Down syndrome is cause by a baby chromosomes. the baby has an extra chromosome.
Most people with down syndrome have distinctive facial features, short neck, legs, and arms, and could have been born with heart, intestine, ear and breathing problems.
There is no single treatment , but they are based on each of the persons problem.
Life Expectancy from 50 to 60 years in the 2000's.
1) happens with one extra chromosome
2) 3 types of down syndrome.( Trimosy 21, translocation, and mosasiasm.