QUOTE: “'Cells divide at least a billion times in the average person, usually without any problem.” Nevertheless, rare abnormalities do occur, as in the case with Down syndrome, when the wrong number of chromosomes (aneuploidy) results. ( DAVID’s bold)

DAVID: Note my bold. The level of mistakes must be very small, but like a good designer, God recognized the need for backup corrective mechanisms to cover that possibility.

dhw: There is no cure for Down’s syndrome.

And there are many others, not as well known. What we have been given has never been completely perfect.