Is the population of Sado Island genetically close to the population of western Japan?

To explore the effect of aging, a cohort study is being performed on Sado Island, which is located in the Sea of Japan. Sado Island is close to the eastern coast of Japan, yet its population speaks the western Japanese dialect. Consequently, the genetic background of the population of Sado Island is of interest. Based on Nei's genetic distance, we compared the allele frequencies of people from Sado Island to those of people from Nagahama and Miyagi, which are located in the western and northeastern parts of Honshu, respectively. The results showed that the populations of Miyagi and Nagahama are genetically closer to each other than to the population of Sado Island. Because the Sado and Honshu Islands are isolated by a channel, it is possible that genetic drift occurred within Sado Island, which would explain the uniqueness of the people of this region.