The first patient in the UK and Europe has received leniolisib, a newly licensed treatment for activated PI3-kinase delta syndrome (APDS).
Mary Catchpole's mother, grandmother and several other relatives died of APDS, which affects the immune system, reducing the ability to fight infections.
Mary's relatives were offered DNA sequencing at Addenbrooke's Hospital in Cambridge, where Mary was treated, which led to the discovery of a genetic variant as a cause for their immunodeficiency.
Dr Anita Chandra, consultant immunologist at Addenbrooke's Hospital and affiliated assistant professor at the University of Cambridge, said: 'It is incredible to go from the discovery of a new disease in Cambridge to a treatment being approved and offered on the NHS, within the space of 12 years.'
BBC News has more information.