Hi Niknak
So sorry to hear about your Cocker
FN is a well-known hereditary condition but has become increasingly rare since the introduction of a control scheme by The Cocker Spaniel Club in the 1980's. More info on the condition can be found
here & as Gill says, the breeder of your dog should be informed (although you have probably done this already). Mrs Lester, Welfare Co-Ordinator of The Cocker Club, can supply you with more info on FN & would also be interested in your Cocker's pedigree. Her contact details can be found on The Cocker Club site (link given above)
HTH
Jane