Viking blood, blue eyes and other risk factors for Dupuytren's

What is the actual story of the Vikings and Dupuytren's? The full history will never be known, but some fascinating details on this and other risk factors, including blue eyes, are reviewed here: http://www.dupuytrenfoundation.org/DupPDFs/2001_Flatt_1397.pdf. See page 4 for a decision tree showing how to predict the risk of recurrence after surgery based on family history, bilaterality, age of onset and involvement of other areas.