Hereditary Fructose Intolerance (HFI), the ALDOB Gene, and Factor V Leiden

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Introduction

Hereditary Fructose Intolerance (HFI) is a rare inherited metabolic disorder caused by disease-causing mutations in the ALDOB gene. Individuals with HFI are unable to properly break down fructose, resulting in the accumulation of toxic metabolites that can damage the liver, kidneys, and other organs. Symptoms often begin in infancy when fructose-containing foods are introduced into the diet.

With the increasing popularity of direct-to-consumer genetic testing, many people discover variants in the ALDOB gene, including markers such as i5012665, which corresponds to rs387906225 (Delta4E4). 

Causes of HFI

Hereditary fructose intolerance is caused by mutations in the ALDOB gene, which encodes the enzyme fructose-1-phosphate aldolase B. Depending on the type of mutation, enzymatic activity can be reduced by 85% to 100%.

Some individuals also learn they carry Factor V Leiden, a separate inherited genetic condition associated with increased blood clotting risk. Although both conditions are genetic, they affect entirely different biological systems.

Indications for Testing

According to the College of American Pathologists (CAP) Consensus Conference Statement, testing for Factor V Leiden is recommended in patients with a personal or family history suggestive of inherited thrombophilia.

Genetics of HFI

The ALDOB gene, located on chromosome 9, provides instructions for producing aldolase B, an enzyme essential for fructose metabolism in the:

  • Liver
  • Kidneys
  • Small intestine

Under normal circumstances, aldolase B breaks down fructose-1-phosphate into compounds that can be used for energy production. In individuals with HFI, mutations in ALDOB reduce or eliminate aldolase B activity, causing fructose-1-phosphate to accumulate inside cells.

More than 50 pathogenic ALDOB mutations have been identified. Among the most common are:

  • A149P
  • A174D
  • N334K

Targeted genetic tests for these variants identify approximately 87% of HFI cases in many European populations.

The i5012665 Marker (rs387906225)

One variant that appears in some consumer DNA reports is i5012665, corresponding to rs387906225, also known as Delta4E4.

Depending on the specific genotype, this marker may indicate:

  • A typical genotype
  • Carrier status
  • The need for further clinical evaluation

Because insertion/deletion variants can be reported differently by testing companies, interpretation should be confirmed through clinical-grade genetic testing.

Inheritance Pattern

HFI follows an autosomal recessive inheritance pattern.

This means:

  • An affected individual inherits two pathogenic ALDOB variants, one from each parent.
  • Individuals with one altered copy are considered carriers.
  • Carriers are usually asymptomatic.

When both parents are carriers:

  • 25% chance of an affected child
  • 50% chance of a carrier child
  • 25% chance of a child without the mutation

Causes of HFI

HFI is caused by mutations in the ALDOB gene, which encodes the enzyme fructose-1-phosphate aldolase B. Depending on the mutation, enzyme activity may be reduced by approximately 85% to nearly 100%.

As a result, fructose metabolism becomes blocked after consumption of:

  • Fructose
  • Sucrose (table sugar)
  • Sorbitol

The accumulation of fructose-1-phosphate disrupts cellular energy production and glucose regulation, leading to the characteristic symptoms of HFI.

Symptoms of Hereditary Fructose Intolerance

Symptoms typically appear during infancy when fructose-containing foods are introduced.

Acute Symptoms

Shortly after fructose ingestion, affected individuals may experience:

  • Nausea
  • Recurrent vomiting
  • Severe abdominal pain
  • Sweating
  • Lethargy
  • Tremors
  • Hypoglycemia (low blood sugar)
  • Seizures
  • Coma in severe cases

Hypoglycemia is one of the most dangerous complications and may become life-threatening if untreated.

Chronic Symptoms

Repeated fructose exposure can result in:

  • Hepatomegaly (enlarged liver)
  • Jaundice
  • Chronic liver dysfunction
  • Failure to thrive
  • Growth restriction
  • Kidney dysfunction
  • Renal tubulopathy
  • Lactic acidosis

Natural Food Aversion

Many individuals with HFI develop a strong dislike of:

  • Sweets
  • Fruit
  • Sugary drinks
  • Desserts

This instinctive avoidance is believed to be protective because fructose ingestion consistently produces unpleasant symptoms.

Variation in Food Tolerance

Tolerance can vary among individuals. Some people report that:

  • Apples trigger symptoms more readily than other fruits
  • High fructose corn syrup causes significant reactions
  • Sugar snap peas are particularly problematic
  • Certain citrus fruits may be better tolerated

Differences in fructose content, glucose-to-fructose ratio, sorbitol content, and serving size may contribute to these variations.

HFI Versus Fructose Malabsorption

HFI should not be confused with fructose malabsorption.

