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]

Prophylaxis and the live-vaccine rule. The candidate explains that two medicines, taken every day for life, form the backbone of keeping their son safe between infections: an antibiotic (co-trimoxazole) that stops the bacterial cluster, and an antifungal (itraconazole or posaconazole) that stops the mould Aspergillus. The candidate states clearly that the live BCG vaccine — and other live bacterial vaccines — must not be given, because the weakened germ in the vaccine, which a healthy child clears, can persist and cause disease in their son. The candidate is honest that prophylaxis dramatically reduces but does not abolish the risk of infection, and that any fever or new symptom needs prompt assessment. [5] [12]

The curative option and the transplant decision. The candidate explains that there is a cure — a haematopoietic stem cell transplant, which replaces the defective immune cells with healthy ones from a donor — and cites the evidence honestly: the 712-patient multicentre study showed that 70 to 95 of every 100 children survived the transplant, with the best results when it is done before the infections have caused lasting organ damage and when there is a matched sibling donor. The candidate explains that the decision of when to transplant is individualised — some children do well for years on prophylaxis and defer, while children with frequent severe infection or troublesome inflammation benefit from earlier transplant — and offers to refer to the transplant centre for a full discussion and a sibling donor search. The candidate does not pressure but does not understate. [7]

The genetic implications, with empathy. The candidate explains that the condition is X-linked: the mother carries the gene on one of her X chromosomes, and each son has a one-in-two chance of being affected; each daughter has a one-in-two chance of being a carrier. The candidate anticipates and addresses the mother's guilt — she could not have known, she did not cause this, and carrier testing was not routinely available before her son's diagnosis — and offers carrier testing for the sister, maternal carrier counselling, and prenatal or preimplantation genetic diagnosis for future pregnancies. The candidate addresses the father's hope that antibiotics alone will suffice with honesty: prophylaxis is excellent and buys time, but it does not remove the long-term risk, and the transplant conversation is worth having now so the family is informed. [6] [12]

Communication skills assessed

The station assesses the candidate's ability to explain a complex genetic immunodeficiency in plain language without jargon, to use a clear structural framework, to anticipate and name the parents' emotional reactions (guilt, hope, fear) and address them with empathy rather than dismissal, to be honest about uncertainty and risk without overwhelming, and to close with a clear shared plan and a follow-up appointment. A candidate who hides behind jargon, who overstates or understates the transplant outcomes, or who fails to address the mother's guilt loses marks. [4] [7]