Question

Will just taking out the "it" make this sentence correct?
The disease is typified by a delay in motor development, by self-destructive behavior, and it leads to death.

Answer 1

No, in order to make the series' elements parallel, you need a third phrase that starts with "by" and ends with a prepositional phrase ... so you have this:

... by a delay ..., by self-destructive behavior, and by ________________.

How will you rephrase the last part of this sentence?

Answer 2

and by death.

Answer 3

Yes, that works. Good!