DHDDS and cystic kidney disease: Biliary duct abnormalities have also been observed in patients with mutations in mannose‐6‐phosphate isomerase (MPI), which interconverts fructose‐6‐phosphate to mannose‐6‐phosphate.23 Sabry et al24 reported a dehydrodolichyl diphosphate synthase (DHDDS‐CDG) patient with dilations of the biliary duct and renal failure, and Schenk et al7 reported renal cysts in a MPDU1‐CDG patient with the same G73E substitution.