ddhealthinfo.org

SMITH-MAGENIS SYNDROME

Background
Medical Management Considerations
References
Resources for Families
Advisory Committee
Publication Information

Learning Points

  • Confirm that Smith-Magenis Syndrome (SMS) is under diagnosed and sometimes confused with Down Syndrome.
  • Recognize that SMS is a distinct and clinically recognizable contiguous gene syndrome characterized by a specific pattern of physical, behavioral, and developmental features.
  • Restate the estimated occurrence of SMS (1:25,000 births) and acknowledge that it occurs equally in males and females and usually does not run in families.
  • Recognize that diagnosis of SMS is usually confirmed through karyotyping and fluorescence in situ hybridization (FISH) for the interstitial 17p11.2 deletion during the evaluation of developmental delay and/or congenital anomalies.
  • List six characteristic features of SMS; e.g.,
    • Midface hypoplasia (broad, flat midface)
    • Ocular abnormalities (85%)
    • Brachycephaly, square and broad facie (81%)
    • Prognathism
    • Down-turned mouth
    • Low pitched and hoarse voice (82%)
    • Prominent cherubic and often rosy cheeks
  • Acknowledge that heart defects, including tetralogy of Fallot, are commonly associated with SMS.
  • Delineate four referral considerations for SMS; e.g., referral
    • to behavior specialists as needed
    • for speech therapy and special education as appropriate
    • for family therapy as necessary
    • for self destructive/self injurious behavior to pediatric psychiatrist/psychologist and/or occupational therapist
  • Refer families to appropriate resources on SMS.

BACKGROUND
back to top

Description and Causes

Smith-Magenis syndrome is a distinct and clinically recognizable contiguous gene syndrome characterized by a specific pattern of physical, behavioral, and developmental features. Smith-Magenis syndrome (SMS) is caused by a de novo genetic change early in embryonic development resulting in the interstitial deletion of the chromosome 17p11.2 region. The severity of the syndrome depends upon the amount of missing genetic material.

Affected individuals may have a variety of associated symptoms and physical abnormalities, including cranio-facial dysmorphias, brachycephalia, skeletal, ocular, cardiac, genitourinary and otolaryngological anomalies such as hearing loss and an unusually deep, hoarse voice. The central nervous system is affected, with observed psychomotor retardation and intellectual deficit. Behavioral troubles are frequent, including self-injurious behavior. Some people with SMS may never show significant behavior problems, although some degree of self-injury and sleep disturbance occurs in most. Self-injurious behavior is correlated with increasing age and a lower level of intellectual functioning.

Despite their very difficult behaviors, children and adults with SMS are very appealing and affectionate. Infants have a cherubic appearance and happy disposition. IQ is generally between 20 and 70, with most affected individuals falling in the moderate range of mental retardation (40 – 54).

The search for information on SMS is formidable since public and professional awareness about SMS and its implications is not widespread. No medical prevention or cure exists at this time.

Diagnosis

Diagnosis can be made in the pre-natal period. Diagnosis is usually confirmed through karyotyping and fluorescence in situ hybridization for the interstitial 17p11.2 deletion during the evaluation of developmental delay and/or congenital anomalies. SMS is underdiagnosed. With improved molecular cytogenetic techniques and increased professional awareness of SMS, the number of SMS diagnoses grows every year. SMS babies often are thought to have Down Syndrome.

Occurrence

  • Exact incidence is not known; estimates are 1:25,000 births
  • Males and females are affected in equal numbers
  • SMS usually does not run in families

Characteristic Features

  • Midface hypoplasia (broad, flat midface)
  • Ocular abnormalities (85%)
  • Brachycephaly, square and broad facie (81%)
  • Prognathism
  • Down-turned mouth
  • Low pitched and hoarse voice (82%)
  • Prominent cherubic and often rosy cheeks
  • Unusually formed ears
  • Eye problems, including strabismus and myopia
  • Short fingers and toes
  • Hypothonia (100%)
  • Hyporeflexia (84%)
  • Scoliosis (65%)
  • Short stature
  • Developmental delay
  • Mental retardation
  • Low muscle tone
  • An unusual gait, which may be associated with a peripheral neuropathy (75%)
  • Feeding problems in infancy
  • Hoarse voice
  • Chronic ear infections/ Hearing impairment
  • Decreased sensitivity to pain
  • Sleep problems, including frequent awakenings
  • Behavioral problems such as hyperactivity, head banging, hand/nail biting, skin picking, pulling off finger and/or toenails, explosive outbursts, tantrums, destructive and aggressive behavior, excitability, arm hugging/hand squeezing when excited (75%)
  • Clinical seizures (11-30%)
  • Renal anomalies (35%)

Common Associations

  • Heart defects including tetralogy of Fallot
  • Renal/urinary tract abnormalities
  • Abnormalities of the palate

MEDICAL MANAGEMENT CONSIDERATIONS
back to top

Note: These considerations are in addition to the normal medical care provided to an individual without Smith-Magenis syndrome. All recommendations can be addressed through clinical examination by the primary care provider, unless otherwise noted.

