Noonan Syndrome

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Original Editor - User Kirenga Bamurange Liliane
Top Contributors - Kirenga Bamurange Liliane, Lucinda hampton, Chelsea Mclene, Naomi O'Reilly, Kim Jackson, Rucha Gadgil and Leana Louw

Definition

Noonan Syndrome (NS) is an autosomal dominant condition or a genetic mutation that prevents the normal development of different parts of the body. Noonan Syndrome is a genetic condition that affects people in so many ways including:

• distinctive facial features such as broad or webbed neck, drooping eyelids and a wider-than-usual distance between the eyes
• heath problems such as short stature
• chest deformity,
• congenital heart disease
• pulmonary stenosis,
• physical problems
• and possible developmental delays

The eponym “Noonan syndrome” was adopted in recognition of Dr. Jacqueline Noonan who was the first to indicate that this condition occurs in both genders, was associated with normal chromosomes, included congenital heart defects, and could be familial.

Dr. Jacqueline Noonan was the first doctor to study this condition was associated with and noticed that it affects both genders

Causes

The Noonan Syndrome is caused by a mutation of a gene or a faulty gene that is usually inherited from one of the parents. The most commonly altered genes are:

• the PTPN11 gene
• the SOS1 gene
• the RIFT1 gene
• the KRAS

Even though the symptoms are usually the same for all different genes, two of them are associated to specific conditions.

The faulty PTPN11 gene is commonly associated with pulmonary stenosis characterized by a narrowed heart valve and the faulty RAF1 gene, associated with cardiomyopathy which is a disease of the heart muscle.

Epidemiology / Pathological Process

The condition is present from before birth, although milder cases may not be diagnosed until a child gets older. It has a prevalence estimated at 1 in 1000 to 1 in 2500 live births.

Clinical Presentation

NS is most often characterized by facial and musculoskeletal features.  Although these features are more present during early childhood, they change over the time and appear less characteristic during adulthood:

• In the newborn infant, the head is large with a small face, a tall forehead, wide-spaced eyes, short nose, low set ears, and a broad or webbed neck
• Pectus deformity of the chest with pectus carinatum (protrusion of sternum an rib) and pectus excavatum (hollow chest)
• Kyphosis
• Scoliosis
• Cubitus valgus (outward deviation of the elbows)
• Rounded shoulders
• Rib abnormalities
• Genu valgum ( Knock knees)

Many infants with NS also have heart (cardiac) defects such as

• Pulmonary valvular stenosis
• Hypertrophic cardiomyopathy
• Septal defects

Individuals with NS may also present less common problems including:

• Leaning disability: children with NS tend to often have a mild learning disability due to a lower IQ average
• Feeding problems: children with NS may have problems with sucking and chewing
• Speech problems: articulation difficulty due to a high arched palate and weak muscles
• behavioral problems: some children with NS may have attention problems or difficulty to describe their or people emotions
• Eyes condition such as squint, lazy eye, astigmatation
• Hearing loss
• Hypotonia: decreased muscle tone will make children with NS reach early milestones later compared to other children
• Undescended testicles: one or or both testicles may fail to drop into the scrotum in boys with NS
• Infertitility can be ddiagnose in boys if undescended testicles are not corrected at an early age
• Lymphoedema
• Bone marrow problems
• Skin problems such as Dystrophic nails; Extra prominence on pads of fingers and toes; Follicular keratosis; Hyperelastic skin; Moles

Diagnostic Procedures

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Outcome Measures

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Management / Interventions

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Differential Diagnosis

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Resources

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