Hereditary fructose intolerance

Background

• Hereditary fructose intolerance (HFI) is an autosomal recessive disorder caused by deficiency of aldolase B, an enzyme essential for fructose metabolism in the liver, kidney, and intestine. When individuals with HFI ingest fructose, sucrose, or sorbitol, the toxic metabolite fructose-1-phosphate (F-1-P) accumulates, causing hypoglycemia, lactic acidosis, hepatic failure, and renal tubular dysfunction. HFI is entirely asymptomatic when fructose is avoided and potentially fatal when it is not.
• The emergency physician encounters HFI as an infant with vomiting, hypoglycemia, and liver failure temporally related to the introduction of weaning foods, or as a known HFI patient with accidental fructose exposure.
• Autosomal recessive; prevalence approximately 1 in 20,000-30,000 live births; carrier frequency ~1 in 70
• Caused by mutations in the ALDOB gene (chromosome 9q22.3); most common mutations are A149P, A150P, and A174D
• Symptoms only occur after ingestion of fructose, sucrose, or sorbitol — patients are completely well on a fructose-free diet
• Typically presents at 4-6 months of age when weaning foods (fruits, vegetables, sweetened cereals, juices) are introduced
• Breastfed infants are protected — breast milk contains lactose (glucose + galactose) but no fructose; symptoms begin when breast milk is supplemented or weaning starts
• Deaths occur primarily from diagnostic delay — once recognized, the treatment (dietary fructose avoidance) is simple and completely effective

Mechanism

• Fructose is phosphorylated by fructokinase → fructose-1-phosphate (F-1-P)
• Aldolase B normally cleaves F-1-P → glyceraldehyde + dihydroxyacetone phosphate (enter glycolysis/gluconeogenesis)
• In HFI: aldolase B is absent or deficient → F-1-P accumulates → multiple downstream effects:
  • Intracellular phosphate trapping: F-1-P sequesters inorganic phosphate (Pi) → depletion of ATP
  • Hypoglycemia: F-1-P inhibits both glycogenolysis (glycogen phosphorylase) AND gluconeogenesis (glucose-6-phosphate isomerase) — a dual block on glucose production
  • Glucagon resistance: hypoglycemia in HFI does NOT respond to glucagon (because glycogenolysis is blocked)
  • Lactic acidosis: F-1-P activates pyruvate kinase → increased lactate production
  • Hyperuricemia: ATP depletion → AMP degradation → increased urate production
  • Hepatocellular and renal tubular toxicity: direct cytotoxic effects of F-1-P accumulation → liver failure, Fanconi syndrome

Key dietary sources of fructose (EM-relevant)

• Fruits (all), fruit juices, honey
• Sucrose (table sugar) — sucrose = glucose + fructose; present in nearly all sweetened foods, candy, cookies, soft drinks
• Sorbitol — sugar alcohol used as sweetener in "sugar-free" products; also found in many medications (syrups, elixirs, chewable tablets) — a critical hidden source
• High-fructose corn syrup — ubiquitous in processed foods
• Many vegetables contain small amounts of fructose (especially peas, sweet corn, sweet potato)
• IV fructose or sorbitol solutions (historically used in some parenteral nutrition formulations — now rarely used but must be actively avoided)

Clinical features

Acute presentation (the ED encounter)

Infant with new diagnosis (classic presentation)

• Previously healthy breastfed infant, 4-6 months old
• Symptoms begin within minutes to hours of ingesting fructose-containing food or formula for the first time
• Vomiting (often violent/repeated)
• Profound hypoglycemia (lethargy, seizures, diaphoresis, pallor)
• Abdominal pain/distress
• Poor feeding, irritability
• With continued fructose exposure:
  • Hepatomegaly (progressive)
  • Jaundice (conjugated hyperbilirubinemia)
  • Coagulopathy (elevated INR — hepatic synthetic failure)
  • Bleeding (GI hemorrhage, oozing from puncture sites)
  • Ascites, edema
  • Renal tubular dysfunction (Fanconi syndrome: glycosuria, aminoaciduria, phosphaturia, metabolic acidosis)
  • Failure to thrive
  • Seizures, coma, death — in severe untreated cases

