Italian to English Bus/Financial Finance (general) Mortgage certificate

Appears on a document headed up "Attestazione degli interessi passivi e degli oneri accessori sui mutui ipotecari" as one of the references at the top right hand of the page, i.e. "mutuo padre no. XXXXXX", under "mutuo no. XXXXX".

It's not a term I'm familiar with and I can't seem to find anything relevant in Italian on the internet. I thought perhaps it could be a heirarchy i.e. a "master or general mortgage" above the individual mortgage. Anyway, before going back to the client I wondered if anyone had come across it before and had any ideas.

Thanks,
Dominic