Question about the double merle gene?

I know it common in Australian Shepherd, Border Collies and Great Danes but what other dog breeds is it most common in? And is it really accurate to call it Lethal White in dogs because I heard that horses that are born with Lethal White Syndrome usually die or have to be euthanized because there is something wrong with their colons, where dogs are usually blind, deaf or both but they don't die from it unless the breeder euthanizes them. Am I right? Anyway, thank you for your answers.