SNX21 and glycogen storage disease VI: In the present study we have used unbiased quantitative proteomics to define those proteins that associate with SNX21, revealing that the SNX21 N-terminal extension interacts with the Huntington's disease protein huntingtin (Htt) (Saudou and Humbert, 2016) whereas the PXB domain appears to associate with various members of the septin family of cytoskeletal- and membrane-associated proteins (Mostowy and Cossart, 2012): an interaction that is also observed in SNX20.