Noonan syndrome and RASopathies — branching viva

Opening question

A newborn on the postnatal ward has a Turner-like phenotype with a 46,XY karyotype and pulmonary valve stenosis. What is the unifying diagnosis, and why does the molecular confirmation strategy matter beyond the clinical label? [1] [2]

Branch 1 — the cardiac safeguard and the gene-cardiac link

Take the same child. What is the cardiac surveillance that must happen by six weeks, and why can hypertrophic cardiomyopathy be silent? Which gene variant is most strongly associated with HCM, and how does that change the surveillance intensity? [3] [1]

Branch 2 — the bleeding trap

At age five the child needs a dental extraction. The mother reports easy bruising. What coagulation abnormality is common in Noonan syndrome, and what must you do before the procedure? [1] [3]

Branch 3 — the RASopathy spectrum

A different infant presents with coarse features, deep palmar and plantar creases, severe feeding difficulty, failure to thrive, and hypertrophic cardiomyopathy. What syndrome is this, which gene is involved, and what additional tumour surveillance is required? [4] [1]

Closing — the pathway and the panel

In one sentence, why are these conditions called the RASopathies, and why is a multigene panel preferred over PTPN11 single-gene testing? [5] [2]