Ongoing

  • Consider medication to alleviate hyperactivity and sleep difficulties; refer to behavior specialists as needed
  • Refer as appropriate for speech therapy and special education
  • Consider referral for family therapy as necessary
  • Consider referral for self destructive/self injurious behavior to pediatric psychiatrist/psychologist and/or occupational therapist
  • Monitor otolaryngologic and ophthalmologic health
  • Monitor dental health
  • Observe urinary tract infection for increase in renal anomalies

Infancy or Early Childhood (Birth to 5 years)

  • Refer parents for genetic counseling
  • Refer for ophthalmic assessment
  • Refer to an audiologist or otolaryngologist for assessment and intervention
  • Refer to pediatric cardiologist if necessary
  • Encourage parents to pursue speech therapy and help for hearing impaired
  • Observe for feeding problems
  • Monitor child’s learning and behavioral progress; refer to specialists as necessary
  • Observe for sleep disturbances

Late Childhood (5 to 13 years)

  • Discuss special education with parents to maximize child’s potential
  • Recheck for myopia and hearing impairments
  • Observe signs for peripheral neuropathy
  • Observe for behavioral concerns, especially components of self-injurious behavior; refer to specialists as necessary

Adolescence and Adulthood (13 years and over)

  • Monitor child’s learning and behavioral progress; refer to specialists as necessary
  • Observe for peripheral neuropathy

REFERENCES
back to top

Peer-reviewed Journal Articles/Academies

Allanson, J.E., Greenberg, F., Smith, A.C. (1999). The Face of Smith-Magenis Syndrome: A Subjective and Objective Study. Journal of Medical Genetics, 36(5), 394-397.

Dykens, E.M., Smith, A.C. (1998). Distinctiveness and Correlates of Maladaptive Behaviour in Children and Adolescents with Smith-Magenis Syndrome. Journal of Intellectual Disability Research, 42(6), 481-489.

Finucane, B.M., Haines-Dirrigl, K., Simon, E. (2001). Characterization of Self-injurious Behaviors in Children and Adults with Smith-Magenis Syndrome. American Journal on Mental Retardation, 106(1), 52-59.

Finucane, B.M. et al. (1993). Eye Abnormalities in the Smith-Magenis Contiguous Gene Deletion Syndrome. American Journal of Medical Genetics, 45(4), 443-446.

Finucane, B.M. et al. (1994). The Spasmodic Upper-body Squeeze: A Characteristic Behavior in Smith-Magenis Syndrome. Developmental Medicine and Child Neurology, 36(1), 78-83.

Greenberg, F. et al. (1991). Molecular Analysis of the Smith-Magenis Syndrome: A Possible Contiguous-gene Syndrome Associated with Del(17), (p.11.2). American Journal of Human Genetics, 49(6), 1207-1218.

Greenberg, F. et al. (1996). Multi-disciplinary Clinical Study of Smith-Magenis Syndrome (deletion 17p11.2). American Journal of Medical Genetics, 62(3), 247-254.

Hodapp, R.M., Fidler, D.J., Smith, A.C. (1998). Stress and Coping in Families of Children with Smith-Magenis Syndrome. Journal of Intellectual Disability Research, 42(5),331-340.

Smith, A. C., Dykens, E., Greenberg, F. (1998). Behavioral phenotype of Smith-Magenis Syndrome (del17 p11.2). American Journal of Medical Genetics, 81(2), 179-185.

Smith, A.C., Dykens, E., Greenberg, F. (1998). Sleep Disturbance in Smith-Magenis Syndrome (del17 p11.2). American Journal of Medical Genetics, 81(2), 186-191.

Smith, A.C., Gropman, A. (2001). Smith-Magenis Syndrome. In S.B. Cassidy, J.E. Allanson (Eds.) Management of Genetic Syndromes (pp. 363-385). New York: Wiley-Liss.

Sweeney, E. et al. (1999). Smith Magenis Syndrome and Tetralogy of Fallot. American Journal of Medical Genetics, 36(6), 501-502.

Thoene, J.G., (ed.) (1995). Physicians’ Guide to Rare Diseases, 2nd Ed. Montvale, NJ: Dowden.

Special Interest Groups/Other Publications

Genetic Alliance
4301 Connecticut Avenue NW, #404
Washington, DC 20008-2304
(800) 336-GENE helpline
(202) 966-5557
(202) 966-8553 fax
E-mail: [email protected]

National Organization for Rare Disorders, Inc. (NORD)
PO Box 8923
New Fairfield, CT 06812-8923
(203) 746-6518
E-mail: [email protected]

RESOURCES FOR FAMILIES
back to top

Parents & Researchers Interested in Smith-Magenis Syndrome (PRISMS)
76 South New Boston
Francestown, NH 03043
(603) 547-8384
E-mail: [email protected]

Smith-Magenis Syndrome Contact Group
52 Ladeside Close
Newton Mearns
Glasgow, Scotland G77-6TZ United Kingdom

Smith-Magenis Syndrome Mailing List

ADVISORY COMMITTEE
back to top

Theodore A. Kastner, M.D., M.S.
Robin L. Hansen, M.D.
Patrick J. Maher, M.D.
Terrance D. Wardinsky, M.D.

PUBLICATION INFORMATION
back to top

This document does not provide advice regarding medical diagnosis or treatment for any individual case, and any opinions or statements contained in this document are not intended to serve as a standard of medical care. Physicians are encouraged to view the considerations presented in this document in light of evolving scientific information. This document is not intended for use by the layperson. Reproduction of this document may be done with proper credit given to California Department of Developmental Services.