Hereditary fructose intolerance

Hereditary fructose intolerance (HFI) or fructose poisoning is a hereditary condition caused by a deficiency of liver enzymes that metabolise fructose.

Causes
The deficient enzyme is aldolase-B, which converts fructose-1-phosphate to DHAP and glyceraldehyde. This means that the fructose cannot be further metabolised beyond fructose-1-phosphate. This traps phosphates; which are needed to phosphorylate glycogen phosphorylase which carries on to release units of glucose-1-phosphate from glycogen. (Glucose-1-phosphate gets converted to glucose-6-phosphate and then dephosphorylated to form glucose).

In addition, aldolase-B plays an important role in gluconeogenesis, producing fructose-1,6-bisphosphate from glyceraldehyde-3-phosphate and DHAP. Thus, glucose cannot be released through the breakdown of glycogen nor can it be synthesized from gluconeogenesis, resulting in severe hypoglycaemia.

Presentation
If fructose is ingested, other symptoms such as vomiting, hypoglycemia, jaundice, hemorrhage, hepatomegaly, hyperuricemia and eventually kidney failure will follow.

Treatment
Treatment is with a fructose free diet, which if adhered to, is concordant with a good prognosis.

Fructose and sucrose eliminated from diet.

Related conditions
Hereditary fructose intolerance should not be confused with fructose malabsorption. The latter is the same as dietary fructose intolerance (DFI), a deficiency of fructose transporter enzyme in the enterocytes, which leads to abdominal bloating, diarrhea and/or constipation.