if ur using a custom tx and rx u can send even 16 bit using protocol similar to uart. but not in standard pc uart implementation because the 16550 uart chip in mother biard has 8 bit wide buffer only.
if u hav send 16 bit data to pc by splitting it, this can be combined to 16 bit back easily by writing a small piece of code, in c , c++ (examples available jus google it) to acewes the uart register and combine the words
reagarding matlab i'm not 100% sure but they should hav provided some ways to capture the data from uart.