How does the sign of four relate to frankenstein by mary shelley?

I do not see a relationship between Frankenstein and Doyle's The Sign of Four. If you find something, please come back and let me know..... I'd be very interested in the result.

The setting of Pondicherry Lodge is a good example of one from the Gothic horror genre, which Frankenstein is classed as a member of. Pondicherry Lodge is shrouded in mystery with its foreboding and ominous appearance created through the use of negative and rather creepy adjectives, such as "damp fog", "broken glass" and "iron-clamped door." Other typical features of the Gothic horror genre are also shown through: the fact that the company arrive at the lodge (chapter 5) late at night; there is only "half a moon"; and the lodge itself is isolated within its "very high stone wall." Conan Doyle further develops this gothic feel throught the use of noun phrases, such as, "desolate grounds" and "deathly silence", which also hints to the deathly silence that Thaddeus Sholto, Holmes and the others encounter when they enter Bartholomew's chamber. The reasons behind why Bartholomew's laboratory is in his room, or even why he has a laboratory in the first place, are never explained, however this seems to echo Frankenstein's famous laboratory.