Hereditary Fructose Intolerance

HFI is:

  • A genetic metabolic disease
  • Caused by ALDOB mutations
  • Potentially life-threatening
  • Associated with hypoglycemia and organ damage

Fructose Malabsorption

Fructose malabsorption is:

  • A digestive absorption disorder
  • Relatively common
  • Usually not dangerous

Symptoms typically include:

  • Bloating
  • Gas
  • Diarrhea
  • Abdominal discomfort

Unlike HFI, fructose malabsorption does not involve toxic accumulation of fructose metabolites.

Diagnosis

Because HFI can be serious, accurate diagnosis is important.

Genetic Testing

The preferred diagnostic method is ALDOB genetic testing, which may include:

  • Targeted mutation panels
  • Sequencing of the ALDOB gene
  • Expanded metabolic disorder panels
  • Whole exome or genome sequencing

Clinical Evaluation

Physicians may also assess:

  • Dietary history
  • Reactions to fructose-containing foods
  • Blood glucose levels
  • Liver function
  • Kidney function

Why Breath Testing Is Not Recommended

The hydrogen breath test used for fructose malabsorption is not recommended for diagnosing HFI.

Because the test requires fructose ingestion, it may trigger severe metabolic reactions in individuals with HFI. Genetic testing is considered the safer and more reliable diagnostic approach.

Management and Treatment

The primary treatment for HFI is lifelong avoidance of:

  • Fructose
  • Sucrose
  • Sorbitol

Individuals often need to avoid:

  • Fruit juices
  • Apples
  • Pears
  • Honey
  • High fructose corn syrup
  • Sweetened beverages
  • Sugar-free products containing sorbitol

When diagnosed early and managed carefully, individuals with HFI generally have an excellent prognosis and normal life expectancy.

Factor V Leiden: A Separate Genetic Condition

Factor V Leiden is a distinct inherited condition unrelated to HFI. While HFI is caused by mutations in the ALDOB gene, Factor V Leiden results from a mutation in the F5 gene, which plays a role in blood clotting.

According to the College of American Pathologists (CAP) Consensus Conference Statement, testing for Factor V Leiden may be appropriate in certain patients with a personal or family history suggestive of abnormal blood clotting disorders.

What Is Factor V Leiden?

Factor V Leiden causes clotting factor V to become resistant to normal inactivation, creating a tendency toward excessive blood clot formation.

Potential complications include:

  • Deep vein thrombosis (DVT)
  • Pulmonary embolism
  • Clotting after surgery
  • Pregnancy-related clotting complications

Inheritance

Factor V Leiden may occur as:

  • Heterozygous (one altered copy)
  • Homozygous (two altered copies)

Individuals with two altered copies generally have a higher risk of clotting complications.

Relationship to HFI

There is currently no established biological connection between HFI and Factor V Leiden. However, a person may inherit both conditions independently.

Although the disorders affect different pathways, factors such as dehydration, illness, hospitalization, or liver dysfunction may influence overall health considerations in individuals who carry both genetic conditions.

Conclusion

Hereditary Fructose Intolerance is a rare but serious genetic metabolic disorder caused by mutations in the ALDOB gene. Deficiency of the aldolase B enzyme prevents normal fructose metabolism, leading to toxic accumulation of fructose-1-phosphate and potentially severe symptoms, including hypoglycemia, vomiting, liver dysfunction, and growth problems.

Genetic markers such as i5012665 (rs387906225, Delta4E4) may provide clues about carrier status or disease risk, but consumer DNA testing alone cannot establish a diagnosis. Clinical evaluation and confirmatory genetic testing remain the gold standard for diagnosis.

Factor V Leiden is a separate inherited condition involving the F5 gene and increased blood clotting risk. While it has no direct biological relationship to HFI, both conditions can be identified through genetic testing and may coexist in the same individual.

Early recognition, appropriate genetic testing, and careful dietary management allow most people with HFI to lead healthy lives and avoid serious complications.

References:

Hereditary fructose intolerance https://medlineplus.gov/genetics/condition/hereditary-fructose-intolerance/

Fructose-1-Phosphate Aldolase Deficiency
https://www.ncbi.nlm.nih.gov/books/NBK557761/

Hereditary fructose intolerance: A comprehensive review
https://pmc.ncbi.nlm.nih.gov/articles/PMC9331401/

American College of Medical Genetics Consensus Statement on Factor V Leiden Mutation Testing https://pmc.ncbi.nlm.nih.gov/articles/PMC3111091/

A Novel Frameshift Mutation of the ALDOB Gene in a Korean Girl Presenting with Recurrent Hepatitis Diagnosed as Hereditary Fructose Intolerance 
https://pmc.ncbi.nlm.nih.gov/articles/PMC3286731/

 

© 2000-2030 Sieglinde W. Alexander. All writings by Sieglinde W. Alexander have a five-year copyright. Library of Congress Card Number: LCN 00-192742 ISBN: 0-9703195-0-9

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