Is the MC aware of the rare medical condition prior to the story beginning?
If so the inciting incident would be the doctor giving him the choice to undertake the experimental procedure. His decision whether to undertake the procedure or not will be most of the action in act 2.

Or is the discovery of the rare medical condition in the story?
If so then the inciting incident would be him being told of his condition. His search for a cure would be most of the action the MC takes in act 2

Personally I find that decision making makes for poor action in a plot and action taken with out facing a decision with a good dilemma not compelling. Good plots force characters to make decisions (as McKee specifies under pressure) but this is to facilitate them taking action as a result not as a substitute for it.

Either way I think best to ask what would the MC have done with his life before the inciting incident then give him a choice to make and force him to take an action that is completely different to what he would have done otherwise.

Hope this helps.

Much better without the rats its shorter and describes the stakes and dangers in a more efficient way. It now sounds like a good concept for a low budget film.

After discovering the result of breathing the gas, what does she do? What does she want?

If you add these into the logline you can clarify whether this will be horror or thriller and have a really strong logline.

e.g:
After the contamination system locks a highly driven research assistant in an underground lab with her rival co-workers, she discovers the leaking gas induces psychopathic behavior and must fix the leak to save their lives.

or:
After the contamination system locks a highly driven research assistant in an underground lab with her rival co-workers, she discovers the leaking gas induces psychopathic behavior and must kill her infected colleagues to save her life.

Hope this helps.