Noonan syndrome

Disease Description (Causes and Symptoms)

• Definition summary: Noonan syndrome is a genetic disorder accompanied by congenital malformations, characteristic facial features, and heart defects, with highly variable clinical manifestations.
• Cause/genetics: Mainly follows an autosomal dominant inheritance pattern. In many cases, it occurs due to a mutation without a family history. Pathogenic variants in genes related to the Ras–MAPK signaling pathway (e.g., PTPN11, SOS1, RAF1, KRAS, NRAS, RIT1) have been reported as causes.
• Pathophysiology: Overactivation of the Ras–MAPK signaling pathway affects cell proliferation, differentiation, and development, resulting in systemic developmental abnormalities and organ malformations.
• Main symptoms (frequency/features)
  • Facial features: Hypertelorism, ptosis, a broad forehead and small jaw, abnormally positioned ears, etc.
  • Heart: Congenital heart defects (approximately 60–70%), particularly pulmonary valve stenosis and hypertrophic cardiomyopathy (20–30%)
  • Growth and development: Normal at birth but growth delay and short stature (short stature during adolescence in 50–70%), developmental delay and learning disabilities (including mild intellectual disability)
  • Genitals: Cryptorchidism in boys (60–80%)
  • Eyes (approximately 95%): Strabismus, refractive errors (myopia and hyperopia), ptosis, etc.
  • Bleeding and coagulation abnormalities, lymphatic abnormalities (edema during the neonatal period), hearing problems, and skin, dental, and musculoskeletal abnormalities, etc.
  • Other: Growth hormone deficiency (approximately 45%), and rarely, an increased risk of leukemia
• Epidemiology: Reported in approximately 1 in 1,000–2,500 newborns (frequency varies among statistics).

Treatment Methods

• Principles: There is no curative treatment, and a multidisciplinary approach by specialists according to symptoms (medical genetics, pediatric endocrinology, pediatric cardiology, ophthalmology, otolaryngology, orthopedics, surgery, rehabilitation, etc.) is required.
• Cardiac-related
  • Pulmonary valve stenosis: Catheter balloon valvuloplasty or surgical treatment may be considered for moderate or more severe cases.
  • Hypertrophic cardiomyopathy: Drug treatment (beta blockers, calcium channel blockers, etc.); in severe cases, surgical or mechanical treatment or heart failure management
  • Regular follow-up with echocardiography and electrocardiography is recommended.
• Growth-related
  • Growth hormone treatment: Has been reported to be effective in patients with short stature and may be administered after evaluation (monitoring of effectiveness and adverse effects is necessary).
• Surgical treatment
  • Early correction of cryptorchidism (to reduce the risk of infertility and cancer), correction of ptosis, and surgery for thoracic or spinal deformities, etc., are performed when necessary.
• Developmental and functional treatment
  • Early intervention (speech therapy, physical therapy, occupational therapy, special education, etc.)
• Bleeding and coagulation management
  • Assessment of bleeding risk before surgery (including coagulation tests and platelet function tests) and preparation for blood therapy when necessary
• Other
  • Hearing aids and auditory rehabilitation for hearing impairment, thyroid hormone replacement for hypothyroidism, etc.
• Long-term monitoring: Regular monitoring of growth and cardiac, endocrine, hearing, and developmental status

Checklist Before an Outpatient Visit (Including Example Questions)

• Items to prepare and things to check
  • A list of currently taken medications (including dosage and frequency)
  • History of major surgeries and anesthesia
  • Previous echocardiography, electrocardiography, and genetic test results (the originals or summaries, if available)
  • Recent growth chart (height and weight) and developmental assessment results (language and cognitive assessments)
  • History of bleeding (frequent bruising, nosebleeds, bleeding during surgery) and family history (similar symptoms or genetic variants)
  • Hearing test and ophthalmologic findings (eye examination results)
• Information that is useful to explain to the doctor in advance during the outpatient visit
  • When symptoms began and how they have progressed (e.g., age when poor growth began and whether cardiac symptoms have worsened)
  • Changes in sleep, feeding, and eating status, exercise ability, and learning status
• Example questions (patients and caregivers can use these directly during the outpatient visit)
  • "Are there any items among the test results obtained so far that require attention?"
  • "How often should this patient's cardiac status (based on echocardiography and electrocardiography) be monitored?"

General Example Questions to Ask the Doctor

• What are the expected benefits and possible side effects of this medication (or treatment)?
• Is growth hormone treatment recommended for me (or my child)? What are the expected growth effects and follow-up plan?
• Are there any special points to consider during surgery (such as bleeding risk and anesthesia risk)?
• What should be kept in mind in daily life going forward (such as exercise and school activities)?
• Is there the same genetic risk for family members, and do you recommend family testing? How can genetic counseling be obtained?

Examples of Condition-Specific Questions

• Genetics and family-related
  • "Which gene (e.g., PTPN11 or SOS1) contains the variant identified in the test? How does this variant affect the prognosis or risk of complications?"
  • "Do you recommend genetic testing for my parents and siblings? How should the recurrence risk during pregnancy and childbirth be explained?"
• Treatment and procedure-related
  • "If heart surgery or balloon valvuloplasty is performed, are additional tests needed because of coagulation abnormalities? How should preparations be made before surgery?"
  • "What tests should be performed before, during, and after starting growth hormone treatment, and how often (echocardiography, IGF-1, blood glucose, etc.)?"