The deleted segment most often includes approximately 3.7 million DNA building blocks (base pairs), also written as 3.7 megabases (Mb). This deletion occurs on the short (p) arm of the chromosome at a position designated p11.2. In most people with Smith-Magenis syndrome, the condition results from the deletion of a small piece of chromosome 17 in each cell. Although less common, heart and kidney defects also have been reported in people with Smith-Magenis syndrome. Affected individuals may have eye abnormalities that cause nearsightedness ( myopia ) and other vision problems. Some people with this disorder have ear abnormalities that lead to hearing loss. Other signs and symptoms of Smith-Magenis syndrome include short stature, abnormal curvature of the spine ( scoliosis ), obesity, and a hoarse voice. People with Smith-Magenis syndrome may have other behaviors, such as repetitive self-hugging or compulsively licking their fingers and flipping pages of books and magazines (a behavior known as "lick and flip"). Self-injury, including biting, hitting, head banging, and skin picking, is very common. These include frequent temper tantrums and outbursts, aggression, anxiety, impulsiveness, and difficulty paying attention. People with Smith-Magenis syndrome typically have affectionate, engaging personalities, but most also have behavioral problems. Affected people may have trouble falling asleep at night and awaken several times during the night and early morning. Dental abnormalities are also common in affected individuals.ĭisrupted sleep patterns are characteristic of Smith-Magenis syndrome, and they typically begin early in life. These facial differences can be subtle in early childhood, but they usually become more distinctive in later childhood and adulthood. The mouth tends to turn downward with a full, outward-curving upper lip. The middle of the face and the bridge of the nose often appear flattened. Most people with Smith-Magenis syndrome have a broad, square-shaped face with deep-set eyes, full cheeks, and a prominent lower jaw. The major features of this condition include distinctive facial features, sleep disturbances, behavioral problems, mild to moderate intellectual disability, and delayed speech and language skills. Smith-Magenis syndrome is a developmental disorder that affects behavior, emotions, and learning processes.
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