Smith-Magenis Syndrome

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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 cutogeneticist), 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 underdiagnosed 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: brachycephaly (short wide head), mid-face hypoplasia, prominent forehead, epicanthal folds, broad nasal bridge, prognathism (protruding jaw), and ear anomalies
• Brachydactyly (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

 

Diagnosis

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.

 

Treatment / What to Expect

There is no cure for SMS, therefore, the treatment program involves managing the child’s symptoms. The child with SMS typically displays self-injurious behavior at home and in the classroom. There are also problems with attention-seeking outbursts and aggressive behavior. For some, medication may be given to try to control some of the behaviors although, in most cases, medications aren’t particularly helpful.

In addition to behavioral problems, children with SMS tend to have speech delays. Therefore, speech therapy, starting very early on, is typically beneficial. Most will learn to communicate verbally, with sign language, and/or gestures.

Since children with SMS are often easily distracted, they tend to do better in smaller, calmer, and more focused classroom settings, where there are no more than five to seven children with one teacher and one aide. Should the class be any larger than this, the competition for the teacher’s attention increases, as does the possibility of behavioral problems. They also seem to respond positively to consistency, structure, and routines; changes in routine can provoke behavioral outbursts and tantrums. Children with SMS have difficulty in sequential processing, which makes counting, mathematical tasks, and multi-step tasks difficult. They tend to learn best with visual cues (pictures illustrating tasks, schedules, etc.). Also, since they have a fascination with electronics, the use of assistive technology may be a good tool for teaching. Children with SMS are generally very responsive to affection, praise, and other positive emotions on the part of the teacher and enjoy interaction with adults. A teacher’s positive response can often motivate a child to do well.

More than half of children with SMS have sleep disturbances, therefore, it is recommended that their room be set up so that the child is not in any danger. This may mean removing small items or other objects that can be harmful to the child and using a locking mechanism on the door so that the child cannot leave his room to wander the house.

 

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Resources

If you are interested in meeting other parents and individuals who are involved in raising a child with Smith-Magenis syndrome, the following listserv is available:

SMS List - To subscribe, click here: http://www.egroups.com/list/sms-list/info.html

For more information on Smith-Magenis syndrome, please see the following references:

• The National Human Genome Research Institute http://www.nhgri.nih.gov/DIR/MGB/SMS97/about_sms.html
• University of Kansas Medical Center http://www.kumc.edu/gec/support/smith-ma.html
• National Organization for Rare Disorders http://www.stepstn.com/cgi-win/nord.exe?proc=Redirect&type=rdb_sum&id=976.htm
• Online Mendelian Inheritance in Man http://www3.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?182290
• Baylor College of Medicine http://www.imgen.bcm.tmc.edu/molgen/lupski/sms/Index-SMS.htm