PID Patients Welcome to the Royal Free Hospital Primary Immunodeficiency Support Group. PID Patients was formed to represent the interests of patients with Primary Immunodeficiency (PID) who are managed by the UCL Centre for Adult PID. Helping patients There are over 150 known genetic defects that cause PID, all of these being rare and involving different parts of the immune system. The most common of all PIDs occurs in adults. Pioneering research With help and agreement from patients, research at the Royal Free investigates the fundamental causes of PID, the complications and the long-term management of these lifelong diseases. Fundraising Funding is needed to support our research in to PID at the Royal Free. News & events Keep up-to-date with the latest PID Patients news and events aimed at clinicians and patients. Contact us Find out how you can contact PID Patients and how you can become a member.