Deep phenotyping to improve understanding of causal mechanisms and underlying gene mutations in primary lymphoedema and lymphatic malformations

Lymphoedema is swelling of any body part caused by a fault or obstruction in the lymphatic system, and is one of the most neglected areas in healthcare. Data suggest it is twice as common as type 1 diabetes (which is estimated at 400,000 in the UK) but much less recognised. Primary lymphoedema is often considered genetic in origin, whereas secondary lymphoedema has an identifiable cause such as the surgical removal of lymph glands for cancer. In the last 5 years a number of genes have been identified which, when faulty, cause inherited forms of lymphoedema. Finding the causal gene means a specific diagnosis can be made by a blood test through examination of the DNA of the patient suspected of having that particular type of lymphoedema. This helps inform the patient about their condition and what might happen to them in their lifetime. We have been studying lymphoedema for over 30 years. Genes have been discovered through investigating the DNA of patients who have as closely matched lymphoedema as it is possible to test. Detailed clinical histories and examination findings are recorded but clinical appearances alone are often not sufficient to distinguish one type of Primary Lymphoedema from another. This proposed research study is designed to provide better methods of investigation that will help distinguish one type of Primary Lymphoedema from another and give us a better insight into the mechanisms that produce the lymphoedema (and so help to design new treatments). Current tools for investigation of lymphoedema are very limited. Lymphoscintigraphy is the only widely available method within the NHS for the diagnosis of lymphoedema but it does not enable direct visualisation of the lymph vessels. Two methods are proposed to overcome this. The first is Magnetic Resonance Lymphangiography (MRL) using injected contrast, which enables distinction of lymph vessels from blood vessels. MRL will also be used to see the malformed lymph vessels inside the body. The second method of investigation is Indocyanine Green Lymphography (ICGL). This involves the injection of a dye that is seen by a camera in the near infrared spectrum wavelength of light. ICGL has been used to image lymph vessels just under the skin of an arm or leg prior to lymphatic microsurgery but has never been used to study Primary Lymphoedema. MRL will enable imaging of deeper lymph vessels whereas ICGL will provide information on lymph vessel pumping and valve function. Unlike lymphoscintigraphy neither MRL nor ICGL involve radiation. To study the smaller lymph capillaries in the skin we will perform biopsies but analyse them using a revolutionary, state of the art, 3D imaging technique. This will tell us much more about the structure and function of malfunctioning small lymphatic vessels in the patient groups. Infection can be a devastating consequence of lymphoedema because the lymph system is part of our immune system, so when the lymph system goes wrong so does immune function. We have already shown that in some genetic forms of lymphoedema, the white cells of the lymph system (lymphocytes) are low in number. There are virtually no studies in humans to explain why this is. We plan to study the numbers, trafficking and function of lymphocytes in order to understand if the immune dysfunction is a result of the genes or secondary to disturbed movement of the cells throughout the body from the lymphoedema. By developing improved investigation techniques we will be able to categorise our patients more clearly and discover more genes and how those genes make the lymph system grow and work. This may have relevance to diseases other than lymphoedema, which hitherto may not have been known to have a lymphatic contribution; for example the recovery of cardiac muscle after a heart attack may be dependent on lymphatic function. Discovering genes in primary lymphoedema will inform on their wide-ranging roles in human biology and pathology.