A teenager from Norfolk has become the first patient in Europe to be given a newly licensed treatment which could potentially cure her life-threatening, inherited disorder.

Mary Catchpole, 19, lost her mother, grandmother and several other relatives to the rare condition which affects the immune system, reducing her ability to fight infections.

“This treatment has brought me hope and joy,” Mary told BBC News: “I feel like I can do anything, but it is bittersweet because my family members passed away before they could benefit.”

The newly licensed drug, leniolisib, is the first targeted treatment for her condition, Activated PI3-kinase Delta Syndrome or APDS.

Not only is Mary the first patient to benefit from the drug but her family played a key role in research leading to the discovery of the ultra-rare condition.

APDS was identified in 2013 by researchers at the University of Cambridge and clinicians at Addenbrooke’s hospital who found a faulty gene carried by several members of Mary’s family.

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.”

Mary’s father Jimmy said: “We just wanted to help, not just for our own sakes, but we’d heard there were other rare cases.

“My wife volunteered for trials and, when Mary got old enough, she did too.”

Mary’s mother Sarah died aged 43, her aunt aged 12, her uncle aged 39 and her grandmother at 48.

One of Mary’s cousins was successfully treated as a child with a bone marrow transplant, but these carry significant risks.

Mary, who was 12 when her mother died, told us: “It was always a fear that I would die young too but with this medication, I know I can have a longer life, which is what she wanted.”

In APDS, an enzyme produced in the body is “switched on” all the time, disrupting the development of white blood cells and causing the immune system to be disregulated.

People with the condition are vulnerable to repeated lung infections which can lead to irreversible damage. It can cause organs and lymph nodes to swell, and the body’s immune system to attack healthy tissue. Patients are also at risk of lymphoma, a cancer which affects a type of white blood cell.

The drug, branded Joenja, is taken twice daily as tablets, and works by blocking the enzyme, allowing the immune system to work normally.

Jimmy told the BBC: “This is something I have dreamt about since Mary was first diagnosed; it is giving her the chance to live a normal life.”

Mary suffered regular chest infections as a child and has been repeatedly treated with intravenous antibiotics, nebulisers and immunoglobulin replacement therapy.

She has been taking the leniolisib tablets for less than a month but has already stopped some other medication.

Dr Chandra, who is Mary’s consultant and has treated several other family members, said the drug was a “potential cure”.

Mary is rethinking about how she will live in future: “I want to go on more adventures and take risks because all I’ve ever known is medication, needles, and hospital appointments, whereas now I can find out who I truly am.”

The faulty gene is carried on the maternal line so there is a 50:50 chance it will be passed to affected women’s children.

Mary said she would like to become a dance teacher, while continuing her work as a teaching assistant. She said she had been cautious around people because of the risk of infection but no longer felt scared.

Prof Sergey Nejentsev from the University of Cambridge who led the research that discovered APDS said: “As soon as we understood the cause of APDS, we immediately realised that certain drugs could be used to inhibit the enzyme that is activated in these patients.

Leniolisib does precisely that. I am delighted that we finally have a treatment which will change the lives of APDS patients.”

Leniolisib has a list price of £352,000 a year, but was approved as cost effective by the health regulator NICE after the NHS negotiated a substantial, confidential discount.

NICE estimates the drug could benefit up to 50 patients over the age of 12 in England.

Prof James Palmer, NHS England’s Medical Director for Specialised Commissioning, said: “This treatment could be life-changing for those affected by this debilitating genetic disorder, and this important step forward is another example of the NHS’s commitment to offering access to innovative medicines for those living with rare conditions.”