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Silver-Russell syndrome is characterized by growth retardation with antenatal onset, characteristic facies and limb asymmetry.
ORPHA:813Classification level: Disorder
The incidence is evaluated at 1-30/100 000 cases and about 400 cases have been reported in the literature.
Weight is often more affected than size, with little subcutaneous fat tissue. Bone maturation is delayed, in accordance with small stature. The fontanelle may be late to close. The skull has a normal circumference, which may contrast with the rest of the body and confers a pseudohydrocephalic appearance. The wide prominent forehead contrasts with the small, triangular face with a small pointed chin, a wide mouth with thin lips and down-turned corners, large eyes and bluish sclera. Lateral and usually partial asymmetry of the limbs is observed in 60% to 80% of cases, but is not progressive. Shortness and/or clinodactyly of the fifth fingers is a common finding. Patients may be slow to learn motor skills, and in rare cases, may be mildly intellectually deficient.
Etiology is heterogeneous. Most cases are sporadic. Maternal uniparental disomy of chromosome 7 is observed in 10% of patients. Approximately 30% of the cases show hypomethylation of the H19 gene, located in the 11p15 imprinted region. Hypomethylation results in most cases from an epigenetic mechanism or a genomic microrearrangement, such as a maternal microduplication of the region.
Diagnosis is mainly clinical, as there is no specific biological test, but it can be confirmed by the detection of the underlying molecular anomaly.
Differential diagnosis includes intrauterine growth retardation due to impaired placental function, structural or mosaic chromosomal abnormalities, neonatal progeria (Wiedemann-Rautenstrauch syndrome), 3M syndrome and Mulibrey dwarfism (see these terms). Genetic counselling depends on the molecular mechanism involved.
Prenatal diagnosis is not usually possible (as most cases reported so far are sporadic, the potential risk of having an affected child is not anticipated during pregnancy).
The recurrence risk is extremely low in cases of uniparental disomy of chromosome 7 or epigenetic anomalies of the 11p15 region.
Management and treatment
Treatment is supportive. Growth hormone therapy can speed up the growth and increases the final height, but does not allow the target height to be reached.
Beyond short stature and slender build, long-term prognosis is good. Hemihypotrophy is not associated with an increased tumoral risk.