Linebreeding = Inbreeding
Inbreeding = Problems (Some you can see, cleft pallet,severly undershot,small litters, etc...)
(Some you will not see until its too late,trouble mating,trouble whelping,internal heart/liver/kidney problems)
IMO keep away from inbreeding, the KC have been practising this on terriers for over 100 years.
Look at the abortions they have created.
The KC hired a leader in the field of genetics to report on the state of their breeding policies.
They were not too happy when he came back and said they were wrong.