Noonan syndrome can be caused by mutations in various genes. Most cases are autosomal dominant or due to sporadic (de novo) mutations.
Features
There is variation in the signs and symptoms of Noonan syndrome, depending on the underlying cause. Typical features include:
- Short stature
- Webbed neck
- Broad forehead
- Small chin and jaw (micrognathia)
- Ptosis (eyelid drooping)
- Hypertelorism (widely-spaced eyes)
- High-arched palate
- Downward-sloping palpebral fissures (the gaps between the lower and upper eyelid)
- Low set ears
- Widely-spaced nipples
Associated Conditions
- Congenital heart disease (e.g., pulmonary valve stenosis and hypertrophic cardiomyopathy)
- Cryptorchidism (undescended testes), which can lead to male infertility
- Mild learning disability
- Bleeding disorders
- Lymphoedema
- Juvenile myelomonocytic leukaemia
Management
Management is supportive and involves the multidisciplinary team.
Growth hormone therapy may be used to improve adult height.
Last updated December 2025
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