Klinefelter syndrome and sex chromosome aneuploidy — branching viva

Outpatient clinic: a tall, shy fourteen-year-old boy with small firm testes, gynaecomastia, delayed puberty, and a history of language delay and learning difficulties. The examiner asks: how do you confirm the diagnosis, what is the mechanism and why does the extra X produce this phenotype, what is the endocrine and neurodevelopmental trajectory — then branches to the same patient at twenty-five presenting with a deep vein thrombosis, and finally to a prenatal counselling scenario after cell-free DNA flags a sex chromosome aneuploidy.