There are three major types of Down Syndrome.
Trisomy 21 is the presence of extra genetic material on the 21st pair of chromosomes resulting from an anomaly in cell division during development of the egg or sperm or during fertilization. About 95% have Trisomy 21.
Translocation is where the extra chromosome 21 broke off and became attached to another chromosome. About 4% have Translocation.
Mosaicism is where only some cells have Trisomy 21. About 1% have Mosaicism. Some of the characteristics of Down Syndrome are almond shaped eyes, small ears, small head size, short, broad hands with a single transverse palmar crease. Mental disabilities of varying degrees is also common . Down Syndrome affects approximately 250,000 people in the United States.