Down Syndrome (cont.)
IN THIS ARTICLE
Down Syndrome Risk Factors
Advanced maternal age is the only known risk factor for Down syndrome. The older the woman is when she delivers the infant, the higher the chances of having a child with Down syndrome.
Couples who have had one child with Down syndrome are at a slightly increased risk (about 1%) for having another affected child. The risk of having a baby with Down syndrome is increased, if one of the parents has a translocation involving chromosome 21. The recurrence risk is as high as 100% if the carrier parent has a translocation in which two chromosomes 21 are fused.
People with Down syndrome rarely reproduce. About 15% to 30% of women with trisomy 21 are fertile, and they have a 50% risk of having an affected child. Men with Down syndrome are even less fertile, but at least one case is known, in which a man with Down syndrome fathered a child.
Down Syndrome Symptoms (the Effects of Trisomy 21)
It is now well known that the extra genes on the additional chromosome 21 are the cause of Down syndrome. Scientists are trying to determine which of the genes on chromosome 21 cause different characteristics of the disorder when present in three copies. Some genes may be more active and others less active due to the extra copy, and some of the genes may have a stronger influence on the characteristics of Down syndrome than others. Currently, about 400 genes on chromosome 21 have been identified, but the function of most remains unknown.
Until recently, scientists hypothesized that the most important genes involved in Down syndrome were located in an area on chromosome 21 called the Down syndrome critical region. However, scientists have found that genes outside this region are also important in Down syndrome.
Down Syndrome Characteristic Features
Despite the variability in Down syndrome, individuals with Down syndrome have a widely recognized characteristic appearance. Typical facial features include a flattened nose, small mouth, protruding tongue, small ears, and upward slanting eyes. The inner corner of the eyes may have a rounded fold of skin (epicanthal fold). The hands are short and broad with short fingers, and may have a single palmar crease. White spots on the colored part of the eye called Brushfield spots may be present. Babies with Down syndrome often have decreased muscle tone at birth. Normal growth and development is usually delayed and often individuals with Down syndrome don't reach the average height or developmental milestones of unaffected individuals.
Medically Reviewed by a Doctor on 5/10/2016
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