Known HFI patient with accidental exposure

• Acute episode after accidental ingestion of fructose-containing food or medication
• Rapid-onset vomiting, hypoglycemia, malaise
• May be mild (self-limited vomiting) or severe (hypoglycemia, acidosis, liver decompensation) depending on fructose load

Diagnostic clues

• Temporal relationship to food introduction: symptoms began when weaning started or when a new food/formula containing fructose or sucrose was introduced
• Aversion to sweets: older children and adults with undiagnosed HFI develop a strong natural aversion to sweet foods and fruits — this is a classic historical clue
• Absence of dental caries: lifelong fructose avoidance results in remarkably healthy teeth — another diagnostic pearl
• Symptoms resolve completely when fructose is removed from the diet

Differential diagnosis

Infant with vomiting, hypoglycemia, and liver failure

• Galactosemia — very similar presentation but triggered by lactose/galactose (present in breast milk and standard formula); E. coli sepsis association; cataracts; reducing substances in urine
• Tyrosinemia type 1 — liver failure + coagulopathy + very high AFP; boiled cabbage odor; Fanconi syndrome; not temporally related to specific food introduction
• Sepsis — ill-appearing; fever; positive cultures
• Neonatal hepatitis (other causes)
• Neonatal hemochromatosis (GALD) — presents at birth, not at weaning
• Glycogen storage diseases — hepatomegaly + hypoglycemia; not food-specific
• Fructose-1,6-bisphosphatase deficiency — similar presentation (hypoglycemia + acidosis + hepatomegaly) but triggered by fasting rather than fructose ingestion; important to distinguish
• Urea cycle defects, organic acidemias
• Food protein-induced enterocolitis syndrome (FPIES) — profuse vomiting after specific food; no hypoglycemia or liver disease

Key distinguishing features of HFI

• Symptoms temporally linked to fructose/sucrose introduction
• Hypoglycemia that does NOT respond to glucagon
• Hypophosphatemia (phosphate trapping by F-1-P) — relatively specific finding
• Hyperuricemia — unusual in an infant; should raise suspicion
• Resolution with fructose withdrawal

Evaluation

ED workup

• Blood glucose: expect hypoglycemia (may be severe/refractory)
• BMP: hypophosphatemia (characteristic), metabolic acidosis, elevated creatinine (if renal involvement)
• Hepatic panel: elevated AST/ALT (hepatocellular injury); elevated bilirubin (conjugated)
• Coagulation studies: elevated PT/INR (hepatic synthetic failure in severe cases)
• Uric acid: hyperuricemia (ATP depletion → AMP breakdown → urate production)
• Lactate: lactic acidosis
• Magnesium: hypermagnesemia (released from damaged cells with ATP depletion)
• CBC: thrombocytopenia (in severe hepatic failure)
• Urinalysis: glycosuria (normal blood glucose), aminoaciduria, phosphaturia (Fanconi pattern); fructosuria may be present
• Ammonia: may be elevated in severe hepatic failure
• AFP: may be elevated (liver injury; less markedly than tyrosinemia)

Characteristic laboratory constellation

Hypoglycemia + hypophosphatemia + hyperuricemia + lactic acidosis + liver dysfunction in an infant following fructose exposure = highly suspicious for HFI

Confirmatory testing (arrange via specialist)

• ALDOB gene sequencing: preferred confirmatory test; noninvasive; high sensitivity and specificity
• Liver biopsy: for aldolase B enzyme activity measurement — invasive; reserved for cases where genetic testing is inconclusive
• Fructose tolerance test: NO LONGER RECOMMENDED — dangerous; causes profound hypoglycemia and can precipitate acute liver failure
• Urine reducing substances: may be positive (fructosuria) after fructose ingestion; non-specific
• Carbohydrate-deficient transferrin (CDT): often abnormal in untreated HFI (secondary glycosylation defect)

