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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.
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]
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 may also compulsively lick their fingers and flip pages of books and magazines (a behavior known as “lick and flip”), as well as possessing an impressive ability to recall a wide range of small details about people or subject-specific trivia.
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.
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