An unspliced form of SFRP1 is the dominant form in the lung and liver, leading to an extended protein.  This extended sequence contains a hydrophobic region that may act as a transmembrane anchor, modifying the localization of the protein.  This may then influence the function of SFRP1 in different tissues because an untethered protein may be more effective in antagonizing Wnt signaling to tumor cells than would a membrane-bound form.