Management

Acute emergency management

• Stop all fructose, sucrose, and sorbitol intake immediately — this is the single most important intervention
• IV dextrose (D10W): correct and prevent hypoglycemia with glucose-containing fluids only
  • Do NOT give fructose or sorbitol-containing IV solutions
  • Do NOT give sucrose-containing oral medications
• Correct metabolic acidosis: sodium bicarbonate if pH <7.1 or bicarbonate severely depressed; often improves with dextrose and fructose withdrawal
• Correct coagulopathy: vitamin K, FFP if active bleeding
• Treat hepatic failure per standard protocols (see Acute liver failure)
• Monitor and correct electrolytes: phosphate supplementation if severely hypophosphatemic; monitor potassium, magnesium
• Glucagon is NOT effective for hypoglycemia in HFI — both glycogenolysis and gluconeogenesis are blocked by F-1-P; give IV dextrose instead

Medication safety — critical for the EM physician

• Many common pediatric liquid medications contain sorbitol or sucrose as sweeteners — these are dangerous in HFI
• Before administering ANY oral medication to a known or suspected HFI patient, check the excipient/inactive ingredient list for fructose, sucrose, or sorbitol
• Safer alternatives: use tablet formulations (crushed if needed), or IV formulations
• Common offenders: acetaminophen syrups, ibuprofen suspensions, antibiotic suspensions, cough syrups, chewable tablets
• Consult pharmacy to verify medication safety

Long-term management (arrange via metabolic specialist)

• Lifelong strict dietary exclusion of fructose, sucrose, and sorbitol — this is the definitive and only treatment
• Nutritionist referral — extensive dietary education required; hidden fructose sources are ubiquitous
• Vitamin and mineral supplementation — patients on fructose-free diets may develop deficiencies in vitamin C, folate, and fiber (from restricted fruit/vegetable intake)
• Life expectancy is completely normal with dietary compliance
• No liver transplant required (unlike tyrosinemia type 1 or Crigler-Najjar syndrome)

Disposition

• Infant with suspected new diagnosis (vomiting + hypoglycemia + liver dysfunction after fructose introduction):
  • Admit
  • Stop all fructose/sucrose/sorbitol sources
  • IV dextrose, supportive care
  • Metabolic/genetics consultation
  • Arrange ALDOB gene testing
• Known HFI patient with mild accidental exposure (vomiting, mild hypoglycemia, no liver failure):
  • Treat hypoglycemia with oral glucose or IV dextrose
  • Observe until asymptomatic and blood glucose stable
  • May discharge if well, tolerating fructose-free diet, glucose stable, and family is reliable
• Known HFI patient with severe exposure (liver failure, refractory hypoglycemia, acidosis):
  • Admit (PICU if critically ill)
  • Aggressive IV dextrose, correct acidosis and coagulopathy
  • Metabolic team consultation
• Ensure all families receive:
  • Written dietary guidance (fructose, sucrose, sorbitol avoidance)
  • Medical alert identification for the child
  • Guidance on medication safety (sorbitol in syrups)
  • Metabolic specialist follow-up

See Also

• Galactosemia
• Tyrosinemia
• Fanconi syndrome
• Neonatal hepatitis
• Acute liver failure
• Hypoglycemia
• Neonatal hemochromatosis

External Links

• StatPearls — Hereditary Fructose Intolerance
• StatPearls — Fructose-1-Phosphate Aldolase Deficiency
• World J Clin Pediatr — Hereditary fructose intolerance: A comprehensive review (2022)
• Diseases — Clinical Practice Guidelines for HFI (2024)
• Orphanet — Hereditary fructose intolerance