According to Frank, during detailed research he was able to unearth some circumstantial evidence that made these rumors appear not entirely unreasonable: Hitler's grandmother Anna Maria Schicklgruber worked as a housemaid or cook in the house of a Jew from Graz named Frankenberger in the 1830s.
The column for the child's father was left blank in the baptismal register, but Anna Maria Schicklgruber received financial support from Frankenberger for the next 14 years.
The same is true for the similarly named Bohemian town Gratzen (now Nové Hrady, Czech Republic) which is closer to Schicklgruber's native region.
As early as 1956, Franz Jetzinger, author of Hitler’s Youth, pointed out that "the name Frankenberger [...] does not sound Jewish at all" and that it must therefore "first be proven" that Frankenberger—even if he was actually the father of Alois Hitler—actually was a Jew.
"[9] Brigitte Hamann, on the other hand, wrote that "here the angry anti-Semite Frank wanted to blame the hated Jews for an allegedly Jewish Hitler and unsettle them with rumours".
[10] Notable historians who dismiss the thesis are Ian Kershaw,[11] Robert Payne,[12] Walter Görlitz,[13] Anton Joachimsthaler,[14] Christian Graf von Krockow,[15] John Toland,[16] Brigitte Hamann[10] and Ernst Deuerlein.
[17] Apart from serious historical research, the "revelation" of Hitler's "Jewish descent" has been taken up again and again by publications with a popular scientific, conspiracy theory or sensationalist impact.
It is characteristic of this literature, which is almost unmanageable in its breadth, that it attempts to present source material that has been known for decades, in particular Frank's rumours, as new knowledge and in doing so fails to mention the continuous and almost unanimously skeptical and negative reception by the leading Hitler biographers.
Sax points out that many Jews lived in places without official sanction and demonstrated the existence of a settled Jewish community in Graz before the law formally permitted their residence, saying that "Contemporary historians have largely dismissed Frank's claim, primarily on the grounds that there were purportedly no Jews living in Graz in 1836, when Hitler's father Alois Schicklgruber was conceived.
In this paper, evidence is presented that there was in fact 'a small, now settled community' (eine kleine, nun angesiedelte Gemeinde)—of Jews living in Graz before 1850."