We have previously shown that the putative mammalian retromer components sorting nexins 1 and 2 ( Snx1 and Snx2 ) result in embryonic lethality when simultaneously targeted for deletion in mice, whereas others have shown that Hβ58 (also known as mVps26 ), another retromer component, results in similar lethality when targeted for deletion. In the current study, we address the genetic interaction of these mammalian retromer components in mice. Our findings reveal a functional interaction between Hβ58, SNX1, and SNX2 and strongly suggest that SNX2 plays a more critical role than SNX1 in retromer activity during embryonic development. This genetic evidence supports the existence of mammalian retromer complexes containing SNX1 and SNX2 and identifies SNX2 as an important mediator of retromer biology. Moreover, we find that mammalian retromer complexes containing SNX1 and SNX2 have an essential role in embryonic development that is independent of cation-independent mannose 6-phosphate receptor trafficking.