COG5 and microcephaly: Cells: reduction in STX6 levels, glycosylation defects including reduced sialyation of O‐glycans; decreased activity of B4GALT1 but normal import of UDP‐galactose into the Golgi, reduced protein levels of COG5 (55%), COG6 (21%), and COG7 (62%), degradation of mRNA encoding COG6, formation of the COG complex affectedPatients: microcephaly, chronic inflammatory bowel disease, micronodular liver cirrhosis, severe neurologic disease characterized by vitamin K deficiency, vomiting, intractable focal seizures, intracranial bleedings and fatal outcome in early infancy