Noonan syndrome

Page most recently updated 7 September 2026

This page focuses on the reported psychiatric associations, which may be the initial presenting manifestation, and on other clinical features that may assist the psychiatrist or primary care physician in identifying the underlying diagnosis, considered through the lenses of the diagnostic lenses framework.

Noonan syndrome is a rare genetic disorder. It is genetically heterogeneous and can occur as an inherited or de novo genetic condition, with inheritance usually autosomal dominant, although rare autosomal recessive inheritance also occurs; absence of a relevant family history therefore does not exclude the diagnosis. The phenotype may resemble Turner syndrome, particularly in females, in its short stature, webbing of the neck, and congenital heart disease, but these conditions are genetically distinct. Noonan syndrome affects both females and males and is more characteristically associated with pulmonary valve stenosis and pectus deformities, whereas Turner syndrome is associated with a sex chromosome abnormality and more often has left-sided cardiac defects. A distinctive presentation of Noonan syndrome may include the combination of webbing of the neck, pectus excavatum, cryptorchidism, and pulmonary valve stenosis.

It can present with psychiatric features such as ADHD, anxiety, depression, behavioral dysregulation, and difficulties with attention and executive functioning. Social and communication difficulties may also occur. Cognitive impairment is generally mild when present, although learning difficulties and developmental delay are more common.

From a morphologic lens perspective, other features include (but are not limited to):

  • Low Posterior Hairline

  • Neck webbing

  • Short neck

  • Widely spaced eyes

  • Epicanthus

  • Downslanted palpebral fissures

  • Ptosis

  • Low-set ears

  • Increased posterior angulation of ears

  • Depressed nasal bridge

Other characteristic features include short stature, hypotonia, joint hypermobility, and skeletal abnormalities, particularly the characteristic pectus deformities. Cardiovascular manifestations are particularly important and include pulmonary valve stenosis and hypertrophic cardiomyopathy, as well as atrial septal defects and other congenital heart defects. Lymphatic abnormalities may include lymphedema and lymphatic dysplasia. Additional reported features include cryptorchidism in males, hearing impairment, ophthalmologic abnormalities, renal abnormalities, bleeding and coagulation abnormalities, feeding difficulties, and scoliosis.  

Early diagnosis is important to identify and monitor potentially serious cardiovascular, hematologic, lymphatic, renal, auditory, ophthalmologic, neurologic, and developmental complications, recognize neuropsychiatric needs early, and institute tailored multidisciplinary surveillance and treatment. In particular, bleeding or coagulation abnormalities should be considered before surgery or invasive procedures, while ongoing cardiac surveillance is recommended throughout life.

Selected references and further reading — Morphologic lens

Jones KL, Jones MC, del Campo M. Smith's recognizable patterns of human malformation. 8th ed. Philadelphia: Elsevier; 2021.

Reardon W. The bedside dysmorphologist: a guide to identifying and assessing congenital malformations. 2nd ed. Oxford: Oxford University Press; 2016.

Allanson JE, Biesecker LG, Carey JC, Hennekam RCM. Elements of morphology: introduction. Am J Med Genet A. 2009;149A(1):2-5. doi:10.1002/ajmg.a.32601.

Hennekam RCM, Biesecker LG, Allanson JE, Hall JG, Opitz JM, Temple IK, Carey JC; Elements of Morphology Consortium. Elements of morphology: general terms for congenital anomalies. Am J Med Genet A. 2013;161A(11):2726-2733. doi:10.1002/ajmg.a.36249.