It's possible to get Down Syndrome from a duplication of one of the 21st chromosomes. Down Syndrome=Trisomy 21.
Down's Syndrome Kleinfelter's Syndrome
The disease sickle cell anaemia occurs due to a mutation. This causes the amino acid glutamic acid (which is hydrophilic) in haemoglobin to be replaced by valine (which is hydrophobic).
its a change in your DNA
cancer or a tumor