Management of Noonan Syndrome

Clinical Presentation and Diagnosis

The American College of Cardiology/American Heart Association guidelines identify patients with Noonan syndrome as having "short stature, webbed neck, hypertelorism, lymphedema, low-set ears and hairlines, hyperelastic skin, chest deformities, and micrognathia" in association with pulmonary stenosis 1
Pulmonary stenosis is the most common congenital heart defect in Noonan syndrome, occurring in approximately one-third of patients 1, 3
Characteristic dysmorphic features of Noonan syndrome include low-set ears, hypertelorism, and webbed neck 1, 2
Growth abnormalities, such as failure to thrive and proportionate short stature, are cardinal features of Noonan syndrome 2, 4

Immediate cardiology evaluation is critical because pulmonary stenosis in Noonan syndrome patients shows lower success rates with balloon valvuloplasty compared to isolated pulmonary stenosis 3
The American Heart Association recommends that children with structural heart defects receive coordinated multidisciplinary care through a medical home model 5
Cardiac catheterization may be necessary to assess the severity and determine optimal intervention timing, though echocardiography is typically the initial diagnostic modality 1, 3
Intervention is generally indicated when the resting gradient exceeds 40 mmHg, though patients with dysplastic valves may require surgical rather than catheter-based intervention 3

Genetic confirmation should occur concurrently with cardiac evaluation because Noonan syndrome is caused by mutations in PTPN11, SOS1, RAF1, RIT1, or other genes in the RAS/MAPK pathway 2, 4
Specific PTPN11 mutations confer an increased risk for various malignancies, including acute lymphoblastic leukemia, neuroblastoma, and rhabdomyosarcoma 4
Certain mutations carry a high risk for juvenile myelomonocytic leukemia, requiring surveillance with physical examination and complete blood count with differential every 3-6 months until age 5 years 4
Early genetic diagnosis enables appropriate cancer surveillance protocols and informs family planning 6, 4

Hematologic screening should be performed before any surgical intervention, as bleeding diathesis occurs in Noonan syndrome 2
Ophthalmologic evaluation should screen for ptosis, amblyopia, refractive errors, and strabismus 2
Audiologic assessment should evaluate for sensorineural hearing loss, which occurs in up to 40% of patients 2
Renal ultrasound should screen for structural renal anomalies 2
Developmental assessment should evaluate for learning difficulties and arrange early intervention services as needed 2