PTPN11

LEOPARD Syndrome

Clinical Characteristics
Ocular Features: 

Ocular hypertelorism is a characteristic of all forms of the LEOPARD syndrome.  The lid fissures may be downward slanting.  Combined with the inverted triangle facies, the appearance is similar to that of the Noonan syndrome (163950).

Systemic Features: 

This is a multisystem disorder manifest in skin, heart, skeletal, genital, neurologic and auditory systems.  Generalized lentiginosis is characteristic but they may not be present until age 4 or 5 years following the appearance of cafe-au-lait spots.  Some patients have patchy scalp hair loss.  The facies bears some resemblance to the Noonan syndrome but usually without the short, webbed neck.  Sensorineural hearing loss is found in 20% of individuals.  Cardiac conduction defects, pulmonic stenosis, and hypertrophic cardiomyopathy are often (85%) present.  Cognitive defects are present in 30% of patients and some individuals have been described as mentally retarded.  Juvenile behavior may be evident in the presence of normal intelligence.  Hypospadias, cryptorchidism, and gonadal infantilism have been seen in some patients.  The ears are often malformed (87%).  Thoracic skeletal anomalies have been described in 75% of patients.  Although somatic growth is described as slow, short stature is present in less than half of patients.

Rare patients without lentigines are said to resemble the Noonan syndrome (163950) in appearance.

Genetics

Heterozygous mutations in the PTPN11 gene (12q24) are most frequently responsible for this autosomal dominant disorder.  The same gene is mutated in more than half of patients with the Noonan syndrome (NS1)(163950) with which it is allelic.  Other mutations that cause what is called LEOPARD syndrome are RAF1 and BRAF.

Other types of LEOPARD syndrome such as LEOPARD syndrome 2 (611554) are far more rare but also share mutations with Noonan syndrome (RAF1 mutations in Noonan syndrome 5) (611553) and LEOPARD syndrome 3 (613707) with mutations in BRAF similar to that seen in NS7 (613706).

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Assistive hearing devices, especially cochlear implants, may be helpful.  Special education can be of value in more mildly affected individuals.Treatment of cryptorchidism is similar to that of other children.

References
Article Title: 

Noonan Syndrome

Clinical Characteristics
Ocular Features: 

Noonan syndrome has prominent anomalies of the periocular structures including downward-slanting lid fissures, hypertelorism, epicanthal folds, high upper eyelid crease, and some limitation of ocular mobility most commonly of the levator.  Ptosis and strabismus are present in nearly half of patients. Amblyopia has been found in one-third of patients and almost 10% have nystagmus.  Corneal nerves are prominent and a substantial number of individuals have optic nerve abnormalities including drusen, hypoplasia, colobomas and myelinated nerves.  Evidence of an anterior stromal dystrophy, cataracts, or panuveitis is seen in a minority of patients.  About 95% of patients have some ocular abnormalities.

Systemic Features: 

Patients are short in stature.  Birth weight and length may be normal but lymphedema is often present in newborns.  The neck is usually webbed (pterygium colli) and the ears low-set.  The sternum may be deformed.  Cardiac anomalies such as coarctation of the aorta, pulmonary valve stenosis, hypertrophic cardiomyopathy, and septal defects are present in more than half of patients.  Dysplasia of the pulmonic valve has been reported as well.  Thrombocytopenia and abnormal platelet function with abnormalities of coagulation factors are found in about 50% of cases resulting in easy bruising and prolonged bleeding.  Cryptorchidism is common in males.  Some patients have intellectual disabilities with speech and language problems.  Most have normal intelligence.   

Parents of affected children often have subtle signs of Noonan Syndrome.

Genetics

This is an autosomal dominant disorder that can result from mutations in at least 7 genes.  Nearly half are caused by mutations in the PTPN11 gene (12q24.1) (163950).  Mutations in the SOS1 gene (2p22-p21) cause NS4 (610733) and account for 10-20% of cases, those in the RAF1 gene (3p25) causing NS5 (611553) for about the same proportion, and mutations in the KRAS gene (12p12.1) (NS3; 609942) cause about 1%.  Mutations in BRAF (7q34) causing NS7 (613706), NRAS (1p13.2) responsible for NS6 (613224), and MEK1 genes have also been implicated and it is likely that more mutations will be found.  The phenotype is similar in all individuals but with some variation in the frequency and severity of specific features.  New mutations are common. 

Several families suggestive of autosomal recessive inheritance (NS2) (605275) have been reported but no homozygous genotype has been identified.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

There is no treatment for most of the developmental problems but some patients benefit from special education. Cardiac surgery may be required in some cases to correct the developmental defects.  Bleeding problems can be treated with supplementation of the defective coagulation factor.  Growth hormone therapy can increase the growth velocity.

References
Article Title: 

Update on turner and noonan syndromes

Chacko E, Graber E, Regelmann MO, Wallach E, Costin G, Rapaport R. Update on turner and noonan syndromes. Endocrinol Metab Clin North Am. 2012 Dec;41(4):713-34. Epub 2012 Sep 28.

PubMed ID: 
23099266
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