Most common causes:
Severe malabsorption (e.g. cystic fibrosis, celiac sprue, pancreatic insufficiency)
Abetalipoproteinemia (genetic disorder)
Chronic cholestatic liver disease (e.g. biliary atresia)
Severe malabsorption (e.g. cystic fibrosis, celiac sprue, pancreatic insufficiency)
Abetalipoproteinemia (genetic disorder)
Chronic cholestatic liver disease (e.g. biliary atresia)
Vitamin E deficiency
Vitamin A deficiency
Vitamin A toxicity
Vitamin B deficiencies
Vitamin B1 deficiency 
Vitamin B9 deficiency
Beriberi
Vitamin B7 deficiency