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Noonan syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Noonan syndrome

Noonan syndrome is a genetic condition that affects many areas of the body, characterized by distinctive facial features, short stature, heart defects, and bleeding problems.

Overview

Noonan syndrome is part of a group of related conditions known as RASopathies. It is characterized by a wide range of signs and symptoms, including skeletal malformations, developmental delays, and an increased risk of certain cancers, such as leukemia.

Symptoms

  • Facial Features: Deep groove between the nose and mouth, pale blue or blue-green irises, and low-set, backward-rotated ears.
  • Growth: Short stature, often with slow growth over time due to abnormal growth hormone levels.
  • Heart Defects: Commonly includes pulmonary valve stenosis (narrowing of the valve controlling blood flow to the lungs) or hypertrophic cardiomyopathy.
  • Bleeding: Tendency for excessive bruising, nosebleeds, or prolonged bleeding after surgery.
  • Development: Most children have normal intelligence, though some may have intellectual disabilities or special educational needs.

Causes

Mutations in multiple genes, most commonly PTPN11, SOS1, RAF1, and RIT1, cause Noonan syndrome. These genes provide instructions for proteins in the RAS/MAPK cell signaling pathway. Mutations typically cause these proteins to remain active longer than normal, disrupting the regulation of cell growth, division, and movement.

Genes Associated with Noonan syndrome

  • BRAF, KRAS, LZTR1, MAP2K1, NRAS, PTPN11, RAF1, RIT1, SOS1

Inheritance

Noonan syndrome is inherited in an autosomal dominant pattern, meaning one copy of the altered gene in each cell is sufficient to cause the disorder.

Frequently Asked Questions

If a child shows sudden shortness of breath, fainting, chest pain, rapid heartbeat, or a new or worsening heart murmur, these are red flags that warrant immediate cardiology assessment. Early detection of conditions like pulmonary valve stenosis or hypertrophic cardiomyopathy can prevent complications such as heart failure or arrhythmias.
Regular monitoring of growth charts, a balanced diet rich in protein, calcium, and vitamin D, and discussion with a pediatric endocrinologist about growth hormone therapy are key. Growth hormone treatment is often considered when height percentiles fall below the 3rd percentile and growth velocity is low, after confirming no contraindications.
Schedule a pre‑test counseling session with a genetics professional to review family history, discuss potential outcomes, and obtain informed consent. Blood samples are typically drawn in the morning; fasting is not required, but avoid medications that may interfere with blood tests if advised.
Leukemia, particularly acute lymphoblastic leukemia, and certain solid tumors are slightly increased. Discuss with your oncologist about age‑appropriate screening, such as annual physical exams, blood counts, and, if indicated, imaging studies. Early detection improves outcomes.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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