Noonan syndrome and RASopathies — formative SAQs

SAQ 1 (10)

A newborn boy is noted on the postnatal ward to have a triangular face, hypertelorism, ptosis, low-set posteriorly rotated ears, a short webbed neck, and widely spaced nipples. The karyotype is 46,XY. An echocardiogram shows pulmonary valve stenosis with dysplastic leaflets. ^{[1] [3]}

a) Define the RASopathies and explain why Noonan syndrome is the prototypical member. State the most likely genetic basis and the appropriate confirmatory test. (3 marks) ^{[1] [2]}

b) Outline the newborn-period surveillance items, including the timing and rationale of the cardiac investigation. (3 marks) ^{[3] [1]}

c) State the coagulation abnormality that is common in Noonan syndrome and explain why it matters for this child's future management. (2 marks) ^{[1] [3]}

d) The parents ask about the recurrence risk for their next child. Both parents are clinically unaffected. State the recurrence risk and explain the reasoning. (2 marks) ^{[1] [3]}