After the diagnosis has been submitted to The American Psychiatric Association next convention,  The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) their classification and diagnostic tool, will be updated after their vote to reflect that definition.

That's how "gender identity disorder"  became "gender dysphoria" in the 2013 version.  And how 'Asperger syndrome' lost its separate classification.

"Mental illness" is what they vote to say it  is, after all.  

That's what passes for 'science' in the psychiatric field; majority votes of those present.