One of the most puzzling questions of the MCU is how Age of Ultron's Maximoff Twins survived the HYDRA enhancement experiments while everyone else died. The answer involves genetics, seeing as how they are brother and sister , their must be something in their genetic code that allowed them to withstand the Mind Stone's cosmic radiation and gain powers. But what is in their genetic code that allowed them to gain their powers?
The only other instance in the MCU where a select few survive and gain powers, while others die is the Inhuman's touching the Diviner in Agents of S.H.I.E.L.D. . The Diviner would scan the subjects genetic code and if it they were of Inhuman blood they would be spared. This led to fan speculation that the twins were Inhumans instead of Mutants for the MCU. However the Inhuman Lincoln Campbell was subjected to the same experiments the twins were, and he would have died in the processs if not for Quake . My guess is Lincoln nearly died because the Inhuman DNA from his original ancestor whom was experimented by the Kree was repressing. In the comics the reason that the Inhumans from Attilan were so powerful is because they breed among their own kind for generations so that their powers would not decrease due to human DNA interference. So if the twins were Inhumans then they would have been Inhuman's that have been reduced in power due to the countless centuries of genetic supression, and probably would have died in the process like Lincoln nearly did. But the twins do posseses the Inhuman capabilites to gain power after exposure to certain energies. This could mean that the twins came from Attilan itself, unfortunately it did not seem as if their family had any knowledge of Inhumans prior to their transformation. This has led me to the assumption that the twins were born human, however at some point before HYDRA they would be introduced to Inhuman DNA which would be bonded to theirs. But who has the technology or the knowledge to perform such a experiment?
There is one earth bound geneticist in the Marvel Comics Universe who is skilled enough enough at genetic manipulation to give ordinary humans the potential to develop superpowers, and has a history with the Maximoff's.
The HIGH EVOLUTIONARY !
Earlier this year the true origins of the Scarlet Witch and Quicksilver was revealed in Uncanny Avengers#4. In the comic the villain the High Evolutionary explains that Magneto, aka Max Eisenhardt, was never their father, and they do not carry the mutant gene. The High Evolutionary himself claims responsibility for giving them their powers, as part of his eternal search for genetic perfection.
In the Comics the High Evolutionary aka Herbert Wyndham was a geneticist from the 20th century who after meeting an Inhuman from Attilan was given the keys to genetic expansion. Using the tools he received Herbert began a mission to evolve humanity to perfection. He developed a suit of armor for himself that could evolve his body to the brink of the human condition, which gave him a wide variety of superpowers. During the course of the comics, the High Evolutionary has encountered Thor, Spider Man, and even the Avengers!
Given that the High Evolutionary used Inhuman based DNA and technology to advance his research in the comics, then if he will be apart of the MCU it stands to reason that he would use Inhuman resources to advance his research.
Perhap's in adaption to the MCU, the High Evolutionary initially tried to give the twins powers by adding Inhuman DNA into their genetic code thus turning them into some kind of Artificial Inhumans, thus giving them the potential to develop powers similar to Inhumans, but without Terrigen Crystals couldn't finish the job. So as a result he would then return them to their family, where they would then grow up in Sokovia, lose their parents, and finally volunteer for HYDRA tests and gain powers.
This could prove the answer as to how the Twins survived the experiments performed by HYDRA, and maybe even if they will have strong ties to Inhuman's in the future. It could also be the opportunity to use a character who could fill the gap left by both Magneto and Apocalypse, as both characters work to bring powered individuals to their rightful place as rulers of the world. The High Evolutionary could definitely fill that role, he certainly has the power to lead and the scientific knowledge to create an army, yet his interest in animals may need to be modified a little. He is so powerful that he has been known to go toe to toe not only with Apocalypse, but even Galactus himself.