I have heard this before but looks like genetic testing is finally shedding some light on that idea. Heidi Blake writes on the Telegraph:
Saliva samples taken from 39 relatives of the Nazi leader show he may have had biological links to the “subhuman” races that he tried to exterminate during the Holocaust. Jean-Paul Mulders, a Belgian journalist, and Marc Vermeeren, a historian, tracked down the Fuhrer’s relatives, including an Austrian farmer who was his cousin, earlier this year.
A chromosome called Haplogroup E1b1b1 which showed up in their samples is rare in Western Europe and is most commonly found in the Berbers of Morocco, Algeria and Tunisia, as well as among Ashkenazi and Sephardic Jews.
“One can from this postulate that Hitler was related to people whom he despised,” Mr Mulders wrote in the Belgian magazine, Knack. Haplogroup E1b1b1, which accounts for approximately 18 to 20 per cent of Ashkenazi and 8.6 per cent to 30 per cent of Sephardic Y-chromosomes, appears to be one of the major founding lineages of the Jewish population.
Read More: Telegraph