Smith-Magenis syndrome

Smith-Magenis Syndrome (SMS) is a developmental disorder that affects many parts of the body. The major features of this condition include mild to moderate mental retardation, distinctive facial features, sleep disturbances, and behavioral problems. Smith-Magenis syndrome affects an estimated 1 in 25,000 individuals.

The syndrome is due to an abnormality in the short (p) arm of chromosome 17 and is sometimes called the 17p- syndrome.

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Eponym

The eponym Smith-Magenis refers to two workers who described the condition in 1986, namely, Ann C. M. Smith, a genetic counselor at the National Institutes of Health, and R. Ellen Magenis, a pediatrician, medical geneticist and cytogeneticist at the Oregon Health Sciences University.^[1][2]

Common symptoms

Most children with Smith-Magenis syndrome have a broad, square-shaped face with deep-set eyes, full cheeks, and a prominent lower jaw. The middle of the face and the bridge of the nose often appear flattened. The mouth tends to turn downward with a full, outward-curving upper lip. These facial differences can be subtle in early childhood, but they typically become coarser and more distinctive in later childhood and adulthood.

Disrupted sleep patterns are characteristic of Smith-Magenis syndrome, typically beginning early in life. Affected people may be very sleepy during the day, but have trouble falling asleep and awaken several times each night, due to an inverted circadian rhythm of melatonin.

People with Smith-Magenis syndrome have engaging personalities, but most also have behavioral problems. These include frequent temper tantrums and outbursts, aggression, anxiety, impulsiveness, and difficulty paying attention. Self-injury, including biting, hitting, head banging, and skin picking, is very common. Repetitive self-hugging is a behavioral trait that may be unique to Smith-Magenis syndrome. People with this condition also compulsively lick their fingers and flip pages of books and magazines (a behavior known as "lick and flip").

Other symptoms the syndrome can include short stature, abnormal curvature of the spine (scoliosis), reduced sensitivity to pain and temperature, and a hoarse voice. Some people with this disorder have ear abnormalities that lead to hearing loss. Affected individuals may have eye abnormalities that cause nearsightedness (myopia), strabismus, and other problems with vision. Heart and kidney defects also have been reported in people with Smith-Magenis syndrome, though they are less common.

Genetics

Smith-Magenis syndrome is a chromosomal condition related to chromosome 17. Most people with SMS have a deletion of genetic material from a specific region of chromosome 17 (17p11.2). Although this region contains multiple genes, recently researchers discovered that the loss of one particular gene the retinoic acid induced 1 or RAI1 is responsible for most of the characteristic features of this condition^[3]. Also, other genes within the chromosome 17 contribute to the variability and severity of the clinical features. The loss of other genes in the deleted region may help explain why the features of Smith-Magenis syndrome vary among affected individuals. A small percentage of people with Smith-Magenis syndrome have a mutation in the RAI1 gene instead of a chromosomal deletion.

These deletions and mutations lead to the production of an abnormal or nonfunctional version of the RAI1 protein. The function of the RAI1 protein is unknown, and groups led by James Lupski (Baylor College of Medicine) and Sarah Elsea (Virginia Commonwealth University) are in the process of studying the exact role for this gene.

SMS is typically not inherited. This condition usually results from a genetic change that occurs during the formation of reproductive cells (eggs or sperm) or in early fetal development. People with Smith-Magenis syndrome most often have no history of the condition in their family.

Diagnosis

SMS is usually confirmed by blood tests called chromosome (cytogenetic) analysis and utilize a technique called FISH (fluorescent in situ hybridization). The characteristic micro-deletion was sometimes overlooked in a standard FISH test, leading to a number of people with the symptoms of SMS with negative results.

The recent development of the FISH for 17p11.2 deletion test has allowed more accurate detection of this deletion. However, further testing is required for variations of Smith-Magenis syndrome that are caused by a mutation of the RAI1 gene as opposed to a deletion.

Children with SMS are often given psychiatric diagnoses such as autism, attention deficit/hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), attention deficit disorder (ADD) and/or mood disorders.

Treatment

Treatment for Smith-Magenis syndrome relies on managing its symptoms. Children with SMS often require several forms of support, including physical therapy, occupational therapy and speech therapy. Support is often required throughout an affected person's lifetime.

Medication is often used to address some symptoms. Melatonin supplements and trazodone are commonly used to regulate sleep disturbances. Other medications (such as risperdal) are sometimes used to regulate violent behavior.

See also

• Serine hydroxymethyltransferase

References

1. ^ synd/3884 at Who Named It
2. ^ Smith AC, McGavran L, Robinson J, et al (1986). "Interstitial deletion of (17)(p11.2p11.2) in nine patients". Am. J. Med. Genet. 24 (3): 393-414. doi:10.1002/ajmg.1320240303. PMID 2425619.
3. ^ Girirajan S, Vlangos CN, Szomju BB, Edelman E, Trevors CD, Dupuis L, Nezarati M, Bunyan DJ, Elsea SHGenotype-phenotype correlation in Smith-Magenis syndrome: evidence that multiple genes in 17p11.2 contribute to the clinical spectrum.Genet Med. 2006 Jul;8(7):417-27,pmid:16845274.

This article incorporates public domain text from The U.S. National Library of Medicine