Both Ephesians 5:31 and Matthew 19:5 quote Genesis 2:24:
'For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh.'
However in Matthew Jesus uses the Greek word heneka, whereas in Ephesians the word anti is used instead.
There appears to be no difference in the English translations, and the change seems inconsequential to an understanding of the English text. Considering it is a direct quote, there doesn't appear to be a reason to change the word at all, and yet it was changed.
Is there a reason, possibly related to grammar, syntax or dialect, governing the use of a different Greek word (anti) for this phrase in Paul's direct quotation of scripture that was not present either in the original text or in Matthew (or vice versa)?
Gen 2:24 ἕνεκεν τούτου καταλείψει ἄνθρωπος τὸν πατέρα αὐτοῦ καὶ τὴν μητέρα αὐτοῦ καὶ προσκολληθήσεται πρὸς τὴν γυναῖκα αὐτοῦ, καὶ ἔσονται οἱ δύο εἰς σάρκα μίαν. The Septuagint (LXX), edited by Alfred Rahlfs. Published in 1935; public domain.
Westcott and Hort / [NA27 variants] Matthew 19:5 καὶ εἶπεν Ἕνεκα τούτου καταλείψει ἄνθρωπος τὸν πατέρα καὶ τὴν μητέρα καὶ κολληθήσεται τῇ γυναικὶ αὐτοῦ, καὶ ἔσονται οἱ δύο εἰς σάρκα μίαν;
Westcott and Hort / [NA27 variants] Ephesian 5:31 ἀντὶ τούτου καταλείψει ἄνθρωπος τὸν πατέρα καὶ τὴν μητέρα καὶ προσκολληθήσεται πρὸς τὴν γυναῖκα αὐτοῦ, καὶ ἔσονται οἱ δύο εἰς σάρκα μίαν.