Gatiss - who plays Mycroft in the BBC's adaptation of Sir Arthur Conan Doyle's detective stories - explained that cuts were made to 'A Study in Pink', as it was felt that the original version gave away too much about the brothers' dynamic.
Speaking during a web chat organised by Sherlock's American broadcaster PBS, Gatiss said: "[It's] far better to leave things in everyone's imaginations. It's nice to give little hints here and there but never a full answer. Why are the Holmes brothers the way they are? What are their parents like? Maybe we'll see one day.
"We actually cut a bit from 'Pink' which gave a bit too much away about the obvious frisson of animosity that exists between them. It's not there in the original stories. It comes entirely from Billy Wilder and Izzy Diamond's brilliant 'Private Life of Sherlock Holmes' and Christopher Lee's cold, disdainful Mycroft. if you haven't seen it - do!"
Gatiss added Mycroft "clearly does care about his brother", explaining: "All he wants to do is to bring him into the fold. To stop him being a loose cannon. I'd like to find a way of showing more than we have that he's actually even cleverer than Sherlock - but the deductions are hard enough as it is!"
The actor also said that he is "totally different" from his character.
"I wish I was half as clever, but I'm glad I'm not detached like him," Gatiss said. "'The Ice Man' as Moriarty calls him. He and Sherlock have both clearly decided that they mustn't get involved with human relationships. They perceive them as weaknesses."