A group of investigators round little girl -- medical problem (8)
I believe the answer is:
acidosis
'medical problem' is the definition.
'a group of investigators round little girl' is the wordplay.
'group of investigators' becomes 'cid' (Criminal Investigation Department).
'round' becomes 'o' (round can mean a round object).
'little girl' becomes 'sis' (I've seen this in other clues).
'a'+'cid'+'o'+'sis'='ACIDOSIS'
(Other definitions for acidosis that I've seen before include "A disco is (anag) - an imbalance in the blood" , "Blood disorder involving low pH" .)