Smith Magenis Syndrome

Smith Magenis Syndrome

National Organization for Rare Disorders, Inc.


It is possible that the main title of the report Smith Magenis Syndrome is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.


  • SMCR
  • SMS
  • chromosome 17, interstitial deletion 17p
  • Smith-Magenis chromosome region

Disorder Subdivisions

  • None

General Discussion

Smith-Magenis syndrome is characterized by particular facial features, developmental delays, mental retardation and behavioral abnormalities.

The facial features include a broad square-shaped face, an abnormally short, broad head (brachycephaly); an abnormally broad, flat midface; a broad nasal bridge; an unusually prominent jaw (prognathism); eyebrows growing across the base of the nose (synophrys); a short full tipped nose and fleshy upper lip with a tented appearance.

Developmental delays and intelligence are variable but most affected individuals have mild to moderate mental retardation. Behavioral abnormalities include sleep disturbances, repetitive movements (stereotypies) and a tendency to inflict harm on oneself.

Smith-Magenis syndrome occurs when there is a missing piece of chromosome on the short arm of chromosome 17 (17p11.2).


In infancy, Smith-Magenis syndrome is characterized by feeding difficulties, failure to thrive, poor muscle tone, excessive napping and lethargy. The distinctive facial appearance becomes more apparent with age. Other characteristics may include minor skeletal abnormalities, short stature, eye and ear abnormalities and speech delay. Extreme nearsightedness (myopia) and crossed eyes (strabismus) frequently occur in affected children. Other visual difficulties may include detachment of the retina of the eyes. The voice is often hoarse and low pitched. Cleft palate, heart and kidney abnormalities are sometimes present.

Developmental delays and intelligence are variable but most affected individuals have mild to moderate mental retardation. Behavioral abnormalities include sleep disturbances, a tendency to inflict harm on oneself and repetitive movements (stereotypies). Two stereotypic behaviors appear to be specific for Smith-Magenis syndrome:

Upper body squeezing and hand licking/page flipping. Self-destructive behaviors may include head-banging, wrist-biting, the insertion of foreign objects into the nose and ears (polyembolokoilamania), and pulling out the nails of the fingers and/or toes (onychotillomania).

Children with Smith-Magenis syndrome may experience significant sleep difficulties including falling to sleep and/or remaining asleep. Some children may have a decreased sensitivity to pain, burning sensations, loss of feeling in the legs (peripheral neuropathy), loss of muscle mass in the legs (amyotrophy), and absent or decreased reflexes. (For more information on this disorder, choose "peripheral neuropathy" as your search term in the Rare Disease Database.)


Smith-Magenis syndrome is a microdeletion syndrome that occurs when there is a missing piece of chromosome on the short arm of chromosome 17 (17p11.2). The vast majority of individuals with Smith-Magenis syndrome have a deletion that is the result of a new spontaneous genetic change and not from an inherited abnormality. Mutations in the RAI 1 casue SMS.

Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated "p" and a long arm designated "q". Chromosomes are further sub-divided into many bands that are numbered. For example, "chromosome 17p11.1" refers to band 11.2 on the short arm of chromosome 17. The numbered bands specify the location of the thousands of genes that are present on each chromosome.

Affected Populations

Smith-Magenis syndrome is a rare chromosome disorder that affects males and females in equal numbers. The estimated prevalence is 1/25,000 births. Smith-Magenis syndrome has been identified worldwide in many ethnic groups.

Standard Therapies


Smith-Magenis syndrome is diagnosed by the detection of a deletion of the short arm of chromosome 17 at band p11.2. This deletion can be observed following a routine chromosome analysis but is sometimes overlooked. Molecular chromosome analysis using fluorescent in situ hybridization (FISH) may be necessary to reveal extremely small deletions that cannot be seen under the microscope.


Recommended therapies include speech/language, occupational, physical and behavioral. Psychotropic medications may be useful in increasing attention and decreasing hyperactivity. Melatonin therapy may be helpful for the sleep disorder. Early intervention, special education programs and vocational training are recommended to maximize the potential of those with Smith-Magenis syndrome.

Investigational Therapies

Information on current clinical trials is posted on the Internet at All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.

For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222

TTY: (866) 411-1010


For information about clinical trials sponsored by private sources, contact:



Smith ACM, Gropman A. Smith-Magenis syndrome. In: Allanson J. Cassidy S., eds. Clinical management of common genetic syndromes. New York: Wiley-Liss, 2000.

Smith ACM, Finucane B, Smith-Magenis Syndrome. In: The NORD Guide to Rare Disorders, Philadelphia: Lippincott, Williams and Wilkins, 2003:254.


Chen KS, Potocki, L, Lupski JR. The Smith-Magenis syndrome [del (17)p11.2]: clinical review and molecular advances. Ment Retard Dev Disabil Rev 1996;2:122-129.

Greenberg R, Lewis RA, Potocki L, et al. Multi-disciplinary clinical study of Smith-Magenis syndrome (deletion 17p11.2). Am J Med Genet 1996:62:247-254.

Potocki L, Glaze D, Tan DX, et al. Circadian rhythm abnormalities of melatonin in Smith-Magenis syndrome. J Med Genet 2000;37:428-433.

Smith ACM, Dykens E, Greenberg F. The behavioral phenotype of Smith-Magenis syndrome (del17p11.2). Am J Med Genet 1998;81:179-185.

Smith ACM Dykens E. Greenberg F. Sleep disturbance in Smith-Magenis syndrome (del17p11.2). Am J Med Genet 1998;81:186-191.


Smith ACM, Allanson J, Allen AJ, et al. (Updated 3/15/04). Smith-Magenis Syndrome. In: GeneReviews at Genetests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997-2005. Available at Accessed 4/05.


Chromosome Disorder Outreach, Inc.

P.O. Box 724

Boca Raton, FL 33429-0724


Tel: (561)395-4252

Fax: (561)395-4252



PRISMS (Parents & Researchers Interested in Smith-Magenis Syndrome)

21800 Town Center Plaza

Suite 266A-633

Sterling, VA 20164


Tel: (972)231-0035

Fax: (972)499-1832



American Society for Deaf Children

800 Florida Avenue NE


Washington, DC 20002-3695

Tel: (866)895-4206

Fax: (410)795-0965

Tel: (800)942-2732



Smith-Magenis Syndrome Foundation

London, WC1 N3XX

United Kingdom

Tel: 02074195007



Genetic and Rare Diseases (GARD) Information Center

PO Box 8126

Gaithersburg, MD 20898-8126

Tel: (301)251-4925

Fax: (301)251-4911

Tel: (888)205-2311

TDD: (888)205-3223


Madisons Foundation

PO Box 241956

Los Angeles, CA 90024

Tel: (310)264-0826

Fax: (310)264-4766



Taylor Bug Kisses Foundation

2218 Boulder Dr.

Normal, IL 61761

Tel: (309)451-1431



For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders, Inc.® (NORD). Cigna members can access the complete report by logging into For non-Cigna members, a copy of the complete report can be obtained for a small fee by visiting the NORD website. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational treatments (if available), and references from medical literature. For a full-text version of this topic, see

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use . How this information was developed to help you make better health decisions.

Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.