Speculation that the Ashkenazi arose from Khazar stock surfaced in the later 19th century and has met with mixed fortunes in the scholarly literature. In late 2012 Eran Elhaik, a research associate studying genetics at the Johns Hopkins University School of Public Health, argued for Khazar descent in his paper The Missing Link of Jewish European Ancestry: Contrasting the Rhineland and the Khazarian Hypotheses. A 2013 study of Ashkenazi mitochondrial DNA found no significant evidence of Khazar contribution to the Ashkenazi Jewish DNA, as would be predicted by the Khazar hypothesis.
What did a 2013 study of Ashkenazi mitochondrial DNA find in regards to the Khazar descent idea?
no significant evidence of Khazar contribution to the Ashkenazi Jewish DNA