Pancytopenia from severe cobalamin (Vitamin B12) deficiency in Johanson-Blizzard syndrome

摘要

Johanson-Blizzard syndrome is a rare autosomal recessive disorder characterized by nasal, auditory and dental abnormalities, and exocrine pancreatic insufficiency. These patients require oral pancreatic enzyme replacement and fat-soluble vitamin supplements.Cobalamin (vitamin B_(12)) is essential for several important enzymatic processes in the body that lead to energy metabolism, DNA synthesis and blood cell production. Patients with cobalamin deficiency can develop hematological and neuropsychiatric abnormalities. Absorption of cobalamin is complex. Two distinct cobalamin-binding proteins haptocorrin (R binder) and intrinsic factor (IF) compete for free cobalamin released in the stomach. In the acidic environment, haptocorrin binds free cobalamin with much greater affinity than IF. Pancreatic enzymes degrade the haptocorrin-cobalamin complex in the small intestine, releasing free cobalamin to bind to IF for its eventual absorption in the terminal ileum.3 Cobalamin deficiency can occur rarely in patients with exocrine pancreatic insufficiency (for example, cystic fibrosis), although the precise mechanisms remain unclear. We report this complication occurring in Johanson-Blizzard syndrome.