GOSH is a world-leading paediatric centre for the treatment of rare diseases, 75 per cent of which affect children. One in 17 people will suffer from a rare disease at some point in their lives, and 30 per cent of patients will die before their fifth birthday.
Read more about the patients featured in the episode, and the specialists who treat them, below, and find out how you can help.
At just three years old, Keano and his mum left their home in Zimbabwe to have treatment in the UK for his severe congenital neutropenia. Individuals with this rare condition lack neutrophils – a type of white blood cell in the bone marrow which fights infection – which makes them prone to recurrent infections.
Keano had a bone marrow transplant at GOSH after seven years of searching for a donor match.
Six-year-old Herb had a bone marrow transplant at GOSH after being diagnosed with a rare syndrome called NEMO deficiency, which affects his immune system.
Getting a final diagnosis was a lengthy process as Herb's disease is so rare.
Specialists also found Herb had a previously undocumented gene mutation, making his condition new territory for everyone involved.
Eleven-year-old Teigan was diagnosed with severe combined immunodeficiency (SCID) as a baby.
Using a pioneering treatment called gene therapy, specialists at GOSH have extracted Teigan's faulty genes and replaced them with working ones to treat her rare disease.
Paul has been Director of the Bone Marrow Transplant Unit at GOSH since 1994. He specialises in stem cell transplant for primary immunodeficiencies and reduced intensity stem cell transplant in paediatric diseases.
Paul is married to Dr Catherine M Owens, Consultant Radiologist at GOSH, and the couple have three children.
Bobby is an expert in paediatrics and immunology at GOSH and the UCL Institute of Child Health. His time is split between seeing patients in the hospital and developing new gene therapy treatments for complex diseases of the immune system in the laboratory.
Bobby has a wife and three daughters and likes taking on cycling challenges in his spare time.
Persis specialises in haematology and bone marrow transplant, working in the Bone Marrow Transplant Unit at GOSH.
He spends half of his time looking after children undergoing bone marrow transplant, and half of his time on research.
Outside of GOSH, Persis has a keen interest in astronomy and cricket. He is married to a children's book illustrator and has one daughter.
Kanchan came to GOSH in 1999 as a Registrar in Haemato-oncology.
She specialises in paediatric bone marrow transplant.
Married with two children, Kanchan's interests outside of work include Zumba, Indian music and cooking.