What’s regularly encountered in adults is some tendency to detachment (6)
I believe the answer is:
autism
'tendency to detachment' is the definition.
I can't judge whether this definition defines the answer.
'what's regularly encountered in adults is some' is the wordplay.
'what's regularly encountered in' means one should take alternating letters (letters taken at regular intervals).
'adults'+'is'+'some'='adultsissome'
The alternating letters of 'adultsissome' are 'AUTISM'.
Can you help me to learn more?
(Other definitions for autism that I've seen before include "Mental condition where sufferer withdraws into private world of fantasy" , "Condition characterized by difficulty in communicating and forming relationships" , "Mental illness that isolates from the real world" , "Condition with great difficulty in communicating" , "Form of mental illness causing one to withdraw into private world" .)