Noonan syndrome is an autosomal dominant condition with multiple congenital anomalies that result in a characteristic phenotype, especially in newborns and young children.
Inheritance: autosomal dominant
Frequency: estimates vary based on severity, with clinical cases having a frequency of 1 in 1,000 to 1 in 2,500.
(1) short stature
(2) congenital heart disease (including pulmonary valve stenosis, hypertrophic cardiomyopathy, ASD, VSD)
(3) broad or webbed neck, may be edematous
(4) chest deformity with pectus carinatum ("keel-like" from a prominent sternum) superiorly and pectus excavatum (depression of the sternum) inferiorly
(5) cryptorchidism (in males)
(6) characteristic facies (see below)
(7) variable developmental delay
(8) widely spaced nipples
(9) variable lymphatics dysplasia, which may be associated with edema of the extremities or neck or with cystic hygroma
(10) prominence of the trapezius muscles
(11) variable coagulopathy
The facial proportions change as the child ages. The characteristic facies may be best identified in the neonate or young child. Past photographs of the patient, siblings and parents may be helpful.
Facial features in neonate:
(1) tall forehead
(2) hypertelorism with downslanting palpebral fissures
(3) lowset, posteriorly rotated ears with a thickened helix
(4) deeply grooved philtrum
(5) high, wide peaks to the vermillion border of the upper lip
(6) short neck with excess nuchal tissue
(7) low posterior hairline
(8) blue or blue-green iris
Facial features in infant:
(9) large cranium with small face
(10) thickened or ptotic lids
(11) nose with a depressed root, a wide base and bulbous tip; may appear upturned
(12) pointed chin
(13) triangular face with wide forehead and tapering sides
(14) pinched nasal root with thin bridge
(15) hair curly or wooly
Genetic testing: The precise cytogenetic abnormality has not been defined. However, genetic testing can help exclude alternative diagnoses.
Differential diagnosis – includes:
(1) Turner syndrome (in girls)
(2) trisomy 8p
(3) trisomy 22
(4) fetal alcohol syndrome
(5) intrauterine exposure to primidone
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