Williams syndrome — formative SAQs

SAQ 1 (10 marks)

An eight-month-old infant is referred for failure to thrive, persistent irritability, and chronic constipation. On examination she has a distinctive facies with periorbital fullness and a stellate iris, a loud harsh ejection systolic murmur radiating to the neck, and a four-limb blood pressure that is elevated. Serum calcium is markedly raised. ^{[1] [5]}

a) Give the unifying molecular diagnosis and name the chromosomal abnormality, the key gene responsible for the cardiovascular findings, and the first-line confirmatory laboratory test. (3 marks) ^{[2] [5]}

b) Explain why haploinsufficiency of this gene produces stenotic arteries rather than aneurysms, and name the two coronary and outflow consequences that most threaten this child's life. (3 marks) ^{[3] [5]}

c) Outline the immediate and ongoing management of her infantile hypercalcaemia, naming four interventions. (2 marks) ^{[6] [1]}

d) State the inheritance pattern and the recurrence risk in a future pregnancy if a parent is found to carry the deletion, and outline the cardiac surveillance obligation. (2 marks) ^{[1] [3]}