Williams syndrome — branching viva

Outpatient clinic: an eight-month-old infant with failure to thrive, irritability, a distinctive facies with periorbital fullness and a stellate iris, a loud ejection systolic murmur radiating to the neck, and elevated four-limb blood pressure. The examiner asks: what is the unifying diagnosis and the chromosomal abnormality, which gene drives the cardiovascular phenotype, why does haploinsufficiency produce stenotic arteries, what is the first-line confirmatory test, and what is the cardiac surveillance obligation — then branches to the finding of hypercalcaemia and asks how you manage it, and finally to the question of whether the deletion is inherited and what that means for the family.