affects about 1 million people in Europe. Current treatments are limited mostly to lymphatic drainage and surgery. There is no cure. Thus, there is an essential need for understanding the disease. This project's strength resides in a cohort of one thousand well-characterized PL patients collected by the host laboratory. Whole-exome sequencing has been performed for ~750 patients to identify and characterise (likely) disease-causing genetic alterations. Variants in the known genes account for less than one-third of the cases, allowing us to search for novel causes. Overall, this project contributes to elucidation of the mechanisms underlying the development of PL and paves the way for improved diagnosis and the development of innovative treatment options.