Both STRUCTURE and principal component (PC) analyses showed the largest principal component differentiated northern from southern European ancestry.

A second PC further separated Italian, Spanish, and Greek from Ashkenazi ancestry as well as distinguishing among northern European populations.

In separate analyses of northern European participants … relationships were discerned showing a west to east gradient.

Application of this substructure information was critical … for rheumatoid arthritis in European Americans to reduce false positive signals.

… two sets of European substructure ancestry informative markers (ESAIM). The results … show that this information can be used …in association testing of candidate genes and in replication studies of WGA scans.

via PLOS Genetics: Analysis and Application of European Genetic Substructure Using 300 K SNP Information.