The interface between Trs85 and Trs20 is quite conserved (Fig 3B) and involves Trs20 Asp46 (Fig 4E), a residue known to be important for assembly of both the TRAPPII and TRAPPIII complexes (Zong et al,2011; Brunet et al,2013; Taussig et al,2014) that is mutated in spondyloepiphyseal dysplasia tarda (SEDT) (Sacher et al,2019). Here, TRAPPC8 is linked to spondyloepiphyseal dysplasia tarda, X-linked.