に至（いた）っては is an expression which presents the most extreme example for something from within a specific category. Due to this, it will usually be translated as 'when it comes to (A), (B)', 'in particular to (A) is (B)', or 'with (A) as the most extreme example, (B)'.
This is a combination of the case-marking particle に, the て-form of the る-Verb 至（いた）る 'to climax', or 'to culminate in', and the
adverbial particle は in its standard role of presenting a topic. In this way, the literal meaning of 'culminating within (A) is (B)' is quite close to the nuance of the English translations.
に至（いた）っては will appear following nouns, or nominalized phrases.
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私（わたし）の家族（かぞく）は全員（ぜんいん）機械音痴（きかいおんち）です。母（はは）に至（いた）ってはインターネットさえ使（つか）えないです。
My whole family is mechanically illiterate. What's more, my mother can't even use the internet.
最近（さいきん）ここにいる社員（しゃいん）みんなのやる気（き）がない。藤田（ふじた）さんに至（いた）ってはパソコンもつけていない。
Recently, employees here are unmotivated. As for Fujita-san, their computer isn't even turned on.
漢字（かんじ）テストは49点（てん）だった。リスニングに至（いた）っては20点（てん）だった。
My kanji test's score was 49. What's worse is that my listening score was 20.
As the verb 至（いた）る itself is used to present extreme examples or locations that are considered to be right 'on the precipice' of something,
に至（いた）っては will primarily present things that are surprising or astonishing in some way. This is primarily only used when the example itself is quite negative or unfavorable.
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あそこのお宅（たく）の次男（じなん）は留年（りゅうねん）するらしいですよ。長男（ちょうなん）に至（いた）っては学年（がくねん）トップだったらしいですよ。
I heard that the second son of the family over there flunked. As for their eldest son, I heard that he was at the top of his grade.