In the near future, some girls are born mutated. Known as Diclonius, this new species is believed to have been chosen by God to wipe out mankind. Unlike regular humans, Diclonius have two horns on their head and ‘vectors' - invisible ‘hands.' Contained within a research facility unknown to the world, the Diclonius are experimented upon mercilessly; many die or develop a hate for mankind. One such creature, Lucy, is said to be the first of the Diclonius. She escapes from the facility, but while fleeing she takes a bullet to the head and is seemingly killed. However, it seems Lucy isn't quite dead yet; she's instead developed an alternate personality called Nyuu. She's washed up on a shore where two people, Kouta and Yuka, find her and bring her home, unaware that such a monster still lurks within Nyuu.
Variante has a female protagonist: with more power than she realizes, goes through alot of emotional breakdowns, stories can't be called original, but they are done well.
Difference is, Variante is short, sweet, to the point, REALLY keeps you in suspence, and doesn't use fan service to keep people interested. Both are good manga of course :)
Franken Fran, creation of the absent Professor Madaraki, has a true gift when it comes to the scalpel: she can give you the perfect body, bring the dead to life or stitch people together so that they will never again be apart. Join Fran and her boy-headed cat as they learn about the human soul while carving up the human flesh. But ethics aside, can something beautiful come out of such ugly work, or is it doomed to remain ugly until the end? On the other hand, does it matter?
In secret, alien parasites drift downwards toward Earth. Their directive: to take control of a human body and thrive in secret. When a parasite attempts to take over Shinji, an ordinary high school student, he stops it in his arm to save his mind. With the strange power of amorphous muscle, the curious parasite strikes an uneasy truce with Shinji: it will keep him alive and strong so that it may continue living, and will help protect him from the other parasites that might not take kindly to Shinji's mind still actively working. Can Shinji gain the courage to face the parasites and protect humanity? And would it even make a difference if he did?
Humans who change into grotesque monsters? Checked.
Protagonist who has a monstrous arm that goes out of control? Checked.
Horror with lots of gore? Double checked.
As you can see those two manga share quite a number of similarities, so there is a good chance you might like one if you liked the other.
P.S. I got the impression that Variante is even more disturbing than Parasyte.