The number’s upside down in this issue (3)
I believe the answer is:
son
'this issue' is the definition.
(issue can mean someone's offspring)
'the number's upside down' is the wordplay.
'the number's' becomes 'nos' (no. is a kind of number).
'upside down' says the letters should be written in reverse.
'nos' written backwards gives 'SON'.
'in' is the link.
(Other definitions for son that I've seen before include "Male child" , "Male scion" , "Male descendant" , "Heir" , "A relative" .)