I am the PA for both the St. John and Sension Family DNA Projects with FTDNA. We have been able to ascertain that Normandy has a genetic history with the Celts as well as Scandinavia.
We also know that Scandinavia has a genetic relationship with the Celts at about a 50:50 ratio.
It is not settled as to what the Nordic Genetic haplotype is. With that said, there are two genetic splits within the St. John Family. The first, having a documented and proven lineage with the Aristocratic Family has what we think is the typical Nordic Haplotype.
The second family , that of Matthias, bears the Celtic haplotype. Don't think Irish, as one would be inclined to do- but think North Eastern Europe, such as Austria/ Germany for origins dating back 5000 years ago.