に至っては is used to single out an extreme or most notable case from a broader context, often to emphasize that the situation is particularly bad (or occasionally remarkable). It translates roughly as "when it comes to," "as for (in particular)," or "what is worse/more." The speaker first describes a general situation, then uses に至っては to highlight the most extreme example within that situation.
The most common use of に至っては is to point out that among several bad or noteworthy things, one case stands out as the worst or most extreme.
The structure typically follows this flow:
While にいたる至るまで means "all the way to / up to" and covers a range, に至っては specifically picks out one extreme case for commentary. Do not confuse the two.
に至っては is a formal, written-style expression. It is commonly found in essays, news commentary, and formal speeches. While it most often highlights something negative, it can occasionally be used for positive extremes if the context supports it.