Hereditary fructose intolerance occurs in patients deficient in the enzyme fructaldolase B. Patients become symptomatic after eating foods containing fructose and/or sucrose.


Inheritance: autosomal recessive


Gene affected: ALDOB (aldolase B, fructose 1,6-bisphosphate aldolase) located at 9q21.3-q22.2.


This is a glycolytic enzyme that converts fructose 1,6-bisphosphate to glyceraldehydes-3-phosphate and dihydroxyacetone phosphate.


Types of mutation: missense mutations (A149P, A174D, N334K most common)


Clinical findings in infants following exposure to foods containing fructose or sucrose:

(1) poor feeding

(2) vomiting after eating

(3) incessant crying and irritability


Clinical findings in small children following exposure to foods containing fructose or sucrose

(1) sweating and trembling associated with hypoglycemia

(2) nausea and vomiting

(3) dizziness

(4) apathy, drowsiness or lethargy progressing to coma

(5) convulsions


Findings following continued exposure:

(1) hepatomegaly with jaundice, with steatohepatitis progressing to cirrhosis with hepatic failure

(2) hemorrhages

(3) proximal renal tubular dysfunction progressing to renal failure

(4) failure to thrive and poor growth

(5) diarrhea

(6) tremors and jerking

(7) edema and ascites

(8) rickets


Findings that may suggest the diagnosis:

(1) aversion to sweets and fruits

(2) unusual and seemingly bizarre eating habits

(3) onset of symptoms upon weaning from maternal breast milk

(4) absence of dental caries


As patients get older they tend to avoid foods that cause symptoms. Patients on a fructose and sucrose free diet are healthy.


A fructose breath test is available. In general, use of an oral or intravenous fructose loading test should be avoided since severe hypoglycemia and/or death have been reported.


If the diagnosis is in doubt, then molecular analysis of the ALDOB gene should be performed. Over 90% of mutations can be identified by a sequence analysis of exons 2-9 of the ALDOB gene.


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