Noonan syndrome is associated with various changes, including striking facies with low-lying ears that are rotated towards the back, hypertelorism, ocular ptosis, a broad neck, and a low hairline. In addition, there may also be proportionate dwarfism, congenital heart defects (particularly pulmonary stenosis, hypertrophic cardiomyopathy), thoracic deformity, skin and hair changes, vision problems, cryptorchidism, learning disabilities, and a bleeding tendency.
The risk of cancer in children with NS is around 8 times higher. The cancer spectrum lists the following types of cancer (excerpt): Gliomas, such as dysembryoplastic neuroepithelial tumors, acute lymphoblastic leukemia, neuroblastoma, rhabdomyosarcoma
Specific mutations in PTPN11 (especially, but not exclusively, codon 61 or T73I) or KRAS (T58I) are associated with an increased risk of polyclonal, often transient myeloproliferative disorders during the first few months of life. These myeloproliferative disorders sometimes progress aggressively, and therapy is indicated.
Besides the changes typical of Noonan syndrome, darkly pigmented skin and ectodermal abnormalities can also be identified in people with NSLAH.
People suffering from NSML exhibit a Noonan syndrome phenotype and multiple lentigines, often accompanied by hypertrophic cardiomyopathy and a hearing impairment.
Noonan syndrome-like CBLS has a variable phenotype characterized by vasculitis, mild changes reminiscent of Noonan syndrome, and a high risk of juvenile myelomonocytic leukemia (JMML).