に至っては picks out the most extreme case in a group: you describe a general situation, then name the one member where it goes furthest, "and as for X…". It follows a noun and takes the place of the topic は, and the case it picks out is usually the worst one.
The general statement comes first, as its own sentence or as a clause ending in が. Without it, に至っては has nothing to stand out from.
The extreme is usually a criticism, but it can be a strong point when the general statement is praise.
The two differ by one particle. に至っては singles out a member of a group. にいたって至って is about time: "only once it came to that".
に至っては is written and formal: essays, news commentary, speeches. In conversation, say なんか or とくに特に.