Can you please define down syndrome inheritance pattern ?

There is none: You do not inherit ds from your parents in the traditional dominant or recessive fashion. During formation of the egg, only one of a pair of the 23 separate chromosomes is present so the sperm bringing 23 will reestablish the 46. Ds occurs when an extra 21 (or piece of a 21) is present in the egg after conception. This is a chromosome number change, not an inherited trait.