Mutations of the human GDP-fucose transporter gene SLC35C1 cause the rare disease leukocyte adhesion deficiency type 2 (LAD II), or congenital disorder of glycosylation SLC35C1-CDG, characterized by severe immunodeficiency, psychomotor defects, delayed mental development, and slow growth (11, 12, 13, 14, 15, 16). Here, SLC35C1 is linked to Immunodeficiency.