Down Syndrome is the first and best recognized as well as the most frequent human chromosomal syndrome. Down syndrome or trisomy 21 is a disorder in the genes due to the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British doctor who first described it in 1866. The manifestations consist mainly of physical abnormalities and mental retardation as a result of developmental defects.
Generally, it can be said that anomalies ranging from slight to severe have been found in almost all tissues of the body but the name of the syndrome is derived from the obliquely set, slanting eyes that can be shown most of the patients. The incidence of Down syndrome is estimated at 1 per 800 to 1 per 1,000 births (Buckley, 2000). Furthermore according to Buckley, S. (2000) the incidence in the general population is 1 in 600 to 800 live births. However, among all conceptuses, it is possible that more than twice this frequency occurs since greater than half of the trisomy 21 fetuses are spontaneously aborted during early pregnancy.
Del Mundo, et al, (1982) mentioned that the outward characteristics of the condition are well known. Down Syndrome is showed by the trisomy of a chromosome belonging to the G group, specifically chromosome No. 21. It has 47 as its total chromosome number. It can be noted that a high correlation exists between increasing maternal age and the non disjunction resulting in the extra chromosome of offspring, though the reason of this is still unknown.
The additional number is presumed to be the result of nondisjunction during the meiotic process in the parental, usually the maternal, gamete, since the condition has been seen to be more frequent among infants of aging mothers. A second type of aberration occasionally seen in cases of Down syndrome as mentioned in the online encyclopedia of Wikipedia (2006) it is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on the 21st chromosome, either in whole (trisomy 21) or part as caused by translocation between a No.
21 chromosome and a chromosome in the 13 and 15 group which for shortness is called D/G translocation. This is seen in families where several numbers are affected with Down Syndrome (familial Down Syndrome), and in cases born of unusually young mothers. These children have 46 chromosomes and the translocstion is apparently transmitted by clinically normal women with 45 chromosomes. A third chromosomal deviation is a translocation involving the G group, either a 21/21 translocation or a 21/22 translocation (G/G translocation). Carriers are male, especially the elderly males.
With Strom (2006) Mosaicism has been reported in 2 to 3 percent of patients with Down Syndrome which is 10-30 points higher than those with the mild to moderate who are having mental retardation. It is advisable to determine the karyotype of the child with Down syndrome since recurrence risks are higher in translocation cases than in those with trisomy. No gross changes in the central nervous system are presented to children with Down Syndrome. Their mental abilities as observed are often in the trainable and slightly educable ranges.
In fact Homeier (2005) showed that these days, many children with Down syndrome grow up going to school and enjoying many of the same activities as other kids their age, and they were found to be active, happy and enjoy music a lot. And as they grow up they undergo many transition to semi-independent living. Somehow in all these problems in Down Syndrome cases a pregnant women can already be screened for various complications in their pregnancy to avoide or lessened occurences. Standard prenatal screens can already reveal possibilities of occurences of Down syndrome.
There is now an offer of genetic counseling along with genetic testing, such as amniocentesis, chorionic villus sampling (CVS), or percutaneous umbilical blood sampling (PUBS) to families who may have the possibility of having a child with Down syndrome, or where normal prenatal exams would show possible problems. Screening of genes are often performed on pregnant women older than 30 or 35 (Down Syndrome Research Foundation, 2005). Reference Barbara P. Homeier, B. P. (2005). Down Syndrome. Available: http://www. kidshealth.
org/parent/medical/genetic/down_syndrome. html. Buckley, S. (2000). Living with Down Syndrome. Portsmouth, UK: The Down Syndrome Educational Trust. Down Syndrome Research Foundation (2005). Bright Beginnings: A Guide for New Parents. Buckinghamshire, UK: Down Syndrome Research Foundation. Strom, C. (1999). Wha tis down syndrom FAQ. Retrieved on 2006-06-03 from Mosaic Down Syndrome Society. Available: http://www. mosaicdownsyndrome. com/faqs. htm. Wikipedia. (2006). Down Syndrome. Available: http://en. wikipedia. org/wiki/Down_syndrome.