Isaiah 7:8–9 (King James Bible) for the head of Syria is Damascus and the head of Damascus is Rezin … and the head of Ephraim is Samaria and the head of Samaria is Remaliah’s son
Here in 2 Nephi 17:8–9, we have two parallel couplets. The King James Bible has four instances of italicized is in this passage, but in the Book of Mormon text the second is is missing. We do not have the original manuscript for this passage, so it is difficult to determine whether is originally occurred before Rezin in the Book of Mormon text. It is quite possible that the omitted is simply represents a scribal error. But it is also possible that the current Book of Mormon text is correct since the is is missing before a single word (Rezin) and the resulting text seems to read quite well. Note, in this regard, that no printed edition of the Book of Mormon has ever supplied the is before Rezin. On the other hand, it would seem somewhat awkward if the parallel is in the second couplet (that is, the is that comes before the more complex Remaliah’s son) had been omitted.
Elsewhere in this long Isaiah quotation (2 Nephi 12–24), some examples of italicized is have been omitted and others have been kept. For examples of italicized is being omitted, see 2 Nephi 13:14. Here in 2 Nephi 17, we have another passage where italicized is has been retained (in this case, two times):
Since the omission of the second is in 2 Nephi 17:8–9 does work, the critical text will accept the reading of the earliest textual sources (namely, the is is omitted in only one case, before Rezin).
Summary: In 2 Nephi 17:8–9 we follow the earliest textual source (the printer’s manuscript) and accept the omission of is before Rezin.