Biology Honors.
10 Jan. 2011
Chromosome Abnormality
Chromosome Abnormality happens at conception when the sperm and the egg meet. A whole chromosome might be missing, or part of a chromosome might have been deleted or replicated. The risk of the abnormal conception depends on the parents’ ages. The risk is higher with older parents, and it is not sex-linked.The abnormal chromosome count can cause many syndromes, including the Smith-Magenis Syndrome.
Smith-Magenis Syndrome is a relatively rare chromosomal abnormality caused by a deletion of few genes in chromosome 17. In most cases, “the deletion occurs accidentally at conception when an abnormal sperm or egg from one parent unites with a normal sperm or egg from the other parent” where the abnormal sperm or egg contains the missing chromosomal material (Stolmski). Even though it is related to genetic material, Smith-Magenis Syndrome does not run in families. It is diagnosed in “at least 1 in 25,000 individuals worldwide,” but scientists believe that many people are not even diagnosed with the syndrome, so “at least 1 in 25,000 individuals worldwide” may be affected (NIH).
People affected with the syndrome usually have characteristic facial features of “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” (NIH). Less common “feature includes cleft lip” (Slomski). At first, the characteristics suggest that these people have Down syndrome. The features are subtle during childhood, especially early on, but they became more distinctive as the patient grows older.
Even though the facial features suggest the diagnosis, the behavior suggests the diagnosis earlier. Beginning early in life, disrupted sleep patterns are common. “Affected people may be very sleepy during the day, but have trouble falling asleep and awaken several times each night” (NIH). People with the syndrome may have affectionate personalities, but also has behavioral problems such as “hyperactivity, head banging, hand/nail biting, skin picking, pulling off fingernails and toenails, explosive outbursts, tantrums, destructive and aggressive behavior, excitability, arm hugging/squeezing when excited” (Slomski). Some other symptoms for the syndrome include “short stature, deep and hoarse voice, speech delay, learning disabilities, ear infections, poor muscle tone, and mental retardation with range of 50-60 for IQ” (Stolmski). Eye disorders are also common along with insensivity to pain. Scoliosis may occur, and “ear infections, if chronical enough, may lead to complete deafness” (Stolmski).
Study of eleven children with Smith-Magenis Syndrome less than three years of age shows that “Infants aged approximately 1 year or younger exhibited cognitive, language, and motor skills that ranged from average to delayed, but with age-appropriate social skills and minimal maladaptive behaviors. At