Inger Norlyk Sheyanth

1 Introduction Noonan syndrome (NS) is among the most common RASopathies, with an estimated prevalence of 1 in 1000–2500 live births (Roberts et al. 2013). The phenotype of NS is characterized by variable expressivity, including congenital heart defects (CHDs), lymphatic disease, dysmorphic features, and neurodevelopmental involvement (Tartaglia et al. 2010, 2002). NS is predominantly inherited in an autosomal dominant manner, although recessive forms are increasingly recognized.