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Down-syndrome is the most common chromosomal anomaly. The human body has come together from quite a large number of cells. In each cell, there is a structure called “chromosome iplik which is a strand of genetic information. The number of chromosomes is normally 46. However, this number is 47 in Down-syndrome individuals. Down-syndrome is also called trisomy 21 because this excess chromosome is in the 21st chromosome pair.
Where does the definition of Down-Syndrome come from?
It was first described in 1866 by the British doctor J.L Down. In 1959, Frenchman J. Lejeune discovered that there are 47 chromosomes in individuals with Down syndrome. Therefore, this condition is referred to as Down syndrome in the name of the first person to describe it. Previously known as “Mongolism bu, this definition has not been used for many years.
What are Down-Syndrome types?
There are different forms of Down Syndrome. These:
Free trisomy 21:
It is the most common type. About 95% of all Down's syndrome events are of this type. Down Syndrome has all the symptoms. The number of chromosomes is 47. It is more related to the maternal age. The fact that the father's age is over fifty is also in the foreground of this type.
Translocation trisomy 21:
It usually occurs as a new phenomenon. It is found in 4-5% of cases. Although the chromosome number was found to be 46, the excess chromosome did not disappear and merged with another chromosome. There may be a 25% chromosome translocation in the family. These children have all the signs of Down's Syndrome, such as free Trisomy 21. Chromosome analysis is recommended in the family.
Mosaic trisomy 21:
It is seen in 1-2% of all Down-Syndrome cases. Some cells of the affected individuals have 46 chromosomes and some have 47 chromosomes. The findings may vary depending on the effect of cells.