Smith-Magenis Syndrome

What is Smith-Magenis syndrome?

Smith-Magenis syndrome 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 behavioural problems.

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 usually 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.

People with Smith-Magenis syndrome have endearing, engaging personalities, but most also have behavioural 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 behavioural 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 behaviour known as "lick and flip").

Other signs and symptoms of Smith-Magenis syndrome 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) and other problems with vision. Heart and kidney defects also have been reported in people with Smith-Magenis syndrome, though they are less common.

How common is Smith-Magenis syndrome?

Smith-Magenis syndrome affects at least 1 in 25,000 individuals and has been reported in more than 100 people worldwide.

What are the genetic changes related to Smith-Magenis syndrome?

Smith-Magenis syndrome is a chromosomal condition related to chromosome 17.

Mutations in the RAI1 gene cause Smith-Magenis syndrome.

Most people with Smith-Magenis syndrome have a deletion of genetic material from a specific region of chromosome 17. Although this region contains multiple genes, researchers believe that the loss of one particular gene, RAI1, is responsible for most of the characteristic features of this condition. 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 mutations lead to the production of an abnormal or nonfunctional version of the RAI1 protein. The function of the RAI1 protein is unknown, and researchers are uncertain how a loss of this protein results in the physical, mental, and behavioural problems associated with Smith-Magenis syndrome.

Can Smith-Magenis syndrome be inherited?

Smith-Magenis syndrome 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.

What other names do people use for Smith-Magenis syndrome?

• chromosome 17p deletion syndrome
• deletion 17p syndrome
• SMS
• 17p- syndrome