Explaining chronic granulomatous disease and the transplant decision — OSCE

Candidate brief

You are the paediatric registrar. The parents of a four-year-old boy with newly confirmed X-linked chronic granulomatous disease (CGD) have been told the diagnosis and are waiting to speak with you. The DHR assay showed a virtually absent oxidative burst and the gene panel confirmed a CYBB (gp91phox) mutation. The mother carries the gene and her brother died in childhood from recurrent infection. Explain to the parents, in plain language, what CGD is and why their son keeps getting these infections, what lifelong prophylaxis means and why the BCG vaccine must be avoided, what a transplant involves and when it might be offered, and the genetic implications for the family — and address the mother's guilt and the father's hope that antibiotics alone will be enough. ^{[4] [5]}

Examiner framework — what a strong answer covers

Explaining the disease and the organism cluster (plain language). The candidate translates the respiratory burst into an accessible image: the neutrophil is the body's first responder that swallows germs and kills them with a chemical "bleach" burst, and in their son the chemical that makes that bleach is missing. So the germs that carry their own bleach-destroying enzyme (catalase) — Staphylococcus, Serratia, Aspergillus — survive inside his cells, which is why he keeps getting abscesses and pneumonias caused by exactly those organisms. The germs that most children clear easily (like the streptococci) do not trouble him. The candidate names the disease, confirms it is genetic and X-linked, and explains that the normal neutrophil count is not reassuring — the cells are there, they just cannot finish the job. ^[4]