Folie à deux
Newer studies seem to indicate that this classification may not be sufficient to fully describe 'folie à deux'. There may be more symptoms than are usually described in the cases above. Also, in many cases, separating the two patients may not be enough to make the condition go  away in one of them. Also, the person described as "sane" before developing the folie à deux may already be suffering from a psychiatric illness, or may develop one.