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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, delayed speech and language skills, distinctive facial features, sleep disturbances, and behavioral problems.
Most people 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 more distinctive in later childhood and adulthood. Dental abnormalities are also common in affected individuals.
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 affectionate, 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 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 vision problems. Although less common, heart and kidney defects also have been reported in people with Smith-Magenis syndrome.
Smith-Magenis syndrome affects at least 1 in 25,000 individuals worldwide. Researchers believe that many people with this condition are not diagnosed, however, so the true prevalence may be closer to 1 in 15,000 individuals.
Smith-Magenis syndrome is 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, in each cell 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. Although these individuals have many of the major features of the condition, they are less likely than people with a chromosomal deletion to have short stature, hearing loss, and heart or kidney abnormalities. The RAI1 gene provides instructions for making a protein whose function is unknown. Mutations in one copy of this gene lead to the production of a nonfunctional version of the RAI1 protein or reduce the amount of this protein that is produced in cells. Researchers are uncertain how changes in this protein result in the physical, mental, and behavioral problems associated with Smith-Magenis syndrome.
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. Most often, people with Smith-Magenis syndrome have no history of the condition in their family.
'''Smith-Lemli-Opitz syndrome''' is a developmental disorder that affects many parts of the body. This condition is characterized by distinctive facial features, small head size (microcephaly), mental retardation or learning disabilities, and behavioral problems. Malformations of the heart, lungs, kidneys, gastrointestinal tract, and genitalia are also common. Infants with Smith-Lemli-Opitz syndrome have weak muscle tone (hypotonia), experience feeding difficulties, and tend to grow more slowly than other infants. Most affected individuals have fused second and third toes (syndactyly), and some have extra fingers or toes (polydactyly). Smith-Lemli-Opitz syndrome affects an estimated 1 in 20,000 to 40,000 births. This condition is most common in Caucasians of European ancestry. It is very rare among African and Asian populations. This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Mutations in the ''DHCR7'' gene cause Smith-Lemli-Opitz syndrome. The ''DHCR7'' gene makes an enzyme called 7-dehydrocholesterol reductase. This enzyme is responsible for the final step in the production of cholesterol. Cholesterol is an essential nutrient that is necessary for normal embryogenesis development. Cholesterol is also a structural component of cell membranes and the protective substance covering nerve cells (myelin). Additionally, cholesterol plays an important role in the production of certain hormones and digestive acids. Mutations in the ''DHCR7'' gene reduce or eliminate the activity of 7-dehydrocholesterol reductase, preventing cells from producing enough cholesterol. A lack of this enzyme also allows potentially toxic byproducts of cholesterol production to build up in the blood and other tissues. The combination of low cholesterol levels and an accumulation of other substances likely disrupts the growth ... [ Read More ]
Syndrome X - The complete nutritional program to prevent and reverse insulin resistance. By Jack Challem, The Nutrition Reporter Burt Berkson, M.D., Ph.D. Melissa Diane Smith, nutrition counselor
New Attitudes Enhance Care of Adults with Down Syndrome - A short MCW healthlink article by Dr. David Smith regarding successful health care management of people with Down syndrome.
Smith Lemli Opitz Syndrome - Advocacy and exchange. Includes a detailed description, diagnosis, the natural history, biochemistry, genetics, treatment and contact details.
Emergency Medicine - An extensive article about Smith-Lemli-Opitz syndrome, a multiple congenital anomalies/mental retardation syndrome caused by a defect in cholesterol synthesis.
NORD: Smith Lemli Opitz Syndrome - Offers a brief description, the synonyms and further resources.
The CaF Directory - A definition of Smith-Magenis syndrome, its inheritance pattern, pre-natal diagnosis and a support group in the United Kingdom.
NORD: Smith Magenis Syndrome - Offers the synonyms, a general discussion and further resources.
PRISMS (Parents and Researchers Interested in Smith-Magenis Syndrome) - Details about the international support group organization and its mission as well as the condition. Includes an introduction, diagnosis, parent's corner, meet other people with SMS and educational considerations.
Antidote for Premenstrual Syndrome ( PMS ) - Elizabeth Smith, MD reviews the most recent research on the cause of Premenstrual Syndrome, and John Lee, MD's success in treating PMS.