The human gene SLC35A1 encodes the CMP-sialic acid transporter which mediates the antiport of CMP-sialic acid (CMP-Neu5Ac) into the Golgi lumen in exchange for CMP (Ishida et al. 1996). Defects in SLC35A1 are the cause of congenital disorder of glycosylation type 2F (CDG2F; MIM:603585), characterised by under-glycosylated serum proteins. CDGs are a family of severe inherited diseases caused by a defect in protein N-glycosylation. These multisystem disorders present with a wide spectrum of phenotypes such as disorders of nervous system development, psychomotor retardation, dysmorphic features, hypotonia, coagulation disorders and immunodeficiency (Martinez-Duncker et al. 2005, Song 2013).