The most common and most likely answer to this crossword clue is the 6 letter word CHOREA
I've seen this crossword clue in Financial Times
C
H
O
R
E
A
More clues leading to the result CHOREA
Buddy explains!
The straight part
We know that "Disorder" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case disorder = chorea.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CHOREA mean?
CHOREA noun- An Ancient Greek circular dance accompanied by a chorus.
- Any of the various diseases of the nervous system characterized by involuntary muscular movements of the face and extremities; St. Vitus's dance.