(MIM 182 290)

(microdeletion 17p11.2)

Rare: incidence estimated at 1/25.000. Association of malformations caused in 90% of cases by a de novo microdeletion on the 17p11.2 region; in other cases, there is a mutation of the RAI1 gene located in the same area of this chromosome (less severe phenotype ?).

Clinical features:

-         facial dysmorphism: brachycephaly with flat face (malar hypoplasia), bulging forehead, poorly fringed ears, upslanting palpebral fissures, synophrys, 

-         micrognathia in childhood but prognathism with square adolescent face

-         hoarse voice, sometimes nodules on vocal cords

-         brachydactyly and syndactyly of toes 2-3; persistence of fetal pads on the finger pulp

-         dental abnormalities: agenesis of premolars, taurodontia; arched palate, palatopharyngeal dysfunction

-         short stature with short extremities;  android type obesity in adolescence 

-         slight motor retardation with hypotonia in infancy

-         mental retardation (IQ 20-78) with speech delay

-         sleep and behavior disorders (from the age of 2-3 years: violent anger) probably due to an inversion of the cycle of   melatonin secretion. stereotyped movementsf

-         self-harm: biting of the hands, introduction of foreign objects into body orifices; increased threshold for pain or insensitivity to pain ?

-         epilepsy in 10-30 %; MRI: cyst of the posterior fossa

-         congenital heart disease (30%): ASD, VSD, valvular stenosis, tetralogy of Fallot

-         renal abnormalities: agenesis, hydronephrosis, megaureter

-         ENT: sensorineural hearing impairment in 35 % of cases, recurrent ear infections, cholesteatoma)

-         sometimes: laryngeal anomalies, cleft lip palate, eye anomalies (coloboma), scoliosis, hypothyroidism.

in case of very large deletion: signs of hereditary neuropathy, sensitive to the pressure (see this term).

Treatment: melatonin in the evening and β-blockers in the morning, speech and behavioural support.

Anesthetic implications: 

mental retardation, and disorders of the behavior with aggressiveness; echocardiography; thyroid function; treatment by β-blocker.

References :  

-          Livet MO, Moncla A, Delobel B, Croquette MF, Philip N, Vallée L. 
Le syndrome de Smith-Magenis. 
Arch Pédiatr 1997 ; 4 : 1231-7.

-        Poisson A, Nicolas A, Sanlaville D, Cochat P, De Leersnyder H et al. 
Le syndrome de Smith-Magenis, une association unique de troubles du comportement et du cycle veille/sommeil. 
Arch Fr Pédiatr 2015 ; 22 : 638-45.

Updated: September 2018