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1、DownDown syndromesyndrome, or DownsDowns syndromesyndrome (primarily in the United Kingdom),12 trisomytrisomy 2121, or trisomytrisomy G G, is a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British physician who descr
2、ibed the syndrome in 1866. The disorder was identified as a chromosome 21 trisomy by Jrme Lejeune in 1959. The condition is characterized by a combination of major and minor differences in structure. Often Down syndrome is associated with some impairment of cognitive ability and physical growth, and
3、 a particular set of facial characteristics. Down syndrome in a fetus can be identified with amniocentesis during pregnancy, or in a baby at birth.Individuals with Down syndrome tend to have a lower than average cognitive ability, often ranging from mild to moderate developmental disabilities. A sma
4、ll number have severe to profound mental disability. The incidence of Down syndrome is estimated at 1 per 800 to 1,000 births, although it is statistically much more common with older mothers. Other factors may also play a role.Many of the common physical features of Down syndrome may also appear in
5、 people with a standard set of chromosomes, including microgenia (an abnormally small chin)3, an unusually round face, macroglossia4 (protruding or oversized tongue), an almond shape to the eyes caused by an epicanthic fold of the eyelid, upslanting palpebral fissures (the separation between the upp
6、er and lower eyelids), shorter limbs, a single transverse palmar crease (a single instead of a double crease across one or both palms, also called the Simian crease), poor muscle tone, and a larger than normal space between the big and second toes. Health concerns for individuals with Down syndrome
7、include a higher risk for congenital heart defects, gastroesophageal reflux disease, recurrent ear infections, obstructive sleep apnea, and thyroid dysfunctions.Early childhood intervention, screening for common problems, medical treatment where indicated, a conducive family environment, and vocatio
8、nal training can improve the overall development of children with Down syndrome. Although some of the physical genetic limitations of Down syndrome cannot be overcome, education and proper care will improve quality of life.5CharacteristicsCharacteristicsIndividuals with Down syndrome may have some o
9、r all of the following physical characteristics: microgenia (abnormally small chin)3, oblique eye fissures with epicanthic skin folds on the inner corner of the eyes (formerly known as a mongoloid fold4), muscle hypotonia (poor muscle tone), a flat nasal bridge, a single palmar fold, a protruding to
10、ngue (due to small oral cavity, and an enlarged tongue near the tonsils) or macroglossia4, a short neck, white spots on the iris known as Brushfield spots,6 excessive joint laxity including atlanto-axial instability, congenital heart defects, excessive space between large toe and second toe, a singl
11、e flexion furrow of the fifth finger, and a higher number of ulnar loop dermatoglyphs. Most individuals with Down syndrome have mental retardation in the mild (IQ 5070) to moderate (IQ 3550) range,7 with individuals having Mosaic Down syndrome typically 1030 points higher.8 In addition, individuals
12、with Down syndrome can have serious abnormalities affecting any body system. They also may have a broad head and a very round face.The medical consequences of the extra genetic material in Down syndrome are highly variable and may affect the function of any organ system or bodily process. The health
13、 aspects of Down syndrome encompass anticipating and preventing effects of the condition, recognizing complications of the disorder, managing individual symptoms, and assisting the individual and his/her family in coping and thriving with any related disability or illnesses.7Down syndrome can result
14、 from several different genetic mechanisms. This results in a wide variability in individual symptoms due to complex gene and environment interactions. Prior to birth, it is not possible to predict the symptoms that an individual with Down syndrome will develop. Some problems are present at birth, s
15、uch as certain heart malformations. Others become apparent over time, such as epilepsy.The most common manifestations of Down syndrome are the characteristic facial features, cognitive impairment, congenital heart disease (typically a ventricular septal defect), hearing deficits (maybe due to sensor
16、y-neural factors, or chronic serous otitis media, also known as Glue-ear), short stature, thyroid disorders, and Alzheimers disease. Other less common serious illnesses include leukemia, immune deficiencies, and epilepsy.However, health benefits of Down syndrome include greatly reduced incidence of many common malignancies except leukemia and testicular cancer9 although it is, as yet, unclear whethe
