Smith Magenis


What is Smith-Magenis Syndrome (SMS)?

Smith-Magenis syndrome (SMS) is a distinct and clinically recognizable genetic disorder characterized by a specific pattern of physical, behavioral, and developmental features. SMS, which was first described in the early 1980’s by Ann C.M. Smith, MA (a genetic counselor) and Ellen Magenis, MD (a cytogeneticist), is the result of a deletion of chromosome 17 (17p11.2). The chromosomal deletion occurs from a spontaneous genetic change (mutation) that happens for unknown reasons, therefore, it is not a familial disorder. SMS is considered a rare disorder and is estimated to occur in 1 out of every 25,000 live births. Currently there are over 100 cases reported, however, it is believed that SMS is widely under-diagnosed because clinical features may be subtle. It is expected that with increased awareness, the number of those identified as having SMS will increase.

Features and Characteristics

There are many characteristics associated with SMS. Not every individual has all the characteristics, however, the following is a list of traits that have been reported:

Distinct facial features: brachycephalic (short wide head), mid-face hypoplasia, prominent forehead, epicanthi folds, broad nasal bridge, pragmatism (protruding jaw), and ear anomalies
Brachydactylic (short fingers and toes)
Short stature
Hoarse, deep voice
Speech delay
Learning disability
Mental retardation (varying degrees, but have IQ’s typically in the 50-60 range)
Low muscle tone and/or feeding problems in infancy
Eye problems
Sleep disturbances
Insensitivity to pain
Behavioral problems: hyperactivity; head banging; hand/nail biting; skin picking; pulling off fingernails and/or toenails; explosive outbursts; tantrums; destructive and aggressive behavior; excitability; arm hugging/hand squeezing when excited
Engaging and endearing personalities

Less common symptoms include:

Heart defects

Scoliosis Seizures

Urinary tract abnormalities,

Abnormalities of the palate, cleft lip
Hearing impairment


The diagnosis of SMS is usually confirmed through a blood test (called a high resolution chromosome analysis), which is typically performed for the evaluation of developmental delay and/or congenital anomalies. However, in the older child, the phenotype is distinctive enough for a clinical diagnosis to be made by an experienced clinician prior to the chromosome analysis.



Mental Health / Mental Illness

Support Coordination