Down's syndrome is caused by trisomy of chromosome 21. Trisomy refers to the presence of three copies of one chromosome in the genome. Since David has extra genetic material in chromosome 21, he is suffering from Down's syndrome.
Down's syndrome would affect the mental development and learning process of David. He is likely to have a broad skull with a small mouth.
The best material for this purpose is vulcanized rubber. Jogging strollers have wider bases and larger wheels to stabilize them, and these wheels must be durable in order to withstand the stresses introduced during the high speed movement.
