Silly Book, Silly Premise, but a little late for the Church to say anything about it. Most people know it is fantasy because they are like children who only soak in what they are prepared to know. Most people hardly know L DaVinci, art, theology, etc... The more you know the more you think people pick up. Most people I talked to who read the book have forgotten about it. I think it is a mistake to make a big deal over it.
Beyond the Jesus bloodline hokum, the accusation of the book is that the Catholic hierarchy used Christianity to suit their own political ends. Any Protestant has to agree with at certain percentage of that statement.