D's functioning was so different from the ORP the reasonable man would deem it abnormal. Case ( byrne, he was unable to control his perverted desires, successfully claimed dr as he had a AMF)
Any condition recognised by the WHO, cases Brown ( D was found guilty of manslaughter on grounds of diminishes responsibility) Ahluwalia( D was found guilty of murder but on appeal it was reduced to manslaughter on grounds of dr)
Substantially impaired 3. DR
The RMC must substantially impair D's mental responsibility to do one of three gateways