Down's syndrome
Records about the existence of Down's syndrome date back to the Saxons, fromwhom we have anecdotal reports of the disorder. The first medical report of the condition was not published, however, until 1866. In that year, the British physician, J. Langdon Down (1828-1896) wrote a paper dealing with "Ethnic classification of idiots." In this paper, Down described children with the disorder as "representative[s] of the great mongolian race: when placed side byside," he continued, "it is difficult to believe that the specimens comparedare not children of [Mongols]." Down based his comparison on the presence ofvertical folds of skin above a patient's eyelids, giving him or her an Oriental appearance. Edouard Séguin's (1812-1880) text on Idiocy and ItsTreatment by Physiological Means, published in the same year, also carried a detailed discussion of the disorder, then known as mongolism. The preferred name for the condition today is Down's syndrome.
Credit for the most complete early description of the disorder is usually given to two British physicians, John Fraser and Arthur Mitchell. Fraser and Mitchell discussed 62 cases of the condition, known to them as kalmuc idiocy, and suggested that it occurred as the result of bad health conditions during pregnancy. They found no evidence to suggest that the disorder was hereditary.
Over the next half century, however, the condition did indeed prove to be hereditary. In 1932 the Dutch physician P. J. Waardenberg suspected that it occurred as a result of a chromosomal abnormality. That hypothesis was confirmedin 1959 by the French pediatrician, Jerome Lejeune (1926-). Lejeune and his colleagues found that Down's patients have 47 chromosomes instead of the usual46. The 47th chromosome is a third copy of chromosome 21. Because of this characteristic, Down's syndrome is also known as trisomy 21. Although 95 percent of all Down's syndrome cases have trisomy 21, there are two other major types of the syndrome. Approximately four percent of Down's syndrome patients have translocation, in which the extra chromosome 21 has broken off and attached to another chromosome. In Mosaicism, which accounts for one percent of thecases, only certain cells have trisomy 21.
Scientists believe that Down's syndrome is a contiguous gene syndrome, meaning that most of the Down's syndrome phenotypic features are unlikely to develop from a single chromosomal region. Chromosome 21, itself, contains nearly 800 genes. Although scientists have yet to isolate all the chromosomes and genes involved in Down's syndrome, they are working on mapping of regions which play a role in determining specific syndrome traits. New methods for karyotyping, including one that uses spectrally classified chromosomes, are being usedfor identifying chromosomal abnormalities.
Down's syndrome results in retarded physical and mental growth and is, in fact, the most common identifiable form of mental retardation. Patients tend todevelop Alzheimer's disease-like dementia and die by the age of 35. Inrecent years, research and educational organizations have been very successful in helping the general public understand more about the nature and diversity of Down's syndrome patients and to see that many can lead long and productive lives.
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